01 Interface&Signalingnew

Interface and Signaling SSMC Training Center

Network optimization SSMC Training Center© 2003 SSMC TI

1

Interface and Signaling

Contents 1 Air Interface - Um 2 1.1 Layer 1 - Um 5 1.2 Layer 2 - Um 45 1.3 Layer 3 - Um 53 2 Interface Abis 71 3 A-Interface/Signaling System CCS7 104 4 Signaling Sequences 148 4.1 Complete Call Sequences 149 4.2 Message Flow of Basic Circuit Switched BSS Procedures 153 5 TEMS Investigation 176 6 K1205 Protocol Tester 196

SSMC Training Center Air Interface - Um

1 Air Interface - Um

SSMC Training Center Network optimization© 2003 SSMC TI

2

Air Interface - Um SSMC Training Center

The MS is linked to the fixed PLMN structure via a radio link. The air or radio interface Um describes the radio link function. The MS/BSS interface must ensure:

use of the same standard interface by the MS and terminal equipment (TE) use of MSs from different manufacturers in the whole system area of the GSM network connection with terminal equipment using the same identifiers and codes independent of the respective location of the unit

The transmission of speech, data and signaling is carried out on the air interface Um via radio channels (RFCs). The RFCs form layer 1 of the GSM system air interface. Layer 1 (Um) is described in GSM-Rec. 04.04.


3


Layer 3

CC SS SMS

CM MM RR

Layer 2

Layer 1

Logik

Physik

Fig. 1 Layer 1 - 3 of the air interface Um

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1.1 Layer 1 - Um Speech and data transmission on the air interface Um is carried out via the physical channels. A physical channel is defined by a specific carrier pair (RFC = Radio Frequency Channel) in the UL and DL and the number of the time slot in the TDMA frame. Layer 1 (physical Layer: GSM 04.04) is a physical bi-directional point-to-point connection in multiframe mode. Layer 1 communicates with layer 3 directly according to channel management and measurement control. The physical layer will offer layer 2 appropriate channels by usage of the following functions: Burst transmission Error correction and -detection Supervision of RSS Link Control

Furthermore the layer 1 protocol defines the mobile station's search for a suitable BCCH and the seizure of DCCH through the MS (after allocation by the base station)


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RFC174

RFC1

RFC2

7

6

5

4

3

2

1

RFC3

0

TDMA

UL

FDMA

7

6

5

4

3

2

1

RFC3

0

7

6

5

4

3

2

1

RFC2

0

RFC1

RFC174

TDMA

FDMA

DL

Fig. 2 Physical channel in the FDMA and TDMA frame

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1.1.1 The TDMA Frame

A TDMA frame is divided into 8 time slots (= TS). The whole TDMA frame lasts 4.615 ms, an individual time slot 0.577 ms.

A physical channel is assigned exactly one time slot TS in the TDMA frame. Each subscriber receives a time slot and sends all 8 time slots1 once. Transmission is not allowed outside the allocated time slots TS (i.e. after the TS has expired) so other physical channels are not exposed to interference.

1With full rate transmission; with half rate transmission every 16 time slots; HSCSD and GPRS are not yet taken into consideration


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TDMA-frame

4,615 ms

0 1 2 3 4 5 6 7

0,577 ms

0 1 26 7

Fig. 3 Assignment / repeat of a TDMA frame

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1.1.2 Burst / Burst Types Sending the information in the individual time slot of 0.577 ms with a permanently defined bit sequence is called a burst. The burst is realized by the MS by switching on, transmitting briefly and switching off the transmitter again.


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Time structure of the time frame / bit sequence A time slot is defined at a time frame of 577µs (to be precise: 576 12/13 µs ≅ 576.923 µs). This time frame is divided into 156.25 bit. This means an individual bit has duration of 3.6923 µs. The 156.25 bits are used as follows: 142 bits for information transmission, 3 bits each as tail bits (TB) for edge limitation of the time slots. They are also

used as protection zones if a neighboring channel happens to interfere with the first or lasts bits. 8.25 bits as a guard period (GP) (exception: the GP for access burst is 68.25 bits

long) for collecting variable run or reception times (determined by the distance BTSE ↔ MS).


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Burst

. . . 7 0 1 2 3 4 5 6 7 0 1 . . .

TB3 142 ? Information�

Burst

. . . 7 0 1 2 3 4 5 6 7 0 1 . . .

TB3 142 ? Information� TB

3GP8,25



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Fig. 4 Breaking down a time slot into bits


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Realization of information transmission in the burst As a rule 142 bits of information transmission are realized in a burst presented as "1" or "0" as indicated below. They are in the time middle of the burst transmission in the "useful part". The two 3 tail bits (TB) on the edge of the information section provided as security zones are realized as constant transmission of "0". No information is transmitted in the guard period (GP). There are 5 different types of burst Normal burst Frequency correction burst Synchronization burst Access burst Dummy burst

Each of these bursts has a different configuration and has a particular purpose.

The normal burst It contains 2 x 3 bits as tail bits (TB); 2 x 57 encrypted data bits which carry the actual information 2 x 1 bit as a "stealing flag" which tell the receiver that data transmission is being

interrupted briefly and signaling data is being transmitted instead of useful data (or vice versa). 26 bits for synchronizing and problem detection (training sequence), which allow

both the BS and the MS to synchronize themselves to a burst and allocate the data bits exactly. Distorted or incomplete received signals can thus be reconstructed. 8.25 bits guard period (GP) for collecting run times and reception times

(determined by the distance BTSE ↔ MS).


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TB Information S Training Sequence S Information TB GP

148 bit = 546,12 µs (+8,25 bit = 30,44 µs )

3 57 1 26 1 57 3 8,25 bit

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Fig. 5 Normal burst

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13


Frequency correction burst The frequency correction burst is transmitted from the BTS for frequency synchronization. The bit sequence of the fixed bits corresponds with an unmodulated carrier, i.e. a pure sine wave, so the MS can synchronize itself to the preset frequency. The repeat of frequency correction bursts is also known as the frequency correction channel (FCCH). The frequency correction burst consists of: 2 x 3 bit tail bits (TB); 142 bit as fixed bits (sine wave2) for frequency synchronization; 8.25 bit guard period (GP);

2To be more precise: the fixed bits (142 x signal „0“) lead via this modulation, to a sinusoidal signal for this period with a frequency being 67,7 kHz above the carrier central frequency


14


TB fixed Bits TB GP

3 142 3 8,25 bits

Fig. 6 Frequency correction burst

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15


Synchronization burst The MS receives the first information on the BS from the synchronization burst allowing it to synchronize time on the base station. The burst contains a long training sequence, the TDMA number and the identity code of the BS, BSIC3. The TDMA frame number is required as one of the parameters for encryption. The synchronization burst is transmitted together with the frequency correction burst in the TDMA time slot zero. The repeat of synchronization bursts is called synchronization channel. The synchronization burst consists of: 2 x 3 bit tail bits (TB); 2 x 39 bit which contain the TDMA frame number and the identity code of the BS

(BSIC); 64 bit training sequence for time synchronization and fault detection; 8.25 bit guard period (GP);

3BSIC ( Base transceiver Station Identity Code): Identity code of the BTS allowing the MS to distinguish between different BTS; it consists of 6 characters: 3 characters for the NCC (Network Color Code = PLMN identity) and 3 characters for the BCC (Base Color Code) which allows different RFCs with the same frequency in neighboring clusters to be distinguished.


16


TB Information Training Sequence Information TB GP

3 39 64 39 3 8,25 bits

Fig. 6 Synchronization burst

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17


Access burst The access burst is used for the MS contact setup with the BTSE. It is characterized by a long protection time (GP = 68.25 bits or 252 µs), which takes the signal run time4 from MS to BTSE into consideration. The MS does not know the distance to the BTSE first of all and therefore does not know how the transmission has to be staggered (moved forward). The access burst consists of: 8 + 3 bit tail bits (TB); 41 bit synchronization sequence; 36 bit information bits; 68.25 bit guard period (GP);

Dummy burst The dummy burst is sometimes sent as padding if there is no other information. It does not contain any information but has the same format as the normal burst.

4Note: The length of the access burst is decisive for the maximum cell size of a GSM900 cell. When a contact is setup with an MS, the 68.25 bits with a duration of 252 µs are sufficient as a security distance for 3 x 108 m/s x 252 µs = 75.6 km. The cell radius must therefore be less than 37.8 km taking the way BTSE → MS → BTSE into consideration


18


TB Synchro.- Sequence Information TB GP

8 41 36 3 68,25 bits

Fig. 8 Access burst


19


GMSK - Gaussian Minimum Shift Keying The information to be transmitted consisting of a sequence of binary data (bit sequence) must be modulated on an information carrier with a specific rate (bit rate). The receiver must then be able to remove them from this carrier. To obtain the best possible bandwidth utilization taking the minimum requirements for transmission quality into consideration, a frequency modulation method was chosen for the GSM system. It is known as GMSK (Gaussian Minimum Shift Keying). In principle the bandwidth of a radio channel (RFC) of 200 kHz varies here around the center of the bandwidth (carrier frequency ft) with a maximum frequency displacement ∆f = ± 67.7 kHz5 .

MSK - Minimum Shift Keying MSK is a frequency shifting modulation process, which involves the information in the instantaneous frequency of the HF signal. This process stands out because of the continuous phase6 processing of the modulation signal resulting in excellent bandwidth utilization. The binary signal is modulated7 on the carrier using a modulation index η = ∆f/fmod = 0.5. The instantaneous frequency of the HF signal changes with the applied modulation data. When there is a "1", the carrier frequency ft is increased by ∆f, when there is a "0" decreased by ∆f. With a modulation index of 0.5 ∆f corresponds with the half modulation frequency fmod.

With MSK the phase angle ϕ of the carrier is changed linearly and continually during the bit duration T. It is changed by +90° for a logical "1" at the modulator input and by -90° for a "0". The frequency of the HF signal can be seen in the context of the phase relationship. It is also obtained from the trajectory of the phase path or the phase path is obtained from the integral of the frequency path.

∆f can also be calculated from bit duration T and the change in the phase relationship (∆ϕ).

∆f = (∆ϕ/∆t) / 2π;

with ∆ϕ = π/2 (90°) and ∆t = T = 3.6923 µs hence:

∆f = 1/(4T) = 1/(4*3.6923µs) = 67.7 kHz

5 ∆f = 1/(4T) applies; T = duration of a bit = 3.6923 µs 6 i.e. there is no phase jittering 7 ∆f = carrier deviation; fmod = modulation frequency; fmod < 1/2 bit rate fbit


20


MSK ModulationPhase response

Binary

signal

Frequency

response

Phase

+180�

+90�

t

-90�

-180�

1

0

f f

f

f

f

Fig. 9 Frequency and phase response with the MSK modulation process

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21


GMSK Reducing the bandwidth required for MSK can be achieved by prefiltering the data signal. The "increments" of the data (0 ↔ 1) and thus also frequencies or unsteadiness of the phase path result in a comparably wide spectrum. To reduce the bandwidth requirement by means of improved attenuation of the side bands a low-pass prefilter with the pass through characteristic of a Gaussian bell-shaped curve is used. The filter used with bandwidth B8 has the following impulse answer (Rec. 05.04):

H t T e with B T

H f e

t T

B f

( ) / * / *

( )

/

(ln / )*

= =

=

−

−

1 2 2 22 2 2

2 2

2

2 2

Π Πσ σσ Π

The data signals Gaussian filtered here have "softer" transitions thus affecting the phase path. A frequency or phase change without jumps (continuous) results.

1.1.3 Time Organization (Framing) The transmission of the control and user information (speech/data) takes place in physical channels. A time slot is available in the TDMA frame every 4.615 ms. The information is transmitted according to specific time schemas, i.e. certain contents are repeated at specific time intervals. This process, i.e. the periodical repeat of the TDMA frame is called "framing".

80.3 was chosen as a standardized filter bandwith for the Gauss filter, i.e. bandwidth B * bit duration T ≡ 0.3; given B = 81.25 kHz


22


RFC1

RFC2

7

6

5

4

3

2

1

RFC3

0

TDMAFrame

FDMA

Time

t

Frequency

0123456

.

.

.

.

4647484950

0123456

.

.

.

.

2425

BCCH-Multiframe

TCH-Multiframe

RFC174

.

.

.

.

Fig. 10 Physical channels / traffic and control channel multiframe

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23


Multiframe TDMA frames belonging together in a first framing level are called multiframes. There are 26 TDMA frames in a user channel9 multiframe, in a control or signaling channel multiframe there are 51 TDMA frames. The control channel multiframes are transmitted as a rule in time slot 0 of one of the radio channels (RFCs) from a BTSE, the remaining time slots are available for user channel multiframes.

9Note: Not only subscriber information (speech/data) can be transmitted in a „traffic channel“. If the signaling requirement increases, signaling can also be transmitted via a traffic channel. A change between subscriber information and signaling is indicated by the so-called „stealing flags“ in the normal burst.


24


0 1 2 49 50

0 1 2 3 4 5 6 7

8 Time slot = 1 TDMA frame4,615 ms

1 Time slot

BURST = Contents of a time slot

156,25 bit = 576,88 µs(1 bit = 3,692 µs)

0 1 2 24 25

1 Multiframe for Speech/Data 2)26 TDMA frame = 120 ms

1) Signaling channels

2) User channels andassociated signalingchannels

Time organization of the air interface

1 Multiframe for signaling 1)51 TDMA frame = 235,38 ms

Fig. 11Multiframe

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25


The multiframe for user information (full or half rate transmission) will be used at this point as an example of multiframe time organization. The diagram shows the periodical repeat of the fixed structure of certain "logical contents" for a user channel with half and full rate transmission. All 26 TDMA frames repeat specific contents. This is necessary because not only user information (data, speech) is transmitted in the traffic channel connection (called TCH here) but also further specific signaling information (SACCH) has to be transmitted repeatedly at fixed intervals in a traffic channel multiframe. The information (user information signaling) is transmitted between MS and BTS as burst in “physical channels“. To differentiate the contents a division into "logical" channels is useful. These "logical channels" specify therefore certain contents of the transmission over the air interface. In particularly for signaling different contents and therefore "logical channels" are relevant. They are repeated in the signaling channel multiframe every 51 TDMA frames.


26


26 TDMA frame 120 ms

A full rate TCH

T/t TDMA frame for TCHA/a = TDMA frame for SACCH/T

Two full rate TCH

UPLINK / DOWNLINK: Traffic Channel (TCH)

T T T T T T T T T T T T A T T T T T T T T T T T T -

T t T t T A T t T at T tt T t T t T t t T t T t T

Fig. 12 Multiframe for a user channel

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Superframe / Hyperframe The data packets from the time slots are compiled in even higher frame structures in addition to this first framing level of the merging of the TDMA frames to multiframes. These are called superframes and hyperframes. A superframe comprises 26 x 51 = 1326 frames and is thus 6.12 s long. The superframe is the smallest common multiple of traffic channel multiframes (26 frames) and control or signaling channel multiframes (51 frames). The time window of a superframe is the shortest cycle in which the organization of all channels is repeated. Some characteristics of the channel organization are excluded from this repeat. These are contained in the hyperframe. The hyperframe is the numbering period. It comprises 2048 superframes and is thus exactly 12,533.760 s or 3 h 28 min 56.76 s long. It is a multiple of all cycles described up to now and determines all transmission cycles or periods on the air interface in practice.


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Hyperframe = 2048 Superframe

Superframe = 26 x 51 (Multi-) Frames

TCH Multiframe

TDMA Frame

BCH Multiframe

0 1 3 24 25 0 1 2 3 4 49 50

0 1 2 3 4 5 6 7

2

Fig. 13 Time organization: multiframe, superframe and hyperframe

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1.1.4 Adaptive Frame Alignment

Adaptive frame alignment is the time condition between uplink (UL) and downlink (DL). The TDMA frames (UL) running from the mobile station (MS) to the base station (BS) or especially the transmission and reception station (BTSE) are delayed by 3 time slots (burst periods) compared with the (DL) TDMA frame running in the opposite direction. The BTSE sets the frame (master), the MS has to adapt itself to the presetting. The delay of 3 time slots (= 1.73 ms) is GSM-defined. This GSM convention is set up in such a way that the numbering of the time slots can be identical both in the UL and the DL direction. The time delay allows the mobile station to avoid sending and receiving at the same time. This means substantially simpler technical implementation as the MS receiver does not have to be protected against the transmitter from the same MS ("signal isolation"). The so-called "combining" of antennas is thus not necessary.

Timing advance

There is a problem, however, when implementing this convention. If the distance between the BTSE and the MS is greater, the delay due to the run time of the signals must be taken into consideration. Even at the speed of light (3 x 108 m/s) the radio signals also require a specific time to bridge the path between the BTSE and the MS. With a maximum cell radius (GSM900) of approx. 35 km this means a delay of approx. 0.1 ms for the path BTSE - MS or of approx. 0.2 ms for a "round path". This delay in the run time must be taken into consideration when the signal is sent from the MS because it is absolutely necessary that the BTSE receives the signals (bursts) from the different MS in the correct time range. Bursts can otherwise overlap time slots from neighboring time slots and thus reduce the transmission quality substantially or even lead to a communication breakdown. This problem can be solved by the MS transmitting its signals earlier and compensating the run time delay. This compensation or its amount is called the "timing advance" (TA). The exact relocation between DL and UL from the viewpoint of the MS is 3 time slots minus the timing advance, i.e.: 1.73 ms - TA. The duration of the timing advance is measured by the BTSE and transferred to the MS. This takes it into consideration within the framework of adaptive frame alignment and signals the total relocation (1.73 ms - TA) to the MS so the MS can take it into consideration when sending its bursts.


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Mobilestation(MS)

Information for MS on the �Timing Advance“

Transmitter

Receiver

∆t = 3 Time slots

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

2 x Run time (TA)

BS transmission/receive station (BTS)

Fig. 14 Adaptive frame alignment

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1.1.5 Frequency Hopping

Frequency hopping means that RFC physical channels10, therefore the transmit channel and consequently the transmit frequency are changed to a set algorithm. The time slot is not changed. The logic behind frequency hopping is to guarantee that all channels have the same high degree of transmission quality by dividing possible interference occurring in only one RFC over all available channels. Frequency hopping is used to reduce or evenly distribute signal losses. These can be caused by screening of an MS in a vehicle or due to multipath propagation (direct signal + on trees, houses, mountains,... reflected signals) as a result of negative interference. As the local occurrence of these signal losses is directly dependent on the wave length of the radio signal (approx. 33 cm at 900 MHz), changing the transmission frequency will also lead to a change in the radio wave propagation. This allows great transmission losses to be minimized. As well as reducing interference, frequency hopping also improves protection against eavesdropping. The BTSE controls optional frequency hopping. As the MS also has to carry out these the BTSE also transmits the frequency hopping algorithm via a BCCH. This BCCH is therefore not affected by the frequency hopping.

10The exception is the channels of the RFCs on which the BCCH is sent


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Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5TCH

RFC 1

RFC 2

RFC 3

RFC 4

RFC 5

TDMA Frame

Fig. 15 An example of frequency hopping

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1.1.6 Logical Channel Types

A multitude (for signaling in particular) of different "logical channels" or "logical channel types" is used in the GSM system for transmission via the air interface. These logical types: traffic channels signaling channels


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CHANNELS

UL+

DL

UL+

DL

DL DL UL

UL + DL

TRAFFICCHANNELS

SIGNALINGCHANNELS

BROADCASTCONTROL

CHANNLES

DEDICATEDCONTROL

CHANNLESFULLRATE

HALFRATE

COMMONCONTROL

CHANNLES

TCH/F TCH/H BCCH FCCH SCH PCH NCH AGCH RACH SACCH SDCCH FACCH

Fig. 16 Hierarchy of the logical channels

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1.1.6.1 Traffic Channels

Traffic channels TCH The task of the traffic channels is to transmit coded speech and data information from the mobile subscriber. Two general forms of a traffic channels are defined: a) Full rate traffic channels (TCH / F)

This channel transmits speech on the air interface Um at a transmission rate of 13 kbit/s (TCH / FS) or data at 9.6 kbit/s (TCH / F9.6), 4.8 kbit/s (TCH / F4.8) or ≤ 2.4 kbit/s (TCH / F2.4).

b) Half rate traffic channels (TCH / H) Speech is transmitted at 6.5 kbit/s (TCH / HS), data is transmitted at 4.8 kbit/s (TCH / H4.8) or ≤ 2.4 kbit/s (TCH / H2.4).

1.1.6.2 Signaling Channels The signaling channels are organized into 3 types according to their tasks: Broadcast control channels: BCCH Common control channels: CCCH Dedicated control channels: DCCH


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Broadcast control channels BCCH The broadcast control channels BCCH are used for synchronizing and transmitting the cell-specific data from the BTSE to the MS. They only work in downlink (DL) direction, i.e. from the BS in the direction of the MS. There are the following according to tasks: Frequency correction channel FCCH:

allows exact frequency matching for MS Synchronization channel SCH:

after frequency synchronization (by the FCCH) the MS receives further information via the SCH in order to continue with the check-in procedure. The information contains the BSIC and the current TDMA frame number Broadcast control channel BCCH:

contains further information which the MS requires as a reference to the cell (e.g.: channel combination, frequency hopping sequence, cell identification CGI)

Common control channels CCCH The common control channels CCCH are used to control access to the BTSE or the MS. They are unidirectional channels, i.e. they work in either downlink (DL) or uplink (UL) direction There are the following according to tasks: Paging channel PCH:

used (DL) by the BTSE to call the MS Notification Channel NCH:

used (only DL) to notify mobile stations of voice group and voice broadcast calls. Random access channel RACH:

used by the MS to request a signaling channel (UL) from the network or to react to a PCH. Access grant channel AGCH:

assignment of a signaling channel by the BTSE (network) for the MS (DL).


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. . . . . . . . . . . . . . . Dedicated control channels DCCH Dedicated control channels DCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The group of dedicated control channels DCCH also comprises 3 channels: The group of dedicated control channels DCCH also comprises 3 channels:

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stand alone dedicated control channel SDCCH: Stand alone dedicated control channel SDCCH:

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Bi-directional and used for call setup. Authentication and other main signaling functions takes place here. The MS is assigned a specific TCH with the help of the SDCCH.

Bi-directional and used for call setup. Authentication and other main signaling functions takes place here. The MS is assigned a specific TCH with the help of the SDCCH.

. . . . . . . . . . . . . . . . . . . Slow associated control channel SACCH: Slow associated control channel SACCH:

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always coupled to an SDCCH or with a TCH. Signaling information (control and measuring parameters) is exchanged between the MS and BTSE via the SACCH.

always coupled to an SDCCH or with a TCH. Signaling information (control and measuring parameters) is exchanged between the MS and BTSE via the SACCH.

. . BS: BS: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

transmits network-specific information using SACCH to keep the MS up to date on any changes in the cell parameters. Furthermore the control commands for timing advance and power control are transmitted by the BS to the MS via the SACCH.

transmits network-specific information using SACCH to keep the MS up to date on any changes in the cell parameters. Furthermore the control commands for timing advance and power control are transmitted by the BS to the MS via the SACCH.

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. . MS: MS: . . . . . . . . . . . . . . . . . . . . . . . . .

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transmits measuring results (e.g. receive level) to the BS to support them in decisions on the handover. It also informs the BS of the current values of transmission power and timing advance. This function is known as a measurement report.

transmits measuring results (e.g. receive level) to the BS to support them in decisions on the handover. It also informs the BS of the current values of transmission power and timing advance. This function is known as a measurement report.

. . . . . . . . . . . . . . . . . . . Fast associated control channel) FACCH: Fast associated control channel) FACCH:

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activated when the signaling requirement increases in certain situations (e.g. during a handover). The FACCH is transmitted instead of a TCH. The "stealing bits" in the TCH indicate the channel change.

activated when the signaling requirement increases in certain situations (e.g. during a handover). The FACCH is transmitted instead of a TCH. The "stealing bits" in the TCH indicate the channel change.

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38


1.1.7 Multiframe, Channel Combination The description of the multiframe mentioned that there was only one possibility of arranging the logical channels in multiframes. Moreover there are 7 different combinations (channel combinations) for arranging logical channels in multiframes. In the channel combinations11 listed below RACH, PCH and AGCH are combined in CCCHs as they all involve the allocation of a channel to a subscriber: I) TCH/F + FACCH/F + SACCH/F II) TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1) III) TCH/H(0) + FACCH/H(0) + SACCH/H(0) +

TCH/H(1) + FACCH/H(1) + SACCH/H(1) IV) FCCH + SCH + CCCH + BCCH V) FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4 VI) CCCH + BCCH VII) SDCCH/8 + SACCH/8

F0

S1

BCCH2 - 5

CCCH6 - 9

F10

S11

CCCH12 - 19

F20

S21

CCCH22 - 29

F30

S31

CCCH32 - 39

F40

S41

CCCH42 - 49

I50

DL: F = FCCH, S = SCH, B = BCCH, C = CCCH, (PCH, AGCH), I = idle

UL: R = RACH

R0

R1

R10

R11

R20

R21

R30

R31

R40

R41

R50

Fig. 17 Multiframe for channel combination IV) FCCH + SCH + CCCH + BCCH

11/4 or /8 means up to 4 / 8 dedicated and associated connections to MS


39


F S B C F S C C F S D0 D1 F S D2 D3 F S A0 A1 I

51 TDMA Rahmen = 235,38 ms

DOWNLINK: Broadcast Control Channel (BCCH), Common Control Channel (CCCH)+4 Stand Alone Dedicated Control Channels (SDCCH/4)

UPLINK: Common Control Channel (CCCH)+4 Stand Alone Dedicated Control Channels (SDCCH/4)

D3 R R A2 A3 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

D3 R R A0 A1 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

F S B C F S C C F S D0 D1 F S D2 D3 F S A2 A3 I

A TMDA frame for SACCH B BCCH C CCCH D SDCCH F frequency correction burst R RACH S synchronized burst I idle Fig. 18 Multiframe for channel combination V)

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40


Purpose / use of the different channel combinations: I) - III) Call and data transmission in a 26 TCH frame; I) Combination I) is primarily used to transmit TCH/F (full rate speech). In

combination I) the first 12 frames (0 - 11) are used for call or data transmission, a SACCH is then transmitted (frame 12) and also 12 frames (13 - 24) for call and data transmission. The last frame (25) is not used (I: idle).

II) III) Combination II) and III) are primarily used for transmitting user data at half rate. 2 TCH/H have to "share" the 26 multiframe with their associated control channels. Data from the first or second subscriber is alternately filled into the frame. The SACCH of the 1st subscriber is in frame 12, the SACCH of the 2nd subscriber in frame 25. This means there are no empty (idle) frames.

The FACCH does not have a fixed frame in combination I) to III). If signaling is necessary, indicated by the "stealing flag" in the normal burst, a 20 ms long part of the multiframe which is 120 ms long in total is occupied with FACCHs instead of TCHs. V) – VII) BTSE ↔ MS signaling: V) Channel combination V) is the minimum configuration for a base

station. It is mostly used when a BTS is only equipped with 1 or 2 RFCs. Channel combination V) may only be used once in a cell because the mobile station searches for the frequency correction channel FCCH for synchronizing and the channel for time synchronization SCH. It is transmitted to time slot 0 of an RFCs („base frequency12“). Channel combination V) and IV) rule each other out.

12The base frequency can be any RFC, it must be sent constantly however


41


IV) Channel combination IV) is mainly used for BTS with several RFCs as it provides the common control channels CCCH with a lot of space. It may only be used once for the same reasons as with combination V) (in time slot 0 of one of the RFC). As opposed to combination V) there are no dedicated channels in combination IV). Channel combination VII) is thus also required when channel combination IV) is used.

VI) A BTS can contain up to 16 RFCs in the GSM system. When a lot of RFCs are used (corresponding with a very high traffic volume in the cell) further task sharing can be useful in the channel combination. Channel combination VI) which only contains common control channels CCCH as well as the BCCH is used for this. This means that it is necessary to also use combination IV) and VII) in addition to channel combination VI). Combination IV) is in time slot 0 of the base frequency and VI) going onto 2, 4 and 6.

VII) Channel combination VII) is used to accommodate the dedicated channels SDCCH and SACCH each for up to 8 connections between BTSE and MS and is used as a supplement to combination IV) and VI).

Remark: Meanwhile there are channel combinations existing, which inhabit the

Cell Broadcast (for SMS CBS).


42



43


1.2 Layer 2 - Um-Interface


44


The task of layer 2, the data circuit layer, is so-called "linking", i.e. the safe transmission of signaling messages via an individual signaling link. Layer 2 (linking) protocols in the different GSM interfaces are the same to a great extent, they have very similar functions. The main tasks of layer 2 are generally the structuring of the information to be transmitted on the communication channel: Fault detection and correction Stable transmission, i.e. guaranteed free of errors; otherwise transmission repeat Disassembly of the individual data stream and reconstruction Flow control

Layer 2 (Data Link Layer) defines the structure of the 23-byte blocks in the CCM and in particular the numbering and acknowledgment of the blocks.


45


CC

CallControl

SSS

SupplementaryServicesSupport

SMS

ShortMessageService

CM Connection Management

MM Mobility Management

RR Radio Resource Management

Layer 2 Data Link Layer

Layer 1 Physical Layer

Layer 3 Network Layer

Fig. 19 Layers 1 to 3 at the air interface


46


The structure of a 23-byte transmission block in the SDCCH, FACCH, PCH, AGCH or BCCH is shown in the adjacent figure. (The block structure in SACCH deviates slightly from the illustration, whilst a block in the RACH consists of only one byte). A block of this type (known also as layer 2 frame) begins with an address field (1 byte), a control field (1 byte) and a length indicator (1 byte). The subsequent information field contains the layer 3 data. If the 20 bytes available for this data are not completely used, the residual bytes are filled with the fill bit pattern "00101011" ("11111111" also permissible in uplink direction) in order to attain a total length of 23 bytes. Address field contents: Link Protocol Discriminator (LPD) for discriminating between the GSM protocol

and other protocols (national or manufacturer-specific) Service Access Point Identifier (SAPI) for discriminating between short message

service (SMS) and other layer 3 parts (RR, MM, CC or SSS) in the information field. (A special layer 3 format is used for SMS, and the SMS messages are numbered independently of the other messages in the control field). Command/Response Field bit (C/R) for discriminating between commands

(messages transmitted on own initiative) and responses (reactions to received commands).

The control field is used to number and acknowledge the frames. Its structure is shown in the next figure. The length indicator specifies the length in bytes of the information field. The indicator additionally contains the More Data bit (M) specifying whether the layer 3 message extends to the follow-on layer 2 frame. It may be the case that a layer 3 message is longer than 20 bytes and must therefore be distributed over several layer 2 frames. In this case, the last frame is transmitted with M = 0 and all preceding frames with M = 1 ("Continuation in the next issue"). If the layer 3 messages fits into one layer 2 frame, the More-Data bit of the latter is set to 0 ("End").


47


LPD SAPI C/R

see next figure

1

2

Length M

Address Field

Control Field

Length Indicator

Layer 3

Fill bits

3

n

23

Fig. 20 Structure of a Layer 2 frame (acc. to GSM 04.06)


48


The control field differentiates the following three frame types: Information Frames (I-frames), Supervisory Frames (S-frames) and Unnumbered Frames (U-frames). Information frames are identified by the digit 0 in the least significant bit in the control field. These frames are used for error-protected message transmission. "Error protection" means in this context that the messages are individually numbered and acknowledged, thus allowing the receiver the opportunity to request a repeat transmission in the event of a transmission error or reception fault. Accordingly, the control field in the I-frame contains one send number N(S) and one reception number N(R), each 3 bits in length. The send number numbers consecutively all I-frames running in the same direction on one CCH, whereby short message service (SMS) messages and other layer 3 part messages are counted separately. The reception number specifies which I-frame is next expected in the counterdirection; thus, the number is that of the last correctly-received I-frame + 1. I-frames are always commands and always include an information field. Supervisory frames are identified by the bit combination "01" in the two least significant bits in the control field. These frames are used for acknowledgment of received information frames without simultaneously supplying new information. Therefore, the S-frame control fields have only a reception number N(R) indicating the next anticipated I-frame in the counterdirection. Three types of S-frame are distinguished: Receive Ready (RR): positive acknowledgment in normal operation Receive Not Ready (RNR): positive acknowledgment simultaneously declaring

that due to overload no further I-frames can currently be accepted Reject (REJ): negative acknowledgment (i.e. repeat request)

Supervisory frames can occur as commands or responses; they never include an information field. If information and supervisory frames are exchanged between MS and BSS in a CCH, a layer 2 connection is said to exist in this CCH. The set up of such a layer 2 connection means that both sides allocate storage space for the valid send and reception numbers as well as for the buffering of as yet unacknowledged I-frames (which must possibly be retransmitted). This storage space is released when the layer 2 connection is cleared down.


49


both

both

Command

Response

Command

Command

Response

Frame Format bit pattern CommandResponse

Inform.Field

I Command yes

no

no

no

possible

no

yes

no

possible

S

U

RR

RNR

REJ

SABM

DM

UI

DISC

UA

N(R) P/F 0 0 0 1

N(R) P/F 0 1 0 1

N(R) P/F 1 0 0 1

0 0 1 P 1 1 1 1

0 0 0 F 1 1 1 1

0 0 0 P 0 0 1 1

0 1 0 P 0 0 1 1

0 1 1 F 0 0 1 1

both

N(R) P N(S) 0

Fig. 21Control field structure (acc. to GSM 04.06)


50


As SMS messages are numbered separately from other messages, two independent layer 2 connections can exist in the same CCH: one layer 2 connection for SMS, one for all other layer 3 messages. Layer 2 connections may only be established in SDCCH and FACCH. For this reason, only unnumbered frames are used in all other CCH (i.e. BCCH, AGCH, PCH and SACCH). Unnumbered frames are identified by the digit 1 in the two least significant bits in the control field. These frames contain like their name suggests neither a send number nor reception number. The frames are not acknowledged, therefore, and the receiver cannot request a retransmission. A distinction is made between the following types of unnumbered frames: Set Asynchronous Balanced Mode (SABM): layer 2 connection set up Disconnect (DISC): layer 2 connection clear down Unnumbered acknowledge (UA): positive acknowledgment for SABM Disconnect Mode (DM): negative acknowledgment for SABM; is also used in

cases where an I-frame or S-frame arrives without a layer 2 connection having been established Unnumbered Information (UI): transmission of an information field without layer 2

connection. SABM, DISC and UI are commands; UA and DM are responses. An information field is always included in the UI, but never in the DISC or DM. SABM and UA may optionally contain an information field. As layer 2 connections exist only in the SDCCH and FACCH, UI-frames are used exclusively in the BCCH, AGCH, PCH and SACCH. The P, F or P/F bits shown in table 3 are known as poll bits in commands and final bits in responses. Their standard value is 0. By transmitting a command with P = 1, one side (MS or BSS) can specially request the opposite side to send a response labeled with F = 1. This polling method is used for set up and clear down of the layer 2 connection (SABM or DISC with P = 1, UA with F = 1). The BSS likewise polls the MS to ascertain whether the latter is still accessible. Polling is additionally used when one side reports overload with RNR: the opposite side regularly queries (command RR with P = 1) whether the overload still exists (response RNR with F = 1) or not (response RR with F = 1). For all details of the Layer 2 protocol release refer to GSM Guideline 04.06


51


1.3 Layer 3 - Um


52


1.3.1 Radio Resource -, Mobility - and Connection Management

The layer 3 is composed of three sublayers comprising: the Radio Resource Management (RR) functions the Mobility Management (MM) functions the Connection Management (CM) functions.

The Layer 3 messages can only contain maximal 249 Bytes.


53


Layer 3 Network Layer

CC

CallControl

SSS

SuplementaryServicesSupport

SMS

ShortMessageService

CM Connectioon Management

MM Mobility Management

RR Radio Resuorce Management

Layer 2 Data Link Layer

Layer 1 Physical Layer

Fig. 23 Layer 1 to 3 at the air interface; the sublayers of layer 3


54


1.3.1.1 Radio Resource Management (RR) The Radio Resource management (GSM 04.08) messages will be sent between MS and BTS / BSC. Many RR messages will be transported over the Abis Interface within the RSL / DTAP to the BSC. Radio Resource management procedures include the functions related to the management of the common transmission resources, e.g. the physical channels and the data link connections on control channels. The general purpose of Radio Resource procedures is to establish, maintain and release RR connections that allow a point-to-point dialogue between the network and a Mobile Station. This includes the cell selection/reselection and the handover procedures. Moreover, Radio Resource management procedures include the reception of the uni-directional BCCH and CCCH when no RR connection is established. This permits automatic cell selection/reselection.


55


The elementary procedures for Radio Resource management are as follows: Idle mode procedures:

System information broadcasting Paging RR connection establishment procedures:

Entering the dedicated mode: immediate assignment procedure Entering the group transmit mode: uplink access procedure Paging procedure for RR connection establishment Notification procedure Procedures in dedicated mode and in group transmit mode:

SACCH procedures Channel assignment procedure Handover procedure Frequency redefinition procedure Channel mode modify procedure Ciphering mode setting procedure Additional channel assignment procedure Partial channel release procedure Classmark change procedure Classmark interrogation procedure RR connection release procedure Group receive mode procedures Configuration change procedure

The following table summarizes Radio Resource Management messages:


56


RR Management Messages Remarks Channel establishment messages: ADDITIONAL ASSIGNMENT

IMMEDIATE ASSIGNMENT

IMMEDIATE ASSIGNMENT EXTENDED

IMMEDIATE ASSIGNMENT REJECT

Ciphering messages: CIPHERING MODE COMMAND

CIPHERING MODE COMPLETE

Handover messages: ASSIGNMENT COMMAND

ASSIGNMENT COMPLETE

ASSIGNMENT FAILURE

PDCH ASSIGNMENT COMMAND

HANDOVER ACCESS

HANDOVER COMMAND

HANDOVER COMPLETE

HANDOVER FAILURE

RR-CELL CHANGE ORDER

PHYSICAL INFORMATION

RR INITIALISATION REQUEST

HANDOVER ACCESS

HANDOVER COMMAND

HANDOVER COMPLETE

HANDOVER FAILURE

PHYSICAL INFORMATION

Channel release messages: CHANNEL RELEASE

PARTIAL RELEASE

PARTIAL RELEASE COMPLETE


57


Paging messages: PAGING REQUEST TYPE 1

PAGING REQUEST TYPE 2

PAGING REQUEST TYPE 3

PAGING RESPONSE

System information messages: SYSTEM INFORMATION TYPE 1

SYSTEM INFORMATION TYPE 2

SYSTEM INFORMATION TYPE 2bis

SYSTEM INFORMATION TYPE 2ter




SYSTEM INFORMATION TYPE 5bis

SYSTEM INFORMATION TYPE 5ter








Specific messages for VBS/VGCS: NOTIFICATION/FACCH

NOTIFICATION/NCH

TALKER INDICATION

UPLINK ACCESS

UPLINK BUSY

UPLINK FREE

UPLINK RELEASE


58


VGCS UPLINK GRANT

EXTENDED MEASUREMENT ORDER

EXTENDED MEASUREMENT REPORT

Miscellaneous messages: CHANNEL MODE MODIFY

CHANNEL MODE MODIFY ACKNOWLEDGE

CHANNEL REQUEST

CLASSMARK CHANGE

CLASSMARK ENQUIRY

FREQUENCY REDEFINTION

MEASUREMENT REPORT

SYNCHRONIZATION CHANNEL INFORMATION

RR STATUS

GPRS SUSPENSION REQUEST

Configuration Change messages: CONFIGURATION CHANGE COMMAND

CONFIGURATION CHANGE ACKNOWLEDGE

CONFIGURATION CHANGE REJECT

Application messages: APPLICATION INFORMATION


59


1.3.1.2 Mobility Management (MM)

The Mobility Management (GSM 04.08) messages will be sent between MS and MSC and have no influences to the BSS. The MM messages will be transported over the Abis and A-Interface within the RSL / DTAP and DTAP to the BSC. The main function of the Mobility Management sublayer (GSM 04.08) is to support the mobility of user terminals, such as informing the network of its present location and providing user identity confidentiality. A further function of the MM sublayer is to provide connection management services to the different entities of the upper Connection Management (CM) sublayer. The elementary procedures for Mobility Management are as follows: MM common procedures:

TMSI reallocation procedure Authentication procedure Identification procedure IMSI detach procedure Abort procedure MM information procedure MM specific procedures:

Location updating procedure Periodic updating IMSI attach procedure Generic Location Updating procedure Connection management sublayer service provision:

MM connection establishment MM connection information transfer phase MM connection release

The following table summarizes Mobility Management messages:


60


MM Management messages Remarks Registration messages: IMSI DETACH INDICATION

LOCATION UPDATING ACCEPT

LOCATION UPDATING REJECT

LOCATION UPDATING REQUEST

Security messages: AUTHENTICATION REJECT

AUTHENTICATION REQUEST

AUTHENTICATION RESPONSE

IDENTITY REQUEST

IDENTITY RESPONSE

TMSI REALLOCATION COMMAND

TMSI REALLOCATION COMPLETE

Connection management messages: CM SERVICE ACCEPT

CM SERVICE REJECT

CM SERVICE ABORT

CM SERVICE REQUEST

CM RE-ESTABLISHMENT REQUEST

ABORT

Miscellaneous messages: MM INFORMATION

MM STATUS

MM NULL


61


1.3.1.3 Connection Management (CM)

The Connection Management (CM) sublayer is composed of: Call Control (CC) Short Message Service Support (SMS) Supplementary Services Support (SS)

The CC messages will be sent between the MS and the MSC and will therefore be considered mainly. Every mobile station must support the call control protocol. If a mobile station does not support any bearer capability at all then it shall respond to a SETUP message with a RELEASE COMPLETE message. In the call control protocol, more than one CC entity are defined. Each CC entity is independent from each other and shall communicate with the correspondent peer entity using its own MM connection. Different CC entities use different transaction identifiers. The elementary procedures for circuit switched Call Control are as follows: Call establishment procedures:

Mobile originating call establishment Mobile terminating call establishment Signaling procedures during the "active" state

User notification procedure Call rearrangements User initiated level up- and downgrading Call clearing

Clearing initiated by the mobile station Clearing initiated by the network Clear collision Miscellaneous procedures

In-band tones and announcements Call collisions Status procedures Call re-establishment, mobile station side Call re-establishment, network side DTMF protocol control procedure

The following table summarizes Call Control messages:


62


CC messages Remarks Call establishment messages: ALERTING

CALL CONFIRMED

CALL PROCEEDING

CONNECT

CONNECT ACKNOWLEDGE

EMERGENCY SETUP

PROGRESS

SETUP

Call information phase messages: MODIFY

MODIFY COMPLETE

MODIFY REJECT

USER INFORMATION

Call clearing messages: DISCONNECT

RELEASE

RELEASE COMPLETE

Messages for supplementary service control:

FACILITY

HOLD

HOLD ACKNOWLEDGE

HOLD REJECT

RETRIEVE

RETRIEVE ACKNOWLEDGE

RETRIEVE REJECT


63


Miscellaneous messages: CONGESTION CONTROL

NOTIFY

START DTMF

START DTMF ACKNOWLEDGE

START DTMF REJECT

STATUS

STATUS ENQUIRY

STOP DTMF

STOP DTMF ACKNOWLEDGE


64


1.3.2 Formatting Rules Every layer 3 message is comprised of several parameters, also known as information elements. Section 9 of GSM Guideline 04.08 defines the mandatory and optional parameters for every message. The same parameter may be mandatory for one message and optional for another. Optional parameters bear an identifier (Information Element Identifier, IEI) to designate their presence. The identifier is always located at the beginning of the parameter. Mandatory parameters, by contrast, include sometimes - dependent on the position - an identifier. The parameters are sub-divided into 5 parameter formats (described in GSM 04.07): V (value only) parameters have neither an identifier (IEI) nor a length indicator;

they are mandatory parameters of fixed length. The length is either an integer amount of bytes or 1/2 byte. In the last case, V-parameters of 1/2 byte length are combined to form pairs whenever possible. The first parameter in the combination encompasses the 4 least significant bits, the second parameter the 4 most significant bits. If the total number of V-parameters of 1/2 byte is odd, the 4 most significant bits of the last byte are filled with 0000.

TV (type and value) parameters have an identifier (IEI) but no length indicator. If the length of the contents is an integer amount of bytes, then the IEI is 1 byte in length, and the most significant IEI bit is 0. If the length of the contents is 1/2 byte, then the IEI is likewise 1/2 byte in length. The most significant bit is 1, and the succeeding bits must not be 010 (to distinguish them from T-parameters, see below).

T (type only) parameters have 0 byte content. The communicated information consists solely in the presence or absence of the parameter. Obviously, such parameters can only be considered as optional. The identifier (IEI) is 1 byte in length and begins with 1010 (so that no confusion with TV-parameters is possible). One example of a type-2 parameter is the authorization given in "Location Update Accept" for the Mobile Station to set up a MM connection directly after the location update (i.e. in the same RR connection). This authorization may, or may not, be present.

LV (length and value) parameters have a length indicator but no identifier (IEI); they are mandatory parameters of variable length. The length indicator is the first byte and indicates how many bytes of contents follow.

TLV (type, length and value) parameters have an identifier (IEI) and a length indicator. The IEI is the first byte of the parameter; its most significant bit is 0. The length indicator is the second byte of the parameter and indicates how many bytes of contents follow.


65


Layer 3 parameters (GSM 04.07)

Parameter Format Length integer amount of Bytes Length of 1/2 Bytes

Example: 5 parameters

V alue

T ype,V alue

T ype

L ength,V alue

T ype,L ength,V alue

content

content

0 IEI

content

Length indicator

content

Length indicator0 IEI

0 contentIEI≠ 010

IEI1 0 1 0

content 1content 3content 4content 5

content 2

0 0 0 0

Fig. 24 Parameter formats


66


Each message begins with the same three V-parameters: The protocol discriminator specifies the layer 3 part to which the message belongs. It is a parameter of 1/2 byte length. The transaction identifier (TI) characterizes the transaction ( = CM connection, cf. 2.3). It is a V-parameter of 1/2 byte, too; in conformity with the rules, the protocol discriminator and the TI together fill 1 byte. For RR and MM messages (protocol discriminator = 0110 or 0101), no CM connection is established; for this reason, the TI is replaced by the skip indicator whose value is 0. With a proper TI, the most significant bit serves as TI flag in messages for other TI parts; it is 0 in messages from the side, which set up the transaction, and 1 in messages to the side, which set up the transaction. The three remaining bits from the TI value are freely selected by the initiating side in a transaction set up; the value 111 is not permissible. The message type identifies the nature of the message (e.g. "Handover Command", "Location Update Request", "Setup" and many other examples). It is a V-parameter with a length of 1 byte. The second bit is the send sequence number N(SD). In all messages from the Base Station, as well as in RR messages from the Mobile Station, this bit is 0. In MM and CM messages from the Mobile Station the bit alternately has the values 0 and 1. For the remaining parameters, the protocol may define three different presence requirements: M (mandatory), C (conditional) or O (optional). An M-parameter must always be included in a message of a given type; its absence is reason enough for the receiver to reject the whole message. A C-parameter must be present under certain conditions, but can be absent under other conditions. An O-parameter, finally, is never bound to be present; its absence is never sufficient reason for the receiver to reject the message.


67


TI-flag TI-Value

0 N(SD)

Message Type

Transaction identifieror Skip indicator Protocol discriminator

Protocoldiscriminator

Messagetype

Fig. 25 Layer 3 message header (GSM 04.07)

Value

0110

0101

0011

1011

1001

1111

Layer 3 part

Radio Resource Management (RR)

Mobility Management (MM)

Call Control (CC)

Supplementary Services Support (SSS)

Short Message Service (SMS)

reserved for tests

Fig. 26 Protocol discriminator


68


Some examples of layer 3 messages will now be examined. First we shall consider a Radio Resource Management message the "Handover Command" from Base Station to Mobile Station. Apart from the parameters in the message header, the mandatory parameters are the description of the new cell (Cell Description), the specification of the new speech channel (Description of the First Channel) and the required power of the Mobile Station in the new cell (Power Command). Several conditional and optional parameters exist which depend on the cell synchronization or on whether frequency hopping is employed in the new cell. The length specifications indicate the total parameter lengths, i.e. inclusive of identifier and length indicator, where applicable. Thus, V-parameters have the length 1/2 or an integer value. With TV-parameters, the length is 1 if they have 1/2 byte contents and 1/2 byte identifier; otherwise, the length of the contents is 1 byte less than the indicated length (because the first byte is the IEI). T-parameters always have a length of 1 byte. LV-parameters have a length of the contents, which is 1 byte less than the indicated length (here, the first byte is the length indicator). Finally, with TLV-parameters, the length of the contents is 2 bytes less than the indicated length, since the first byte is the IEI and the second byte is the length indicator. For example, the parameter "Real Time Difference" (TLV) has a total length of 3 bytes. When 1 byte is subtracted for identifier and length indicator respectively, 1 byte remains for the content.


69

SSMC Training Center Interface Abis

2 Interface Abis


70

Interface Abis SSMC Training Center

2.1 Layer 1


71


The Abis interface is physically a 2 Mbit PCM System with 16 kbit/s subchannels. These 16 Kbit/s subchannels can be used for signaling and speech. The 16 kbit/s speech information will be transformed in the TRAU to 64 kbit/s.

2.1.1 Structure of the 2 Mbit/s Frame according to CCITT Recommendation G.704

2-Mbit/s-Pulse frame In the direction of transmission the primary multiplexer PCM30 transforms up to 30 signals with different features into 64-kbit/s-digital signals and then combines them by the time division multiplexing procedure to a 2048-kbit/s (2-Mbit/s)-signal. The individual signals can be either LF-speech signals converted by pulse code modulation, or digital signals (e.g. data). In the receive direction a demultiplexer isolates the individual signals out of the 2 Mbit/s signal. The 64-kbit/s-digital signals are then converted again into analog signals. The 2-Mbit/s pulse frame accord. to CCITT-recommendation G.704 consists of 32 time intervals with 8 bits each (octets). In the intervals 1 to 15 and 17 to 31 speech or digital signals are transmitted. Interval 16 contains the channel-associated signaling information (CAS) combined in one multiframe or, optionally, an additional device-specific data channel. In the interval 0 there is an alternate transmission of a frame alignment signal (FAS) or a service word (SVW). In order to isolate the individual signals out of the pulse frame the FAS is searched for in the received 2-Mbit/s-signal. As soon as the bit pattern is recognized, the demultiplexer part of the central multiplexer synchronizes itself to time interval 0. To additionally ensure the synchronization the CRC4-procedure is applied. The service word is used for the transmission of urgent and non-urgent alarms (bit A and bit Sa4), for loop commands (bits Sa6 and Sa7) (CCITT-Redbook: bits D, N and Y1 to Y3).


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Time slots

Coded telephonesignals 1 to 15 ordigital signals1 to 15

Signalinginformation ordigital signalchannels 31

Coded telephonesignals 16 to 30 ordigital signals16 to 30

125 µs

8 bits

0 1 2 15 16 17 30 31

Framealignmentsignal in frames0, 2, 4 ... 14

YNY1X D Y Y Y

Service wordin frames1, 3, 5 ... 15

D = Service bit for urgent alarmX = Bits reserved for international useY = Bits reserved for national use

X 0 0 1 0 1 11

Fig. 27 2-Mbit/s-Pulse frame


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2.1.2 CRC4-Synchronization for Primary Multiplexer

With the data transmission of synchronous 64 kbit/s digital signals it is possible that the bit patterns of the FAS and the SVW are transmitted (either randomly or on purpose) in the time intervals defined for user signals. If there is a synchronization of the receive side demultiplexer to this bit pattern, an isolation of the individual signals is impossible. Therefore, the CRC4-procedure (Cyclic Redundancy Check by 4 bits) described in CCITT-recommendation G.704 is used in addition, to ensure the synchronization. For this, 16 consecutive 2-Mbit/s frames are combined to a CRC4 multiframe consisting of 2 data blocks and of the multiframe parts I and II. The highest rating bits of the service words in the first twelve 2-Mbit/s frames form the multiframe code word ('001011'). Here, the synchronization is based on two criteria: finding the FAS of the 2-Mbit/s frame and the FAS of a CRC4 multiframe. To continually supervise the synchronization, a data block (e.g. block I) is modified in a data transmitter according to a certain algorithm, whereby a rest of 4 bits (the control bits C1 and C4) is left over. These bits are transmitted as highest rating bits in the 2-Mbit frame alignment words of the following data block (block II). The data receiver processes the incoming data block according to the same algorithm as the transmitter. Again, a rest of 4 bits is left over, which are compared individually to the control bits received in the next data block (block II). In case of a correspondence, block I is considered to be error-free. If 915 or more out of 1000 checked blocks were found to be faulty, a new synchronization is started. A CRC4-error is indicated by two E-bits (CCITT-Redbook: Si-bits) at the transmit side; these two E-bits are transmitted as highest rating bits of the service words in the 2-Mbit/s frames 13 and 15 of the CRC4 multiframe. The BER of the 2-Mbit/s-signal can be derived from the number of faulty blocks. Thus, for example, a number of 512 or more faulty blocks within a measuring interval of 1 s results in a BER > 10-3.


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0 1 2 15 16 17 30 31

telephoneor

data

telephoneor

data

signalinginformation

2-Mbit/s-frame

32 x 8 bits = 256 bits

X 0 0 1 1 0 1 1

X 1 D N/Y Y Y Y Y

alternating

bit position

frame alignment signal FAS

service word SW

time slots

0 C1 0 0 1 1 0 1 1 FAS1 0 1 D N/Y Y Y Y Y SW2 C2 0 0 1 1 0 1 1 FAS3 0 1 D N/Y Y Y Y Y SW4 C3 0 0 1 1 0 1 1 FAS5 1 1 D N/Y Y Y Y Y SW6 C4 0 0 1 1 0 1 1 FAS7 0 1 D N/Y Y Y Y Y SW8 C1 0 0 1 1 0 1 1 FAS9 1 1 D N/Y Y Y Y Y SW10 C2 0 0 1 1 0 1 1 FAS11 1 1 D N/Y Y Y Y Y SW12 C3 0 0 1 1 0 1 1 FAS13 E 1 D N/Y Y Y Y Y SW14 C4 0 0 1 1 0 1 1 FAS15 E 1 D N/Y Y Y Y Y SW

16(2-Mbit/s-frame)

multiframepart I

multiframepart II

CRC4-multiframeMFR

1 2 3 4 5 6 7 8

2-Mbit/s-frame mark, FAS CRC4-multiframe codeword (X)

C1 to C4 (X) CRC4-control bits D service bit for urgent alarm E CRC4-service bits for the

reporting of CRC4-errors N/Y service bit for non-urgent alarm

Fig. 28 CRC4 multiframe


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2.1.3 Alarms

AIS Alarm Indication Signal: The AIS signal is an "all-one-signal" which, if an error occurs, is inserted as replacement signal only in forward direction.

D-Bit: If the counterpart gets no signal, a remote alarm is indicated.

2.1.4 PCM Transmission Systems The transmission systems recommended by the CCITT and described below are the PCM30 system, with 2048 kbit/s (CCITT Recommendation G.732), and the PCM24 system, with 1544 kbit/s (CCITT Recommendations G.733); these combine 30 and 24 telephone channels per transmission direction respectively to form a time-division multiplex signal. PCM30 transmission systems are used throughout Europe and in many non-European countries; PCM24 transmission systems have been installed mainly in the USA, Canada and Japan. PCM30 and PCM24 are also known as "primary transmission systems" or basic systems.


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• Common characteristics PCM30 and PCM24

Sampling frequency 8 kHza

No. of samples per telephonesignal 8.000/sb

Pulse frame periodc ssb

µ125/000.8

11==

No. of bits in a PCM word 8 bitsd

Bit rate of a telephone channel b * d = 8.000/s * 8bits = 64kbit/se

• System-specific characteristics

Encoding/DecodingNo. of segments incharacteristic

f

PCM30 PCM24

A-law13

µ-law15

Number of channel time slotsper pulse frameg 32 24

Number of bits per pulse frame(**= additional bit)h d * g = 8 bits * 32=

256 bitsd * g + 1** = 8 bits *24 + 1** = 193 bits

Period of an 8-bit channel timesloti

aprox. 3.9 µs aprox. 5.2 µs

Bit rate of time divisionmulitplex signalk

b * h = 8.000/s * 256 bits =2.048 kbit/s

b * h = 8.000/s * 193 bits =1.544 kbit/s

2568125 ⋅

=⋅ shdc µ

1938125 ⋅

=⋅ shdc µ

Fig. 29 Characteristics of the PCM30 and PCM24 transmission systems


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2.1.5 Interface Codes

A suitable interface code has a maximum of transitions between the different signal levels, even for the transmission of lengthy sequences of identical logical states; it has no dc-component. The survey shows the development of individual codes.


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clock retrieval possible also for adjacent log. 1 bits.

. . . . . . Disadvantage: . . . . . . . . . . . .

. . . . . . . . . . . .no clock information for zero sequences, dc-component.

. . . . . . . . AMI Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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The state log. 1 is represented alternately as positive or negative signal level.

. . . . . Advantage: . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . clock retrieval possible also for adjacent log. 1 bits, no dc-component.

. . . . . . Disadvantage: . . . . . . . . . . . . . . . . . no clock information for zero sequences . . . . .

HDB3 Code

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Is derived from the AMI code. Here, four consequent zero bits are replaced by a 1001 or 0001 combination. This is done in such a way that the signal receiver detects the mutilation of informational contents and cancels it.

. . . . . Advantage: . . . . . . . . . . . . . . . . . . . . Maximum clock information, no dc-component. . . . . . .

. . . . . . Disadvantage: . .

. . None

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This code is applied for the device interfaces from 2 Mbit/s up to 34 Mbit/s (baseband transmission). The exact coding rules are enumerated in the following.

. . . . CMI Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Due to its easy generation with delay lines and simple gate functions the CMI code is suited especially for interfaces with high bitrates. Therefore, this code is standardized for the 140 Mbit/s device interface.

RZ Code A log. 1 is represented as half-bit with a change of signals levels from Low → High → Low.

Advantage:

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A rather important advantage of the interface code is the possibility it offers to detect transmission errors by supervising the coding rules. With the HDB3 code, for example, the receiving of four zero bits would represent the violation of a coding rule, i.e. at least one bit error must have been occurred during transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The standardization of interface codes only refers to device interfaces. The codes for conductor-bound transmission paths are manufacturer-dependent and are generally adapted to the requirements of the respective terminating unit.


Digital Interface Codes Digital Interface Codes

Signal

Clock

NRZBinary

RZBinary

AMI

HDB3

CMI

Fig. 7 Interface Codes

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HDB3-Coding rules (Third-Order-High-Density-Bipolar-Code) The HDB3-code is a modified version of the AMI-code. Binary signals or AMI-code signals may contain lengthy "0" sequences, which hinder the clock retrieval in the regenerative repeaters along digital transmission paths. The HDB3 code enables the elimination of "0" sequences with more than 3 zeros. 1. If there are more than 4 consecutive "0"-signal elements, the fourth "0"-signal

element shall be replaced by a V-signal element (= "1"-signal element) (000V). Hereby, the V-signal element takes on the same polarity as the "1"-signal element. A V-signal element causes a Violation of the AMI-rule.

2. If between the V-signal element, inserted according to the conditions specified above (rule 1), and the preceding V-signal element there is an even number of "1"-signal elements, then the first of four "0"-signal elements shall be replaced by an A-signal element (= "1"-signal element). The polarity of the A-signal element complies with the AMI rule. The last of four "0"-signal elements becomes again a V-signal element (A00V). In this case the A- and V-signal elements have the same polarity.


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VV

0 0 1 1 1 0 0 0 0 1

binary

0 HDB3

previous V-bitrule 1 appliesrule 2 does not apply

VV

0 0 1 1 0 0 0 0 0 1

binary

0 HDB3

V-bit rule 1 and 2 apply

A

previous

Fig. 8 Transformation of two binary signals into HDB3-signals


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2.1.6 Reasons for Bit Errors

The decisive quality criterion for the transmission of digital signals is the bit error rate (BER). This BER represents the proportion of bits, which have been mutilated (i.e. incorrectly recorded) during transmission, to the total amount of bits transmitted within a certain interval. The BER directly influences the quality of the transmitted services (e.g. voice channels, data channels, video signals). Two significant BER are explained exemplary in the following:

BER = 10-6 This BER virtually cannot be perceived in a voice channel. For the transmission of data channels, however, this value represents the maximum acceptable limit. The transmission system is in a state of "degraded quality", which is indicated by a degradation alarm (low priority) on the devices involved. The transmission path remains, nevertheless, in operation. BER = 10-3 This BER causes a strong interference noise in a voice channel. The operating state is judged to be of "unacceptable quality", which is signaled by the devices involved by the emission of a failure alarm (high priority). The transmission path goes out of operation.

How do bit errors arise? In the previous section it was mentioned that digital signals can be regenerated as requested, i.e. a transmission without quality reduction is possible. This statement is, however, only partially true, i.e. whenever the impairment of the transmission signals is within limits, which still permit the regeneration at the receiving side. The reasons for the formation of bit errors are

low signal/noise ratio jitter intersymbol interference

Low signal/noise proportion Noise amplitudes, which influence the amplitude decision process, are superimposed to the originally sent signal. The superimposed interference peaks lead to an incorrect signal interpretation at the receiving end. Reasons for a low S/N-ratio are:

a) too strong signal attenuation during transmission b) external interference during transmission.

For transmission in cable sections (especially optical fiber) both reasons can be largely eliminated by careful planning.


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Decision treshold

Fig. 9 Low S/N-proportion

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Jitter

Due to jitter, the transitions between signal levels log. 0 and log. 1 do not take place at periodically recurring points in time (characteristically moments) as for undisturbed signals, which means that the transitions oscillate around the characteristically moments. Jitter is characterized by jitter amplitude (unit intervals UI) and jitter frequency. One UI means that, because of deviation from the characteristically moments, the signal edges are within a range equal to the width of 1 bit. The jitter frequency is the number of oscillations around the characteristically moment per one second. Jitter influences the time decision process in the regenerator and causes bit errors for high jitter amplitudes and frequency. Jitter arises in the devices used for signal transmission (i.e. in regenerators and demultiplexers = systematically jitter), or on the transmission path due to external influences (non-systematic jitter).

Intersymbol interference Is caused by a discrepancy between the bandwidth of the transmission path and the bandwidth required for the digital signal. This leads to a bit extension, so that there is an overlap of bits, which follow each other. Thus, bit errors occur, the reasons of which can be traced back to the impairment of amplitude decision process. For conductor-bound transmission of digital signals this effect can be excluded by adequate planning. For transmission on radio paths this effect is of fundamental importance as the frequency response of the transmission path can change due to atmospherically influence.


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T

T

characteristicalmoment

signal without jitter

premature occurence of signaledge (+T/2)

late occurence of signaledge (-T/2)

Fig. 10 Representation of an Unit Interval (UI)

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85



86


2.2 Layer 2 on Abis (LAPD)


87


The layer 2 is the so-called Link Layer and uses LAPD protocol (Link Access Protocol for the D-Channel) on Abis. The main task of layer 2 is to realize a safe transmission. This is achieved e.g. by:

Introduction of a frame structure (LAPD Frames) Acknowledgement of received messages Check of counters (send and receive number) Building of checksums


88


2.2.1 Structure of a LAPD Frame (Modulo 128) on Abis

7 6 5 4 3 2 1 0 Bit-No

0 1 1 1 1 1 1 0

SAPI C/R EA

TEI EA

N(S) 0

N(R) P

opening flag

address field

control field of an

information frame

Layer 3 data(max. 260 octets)

frame check sequence

closing flag

FCS

FCS

0 1 1 1 1 1 1 0

Fig. 11 LAPD frame on Abis


89


2.2.2 Layer 2 Parameters

Opening flag / closing flag The opening / closing flag indicates the beginning / end of a LAPD frame.

EA bits In the first octet of the address field EA=0. In the second (=last) octet of the address field EA=1.

C/R bit Command/Response bit.

C=1

BTSE BSCR=1

BTSE BSC

C=0

R=0

User Side:BTSE

Network Side:BSC

ITU-TBSS

Fig. 12 Usage of the command/response bit on Abis


90


SAPI Service Access Point Identifier. The SAPI value indicates whether the signaling message is a radio signaling link message, or an O&M message, or a Layer 2 Management message.

SAPI Priority Meaning 0 2 (=low) radio signaling link

62 1 (=high) O&M messages

63 1 (=high) Layer 2 Management

It should be emphasized that the SAPI values on Abis are not the same as the SAPI values used on Um.

TEI Terminal Endpoint Identifier. With the help of the TEI, several functional same units (e.g. several TRX) can be distinguished.


91


N(S) / N(R) Send Number / Receive Number. N(S) and N(R) are counter values and allow the acknowledged transmission and reception of information frames. N(S) of the received I-frame must have the same value as the counter N(R) on the receiving side.

N(S) N(R)0→1 01 01 01 0 1 0→1 1 1 1 1

N(S) N(R)0 00 0→10 10→1 1 1 1 1 1 1 1

BTSE BSC

I-Frame N(S)=0/N(R)=0

RR-Frame N(R)=1

I-Frame N(S)=0/N(R)=1

RR-Frame N(R)=1

Fig. 13 The principle function of the counters N(S) and N(R)


92


P/F-bit Polling / Final bit. In command-frames: P/F bit = P. In response-frames: P/F bit = F. P-bit: The P-bit indicates whether or not the transmission side expects an acknowledgement on the transmitted messages, although the type of message would not require such an acknowledgement. If P=1: Frame must be acknowledged. If P=0: Frame must not be acknowledged. F-bit: If the receiving side receives a command frame with P=1, then the receive side must answer at once with a supervisory frame where F=1. FCS Frame check sequence. The FCS is used for error detection. The bits of the address field, of the control field and of the layer 3 data are taken as input of a check sequence and the result is written into the FCS field. The transmission side evaluates the FCS and sends it to the receive side. The receive side also independently evaluates the FCS and compares its value with the received value. If both values differ, a retransmission of the frame is performed.


93


Additional Remarks to the control field There are three different types of control fields:

information frames (I-frames) supervisory frames (S-frames) unnumbered frames (U-frames)

Information Frame: N(S) 0

N(R) P

The information frame always is a command and is used e.g. for the transfer of layer 3 messages.

Supervisory Frames: RR-Frame: (Receive Ready)

0 0 0 0 0 0 0 1

N(R) P/F

The receive ready frame is used e.g. to acknowledge the reception of an information frame. RNR-Frame: (Receive Not Ready)

0 0 0 0 0 1 0 1

N(R) P/F

The receive not ready frame is used to indicate an overload state to the counterpart, i.e. it is not possible for the receive side to receive further I-frames. REJ-Frame: (Reject Frame)

0 0 0 0 1 0 0 1

N(R) P/F

The reject frame is sent to indicate to the counterpart that a transmission error occurred (compare FCS) and that the I-frame has to be sent again.


94


Unnumbered Frames The length of the control field of all unnumbered frames is only one octet. SABME-Frame: (Set Asynchronous Balanced Mode Extended)

0 1 1 P 1 1 1 1

SABME-frames are sent as long as a layer 2 connection is not established. For instance, if one measures SABME-frames on Abis, this may be an indication that between the BSC and minimum one TRX there is no layer 2 connection. DM-Frame: (Disconnect Mode)

0 0 0 F 1 1 1 1

With the disconnect mode frame the send side indicates to the receive side that the layer 2 connection cannot be established any more. DM-frames will not be acknowledged. UI-Frame: (Unnumbered Information)

0 0 0 P 0 0 1 1

Unnumbered information frames are used to transport messages containing measurement results. DISC-Frame: (Disconnect)

0 1 0 P 0 0 1 1

Disconnect frames are used to clear down a layer 2 connection. The receive side must acknowledge such frames. UA-Frame: (Unnumbered Acknowledgement)

0 1 1 F 0 0 1 1

Unnumbered acknowledgement frames are used to answer to SABME-frames and to DISC-frames, that means both the establishment and the clear down of a layer 2 message are confirmed with unnumbered acknowledgement frames.


95


FRMR-Frame: (Frame Reject)

1 0 0 F 0 1 1 1

The frame reject frame is sent if protocol errors appear, i.e. a message is faulty or unexpected and indicates that the counterpart or the transmission system has problems.


96


2.3 Layer 3 on Abis


97


In I-frames and UI-frames, layer 3 information follows the layer 2 header. Depending on the SAPI value (62, 63 or 0) layer 3 uses different formats.

2.3.1 Layer 3 on RSL (SAPI 0)

Layer 3 data field

(GSM 04.08 data,

RSL)

(max. 255 octets)

Layer 2

message discriminator

message type

channel number identifier

channel number

Layer 2

Layer 3

header

Layer 3

data

field

8 bit

8 bit

8 bit

8 bit

Layer 3

Fig. 14 Layer 3 on Abis (RSL)


98


2.3.2 Layer 3 Parameters Message discriminator This 1 octet field is used to discriminate between

transparent messages non-transparent messages

and also between radio link layer messages (RLM) dedicated channel management messages (DCM) common channel management messages (CCM) TRX management messages (TRXM).

RLM:

0 0 0 0 0 0 1 T

DCM:

0 0 0 0 1 0 0 T

CCM:

0 0 0 0 1 1 0 T

TRXM:

0 0 0 1 0 0 0 T

The T-bit is set to 1 to indicate that the message is a transparent message, i.e. the message is to be considered (was considered) transparent by the BTS. The T-bit is set to 0 for non-transparent messages. RLM: Messages, which are needed for the control of a layer 2 connection between MS and BTS. DCM: Messages, which are needed for the control of layer 1 on air interface. CCM: Messages, which carry common control channel data to/from air interface. TRXM: Messages, which are needed for the TRX management.


99


Message type The message type uniquely describes the function of the layer 3 message being sent

Channel number The channel number is used to indicate the channel type (SDCCH, BCCH, ...) and the timeslot and subslot which are used on air interface for a connection.


100


2.3.3 Layer 3 on O&M Link (SAPI 62) On the O&M link manufacturer dependent solutions are visible. However, GSM 08.59 and GSM 12.21 offer some specifications. Usually during software transfer, a large amount of data must be transferred. Therefore it is necessary to segment the data and to give them a sequence number.

Layer 3 data fieldO&M dataMMI data(max. 255 octets)

Layer 2

identifier

placement

sequence number

length

Layer 2

Layer 3header

Layer 3datafield

8 bit

8 bit

8 bit

8 bit

Fig. 38 Layer 3 on Abis (O&M)


101


The identifier allows a differentiation between MMI and O&M messages. The placement parameter indicates whether or not the message consists of several segments. The sequence number allows a numbering of the single messages in case of multi-segment messages. The length parameter indicates how many useful bytes the following layer 3 data field contains.


102

A-Interface/Signaling System CCS7 SSMC Training Center

3 A-Interface/Signaling System CCS7


103

SSMC Training Center A-Interface/Signaling System CCS7


104


3.1 Signaling System CCS7


105


CCS7 stands for Common Channel Signaling system No.7. CCS7 is a signaling system employing a common channel signaling link specified by the CCITT (Committee Consultative International Telephonic et Telegraphic). The common channel signaling link is a special communication channel between functional entities, which is used specially for the exchange of signaling data. This data can be circuit-related (switching signaling e.g. ISDN-UP13) or not (transactions e.g. SCCP14, TCAP15). The CCS7 is characterized by high capacity and speed. It was originally developed for the ISDN fixed network and is also used in GSM-PLMNs between all components of the call switching subsystems SSS (i.e. on the interfaces B to G), between MSC and BSC (interface A) as well as in connections to external networks (other PLMNs, ISDN). Signaling may run via several intermediate stations. The air interface Um as well as the Abis and Asub interface have their own protocol procedure.

3.1.1 Structure of the CCS7 The signaling system CCS7 follows the OSI reference model (Reference Model of Open System Interconnection). However, instead of 7 layers as in the OSI layered model only 4 levels are specified in the CCS7. Only the first two levels of CCS7 are identical with the first two layers of the OSI model. With the CCS7 the system tasks can be divided into the levels 1-3 and the level 4: level 4 contains the task-specific user parts or user parts (UP) (comparable with

layers 4 - 7 of the OSI model), levels 1 - 3 contain the Message Transfer Part (MTP).

13ISDN-UP: ISDN user part 14SCCP: Signaling connection control part; the SCCP can also be circuit-related, e.g. in conjunction with BSSAP 15TCAP: Transaction Capabilities Application Part


106


ISDN-UPLevel 4

SCCP,Level 4

TUP,Level 4

Message transfer part

Example foruser parts

Signaling link functions, Level 2



Fig. 39 Functional levels of the CCS7

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107


3.1.2 Message Transfer Part MTP

The message transfer part MTP is a user-independent means of transport for messages between the (max. 14 defined) users and is formed from the following 3 levels:

Level 1 (physical layer) defines the physical, electrical and functional features of the signaling link, is realized by PCM30 systems or individual 64kbit/s lines (ref. to layer 1 of Abis-

Interface).

Level 2 (link layer) Level 2 of the MTP includes all functions and procedures for stable transmission of

signaling messages via a single signaling link. It thus defines the connection between two individual points of the CCS7 network and is responsible for fault detection and rectification. The individual tasks are: Error detection, i.e. checking the delimitation of the messages (flag detection),

monitoring the synchronization of the CSC16 terminal units as well as checking the contents of the received messages for transmission faults (check bits). Transmission control and reception control Link state control, i.e. monitoring and controlling the operating state of a CSC;

activation (controlled by level 3) of disturbed CSC Congestion control, i.e. monitoring the receiving memory, transmission of an

overload defense message to the partner terminal unit if necessary

Level 3 (network layer) Message routing: involves the routing of messages to the right destinations. Operates "Network management", i.e. updates information on the state of the

network, informs the user parts about the failure or re-availability of signaling connections or about overloading (MTP status message) and creates "diversions“ for the messages if parts of the network fail.

16Common Signaling Channel CSC


108


ISDN-UPLevel 4

SCCP,Level 4

TUP,Level 4

Message transfer part

Example foruser parts




Fig. 40 Functional levels of the CCS7

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109


3.1.3 User Parts UP

3.1.3.1 User Parts - General

The user parts (UP) encompass the functions, protocols and coding for signaling via the CCS7, for each user type (e.g. telephone call service, data service). The user parts control e.g. the circuit connection setup and release, the handling of services, as well as user channel administration and maintenance functions. A user part makes the following functions for the use of message transmission elements available for each defined user type: For telephone calls: Telephone User Part (TUP) For ISDN: ISDN User Part (ISDN-UP or ISUP) For signaling transactions: Signaling Connection Control Part (SCCP) For transaction processing: Transaction Capabilities Application Part (TCAP)

The following diagram shows the MTP users, as well as the relationship between one another and the MTP. The modular structure means that the CCS7 can be adapted to the set requirements; expansion for further installation is also possible. Each CCS7 user also has the option of specifying an individual user part (UP). The user part for mobile communication (MUP) is a Siemens own specification user part for the C450 mobile communication network, for example. The D900 PLMN internally uses the SCCP, and externally the ISDN UP or SCCP.


110


ISDN-UP

TCAP-user

Message transfer part (MTP)

TCAP

SCCP

CCS7 user

TUP other MTPusers

Fig. 41 Examples of user parts (UP)

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111


The protocol architecture of the central signaling channels in the GSM system or those coming from it is depicted as follows. The setup of the MTP, SCCP, TCAP, ISDN UP, MAP and BSSAP protocols is shown.


112


MTP

BSSAP MAP ISDN-UP

TCAP

SCCP

1-3

4

Fig. 42 CCS7 protocol architecture in the D900

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113


All CCS7 user parts (UP) set up on the three message transfer part (MTP) levels. The Signaling Connection User Part (SCCP) forms the basis of all user parts, with the exception of ISDN user parts. The MTP forms the basis for ISDN user parts, which can only be used alone in order to control all other applications regarding communication, within the PLMN, between different PLMNs and to the fixed network (e.g. ISDN).

3.1.3.2 User Part for the Control of Signaling Connections SCCP (Signaling Connection Control Part)

The SCCP completes the message transfer part (MTP), expands the MTP routing functions and the regulation points outside the respective signaling network and offers additional functions for message bearing. It coordinates all call paths, informs its user of CCS7 network errors (incl. subsystem errors of other exchanges) and forms the basis for all user parts (UP) in the digital switching network. The ISDN user part is an exception that can operate with, as well as without SCCP. The SCCP is established as a user part on level 4, yet it basically has level 3 functions (when compared to the OSI layer model). The SCCP forms the Network Service Part (NSP) together with the MTP. The NSP enables the user to take advantage of further message transmission functions and transmissions services, additional to the MTP functions. The supplementary transmission functions can be separated into connection orientated and connectionless, they are divided into 4 protocol classes. The user can decide on a certain data transmission method and quality with this selection of classes. The service quality increases with the selected protocol class.

Connection Oriented (CO) This function first creates a virtual signaling connection between the participating users, before transmitting their data. This corresponds to an "end to end" connection. The users determine the connection setup and release point. The messages contain a connection reference parameter with which they can be allocated to a specified virtual connection.

ConnectionLess (CL) This function enables users in different switching centers to exchange data with each other without a connection reference (physical or virtual) having to be created beforehand. Individual messages are sent via the signaling network.


114


SCCP

connection-less service

connection-oriented service

Protocolclass 0

Protocolclass 2

Protocolclass 3

Protocolclass 1

message groupswith common routing

singlemessagewithindividualrouting

signalingconnectionswithuniformrouting

signalingconnectionswithuniformrouting andmessagenumbering

Fig. 43 Protocol classes of the SCCP


115


The distinction between connectionless and connection oriented services differentiates the SCCP application cases as to their functional capability. A finer graduation is given by the so-called protocol classes. CCITT defines four protocol classes (0 to 3). The higher the protocol class, the higher the functional capacities, i.e. protocol class n+1 can do everything what protocol class n can do, and even a little bit more. The protocol classes 0 and 1 are the connectionless services, the protocol classes 2 and 3 are the connection oriented services. With protocol class 0, the SCCP only carries the information from one point to the other. The individual messages have nothing to do with each other and are routed independently to their destinations. This means that the Signaling Link Selection (SLS) is selected in such a way that the load is distributed as evenly as possible over the available signaling links. Of course, it can happen that messages overtake each other: the later dispatched message can arrive earlier if it was fortunate enough to be routed on a more suitable route. With protocol class 1, no signaling connections exist either, but the user can mark several messages as belonging together. Those messages get the same SLS so that the MTP ensures (with a high degree of probability) that they arrive in the same order in which they were dispatched. This protocol class is used at the interfaces between SSS subunits only whilst protocol class 0 is employed both at the A-interface and between the SSS subunits. With protocol class 2, the SCCP sets up and clears down signaling connections and transports messages in both directions over these signaling connections. Messages of the same signaling connection always get the same SLS so that the sequence control from protocol class 1 is ensured, too. This protocol class is used at the A-interface. With protocol class 3, additionally the messages are numbered and acknowledged within each signaling connection, so that message losses can be detected, too. This protocol class is not used for a GSM-PLMN; therefore, we shall not discuss it any more. With each signaling message, it must be clarified which protocol class it belongs to. Either the protocol class is itself transmitted as a message parameter, or it can be derived from the context.


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3.1.3.3 BSS User Part BSSAP (Base Station System Application Part) Signaling based on the BSSAP between BSS and SSS (interface A), which sets up on the SCCP and MTP functions. The function of the BSSAP is to support communication between the MSC and the BSC or TRAU. In this capacity, the BSSAP is divided into two subsystems, the BSSMAP and the DTAP. The BSSAP uses the two SCCP protocol classes 0 (connectionless) and 2 (connection-oriented). Messages, which are related to a particular RR connection at the air interface (e.g. a user connection, a Location Update, etc.), are always transmitted with protocol class 2. Messages, which do not concern a particular SCCP connection make use of protocol class 0. The SCCP connections of protocol class 2 are set up together with the RR connections. The Base Station knows the allocation between the RR connections at the air interface and the SCCP connections at the A-interface. Therefore, the BSS can forward each message it has received over an RR connection towards the MSC over the allocated SCCP connection. Vice-versa, messages the BSS has received over an SCCP connection are forwarded over the allocated RR connection towards the Mobile Station. Messages, which are exchanged in this manner between Mobile Station and MSC transparently through the BSS belong to the Direct Transfer Application Part (DTAP). The DTAP is a part of the BSSAP and consists of those messages where the layer 3 data are not modified in any way by the BSS. When the BSS receives such a message on the air interface (RR connection), it evaluates the layer 2 data, puts the layer 3 data without any alteration into an MTP-SCCP frame and transmits this frame over the corresponding SCCP connection to the MSC. When the BSS receives a DTAP message over an SCCP connection, it evaluates MTP and SCCP, puts the DTAP data without any alteration into a layer 2 frame and forwards this layer 2 frame over the corresponding RR connection to the Mobile Station. The reason for the introduction of the DTAP is that, with messages of the Mobility Management (MM) and of the Connection Management (CM), not the BSS but the SSS is affected. Only the Radio Resource Management (RR) lies within the responsibility of the BSS. Therefore, the BSS should be transparent for MM and CM. The other BSSAP messages (i.e. the messages where the BSS is not transparent) form the BSS Management Application Part (BSSMAP). With these messages, the BSS at least modifies the received information, or it is alone the sender or the receiver of these messages, respectively (e.g. the blocking of a terrestrial circuit).


117


SIEMENS D900SIEMENS D900

MSC

A- Interface

MTP

SCCP

BSSOMAP BSSAP

DTAP BSSMAP

BSS

Fig. 44 Structure of the A-interface

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118


It follows from what has been said that DTAP messages are always related to a particular RR connection; thus, they are always transmitted in protocol class 2 (connection-oriented) between BSC and MSC. The BSSMAP messages can belong to protocol class 2 as well, but there are connectionless BSSMAP messages, too (protocol class 0). All messages belong to the Common Channel Signaling System No. 7 with User Part SCCP. There are the two Application Parts BSSOMAP and BSSAP; they are distinguished in the Called Party Address of the SCCP. The BSSAP, in due course, is subdivided into DTAP (BSS is transparent for layer 3) and BSSMAP (BSS is not transparent for layer 3). The distinction between these two parts lies within the BSSAP. The DTAP messages always belong to protocol class 2, but the BSSMAP messages belong to protocol class 2 or 0. To each RR connection MS-BSS, there is an SCCP connection BSS MSC. Since the BSS is transparent for MM and CM messages, the MM and CM connections do not exist between MS and BSS but between MS and MSC.


119


BSS SIEMENS D900SIEMENS D900

MSC

CM connection

MM connection

RR connection SCCP conn.

Fig. 45 Signaling connections

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120


3.1.3.4 Transaction Capabilities Application Part (TCAP) In the GSM system the TCAP supports the mobile specific application part (MAP) and extends the functions and services of the network services part NSP (MTP + SCCP). For message transfer TCAP uses SCCP protocol classes (CL) 0 and 1.

The TCAP controls information exchange between users in different network nodes of CCS7. No circuit connections are set up.

The TCAP adds, for example, a transaction indicator to each message. This indicator makes it possible for the other party to identify the relation of all messages within one and the same transaction to an overall context. Thanks to the TCAP the MAP protocol does not need to concern itself, for example, with the interconnection of a message transfer for messages belonging to a single Location Update. Inefficiencies, which occur during transactions, are also prevented. Due to TCAP functions important data in MAP procedures (e.g. subscriber identity) need to be transmitted just once within a transaction frame. This information is valid for the remainder of the transaction.


121


MTP

BSSAP MAP ISDN-UP

TCAP

SCCP

1-3

4

Fig. 46 Protocol architecture in the D900

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122


3.1.3.5 Mobile Application Part The functions of MAP signaling procedures have a key importance within the GSM system. They affect information exchange in relation to the roaming capabilities of a mobile station (MS). In particular it controls the interrogation and updating of data in the D900 SSS specific databases VLR, HLR, EIR and AC. Examples of procedures that make it possible for a subscriber to roam within the GSM service area are: Location Registration Deletion of previous location registrations e.g. when making new location

registrations or canceling a subscription (Location Cancellation) Handling of supplementary services available to the subscriber (Handling of

Supplementary Services) Support of Short Message Service (SMS) Handling of an access request from an MS (Access Request Management) Updating of subscriber parameters in HLR and VLR MSC handover Paging and searching for the MS Transfer of confidential data for authentication and encipherment Transfer of charge information Support of different operating and maintenance functions


123


MTP

BSSAP MAP ISDN-UP

TCAP

SCCP

1-3

4


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124


3.1.3.6 ISDN User Part (ISUP) ISUP provides the respective signaling capabilities for basic bearer and supplementary services. Signaling can occur either link-by-link or end-to-end. In general the ISUP is comprised of the signaling function for the control of the setup and release of call connections (digital / analog

subscribers) management of trunk lines handling of services and service aspects (e.g. display of A subscribers CLIP,

Closed User Group CUG, call holding HOLD,...) The ISUP is also able to utilize SCCP services although this is not necessary.


125


MTP

BSSAP MAP ISDN-UP

TCAP

SCCP

1-3

4


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126



127


3.2 Formatting Rules


128


The BSSAP is always transmitted in the SCCP parameter "Data". This is an optional parameter in the SCCP messages "Connection Request" (CR),

"Connection Confirm" (CC) and "Released"(RLSD) a mandatory parameter of variable length in the SCCP messages "Data Form 1"

(DT1) and "Unitdata"(UDT). CR, CC, RLSD and DT1 are messages of the protocol class 2 (connection-oriented) whilst UDT belongs (at the A-interface) to the protocol class 0 (connectionless). Because "Data" can appear as an optional parameter or as a mandatory parameter of variable length, the SCCP always contains a length indicator for the "Data" field, which gives the total length of the BSSAP. After this length indicator, the so-called Discrimination byte follows which distinguishes between DTAP and BSSMAP. The most significant seven bit are 0, and the least significant bit (= the discrimination bit) is 1 for the DTAP (i.e. transparent) and 0 for the BSSMAP (i.e. not transparent).


129


Optional

in CR, CC and RLSDMandatory

in UDT and DT1

SCCP message type: UDT, DT1

Mandatory parametersof fixed lengt

Mandatory parametersof variable lengt

P o i n t e r: D a t a

L e n g t h i n d i c a t o r

D i s c r i m i n a t i o n B y t e

B S S A P

Optional parameters

SCCP message type: CR, CC, RLSD

Mandatory parametersof fixed lengt

Mandatory parametersof variable lengt

Optional parameters

I d e n t i f i e r : D a t a

L e n g t h i n d i c a t o r

D i s c r i m i n a t i o n B y t e

B S S A P

Fig. 49 Embedding of the BSSAP into the SCCP


130


In the case of the DTAP, after the Discrimination byte the Data Link Connection Identification (DLCI) ensues which is also 1 byte long. The byte indicates the SAPI (Service Access Point Identifier, from layer 2 of the air interface) with which the message has been received or is to be sent, respectively. After the DLCI, the following data ensue: the length indicator for layer 3 of the air interface (1 byte) layer 3 of the air interface corresponding its formatting rules .

The value of the SCCP length indicator for the "Data" parameter exceeds by 3 the length indicator for layer 3 since the "Data" length indicator includes three additional bytes (the discrimination byte, the DLCI and the length indicator for layer 3). In the case of the BSSMAP, the following data ensue after the discrimination byte: the length indicator for layer 3 of the BSSMAP layer 3 of the BSSMAP itself.

This time, the two length indicators ("Data" parameter, layer 3 BSSMAP) differ by 2 only since the DLCI byte is omitted. Layer 3 of the BSSMAP consists of information elements. The first information element (after the length indicator) is the message type. It has a length of 1 byte and classifies the messages as to their purpose (e.g. "Assignment Request", "Complete Layer 3 Information" etc.). The GSM guideline 08.08 contains, for each message type, a list of the further information elements of the message; these further information elements can be optional (O) or mandatory (M). However, the elements always begin with an element identifier with the length of 1 byte. Thus, the only element without an element identifier is the message type itself. Simultaneously, the list of information elements indicates the sequence in which the mandatory and optional parameters (the latter as far as present) must be sent. There is no general rule for this sequence; rather, it is defined for each message type individually.


131


0 0 0 0 0 0 0 0Length indicator

BSSMAP message type

information elements

(always with identifier)

Discriminator:not transparent

DTAP:

BSSMAP:

Discriminator:transparentDLCI

0 0 0 0 0 0 0 10 0 0 0 0

Layer 3 of theair interface

SAPILength indicator

Fig. 50 Layout of DTAP and BSSMAP (GSM 08.06)


132


Elements of variable length contain after the identifier a length indicator of 1 byte, which indicates how many bytes will follow after the indicator. The total length of such an element is the length indicator value +2 (since the length indicator does not count the identifier and itself). With elements of fixed length, the length indicator is omitted; here, after the identifier, the contents begin immediately. Let's consider as a first example the message "Block" which is used by the BSC to inform the MSC that it cannot access a certain terrestrial circuit any longer (see the BSSMAP procedure "blocking"). Besides the message type, the message contains two more parameters: the Circuit Identity Code (CIC) of the affected channel and the cause for the blocking (e.g. "Equipment failure" or "OAM intervention"). Both parameters are mandatory. Whilst the CIC has the fixed length of 3 byte, the cause can have a length of 3 or 4 byte; thus, the indication of the length in the message is necessary. "Block" is always transmitted in a "Unitdata" (UDT). Therefore, "Data" is a mandatory SCCP parameter of variable length. As a second example, we take the message "Complete Layer 3 Information" which is used by the BSC to set up the SCCP connection. This message belongs to the BSSMAP procedure "Initial MS message". A layer 3 message of the air interface received in an SABM is forwarded to the MSC; the BSC adds the identity of the radio cell. Correspondingly, the message contains, besides the message type, the cell identity and the layer 3 data of the air interface. Both parameters are mandatory and have a variable length. As a consequence, length indicators are required. The optional parameter chosen channel tells which channel was selected at the air interface. "Complete Layer 3 Information" is always transmitted in a "Connect Request" (CR). Thus, "Data" is an optional SCCP parameter.


133


Information element Type Length

Message Type M 1

Circuit Identity Code (CIC) M 3

Cause M 3-4

Fig. 51 Complete layer 3 information

Information element Type Length

Message Type M 1

Cell Identity M 3-10

Layer 3 information M 3-n

Chosen Channel 0 2

Fig. 52 Complete layer 3 information


134


As an example for a DTAP message, we select the "Setup" MS → BSS → MSC. The BSS removes the layer 2 frame of this message and adds instead the Discrimination byte (0000 0001 = transparent, i.e. DTAP) the DLCI (Data Link Control Identifier). The last 3 bit provide the SAPI value 000

(signaling) the length indicator of layer 3 (here: 17 byte).

The layer 3 data with protocol discriminator, transaction identifier, message type and all information elements are forwarded to the MSC in an unaltered manner. The DTAP message constructed in this way is contained in an SCCP message "Data Form 1" (DT1) as parameter "Data".


135


Discrim.:transparent

DLCI: SAPI = 0 (signaling)

Length indicator: 17 Byte

Protocol discriminator CC (TI-Flag = 0)

Message Type etup�凷

Bearer Capability:Length 1,speech full rate, Circuit Mode

Called Party BCD Number:Length 7,Type of Number unknown,Numbering Plan unknown,Number 08972241497

Low Layer Capability:Length 1,speech

0 1 0 1 1 1 1 0

0 0 0 0 0 0 0 1

0 0 0 1 0 0 0 1

0 0 1 1TI-Value0

0 0 0 0 0 1 0 0

0 0 0 0 0 0 0 1

1 0 1 0 0 0 0 0

0 0 0 0 0 1 1 1

1 0 0 0 0 0 0 0

0 1 1 1 1 1 0 0

0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0

0 0 0 0 0 1 1 1

0 0 00 0 0 0 0

0 N(SD) 0 0 0 1 0 1

01 0 0 0 0 0 0

1 0 0 110 1 1

00 1 0 00 1 0

00 0 1 10 0 0

01 0 1 10 0 0

11 1 1 10 1 1

Fig. 53 Example for a DTAP message


136


Now, we consider an example for a "Block" message. The message begins with the Discriminator byte 0000 0000 (not transparent, i.e. BSSMAP). There now follows the length indicator (here: 7 byte). The subsequent message type 0100 0000 identifies the message as "Block". Afterwards, the CIC must ensure. Indeed, we find next the element identifier 0000 0001, which marks the next element as CIC, followed by 2 bytes CIC value. Here, the length is fixed, and no length indicator is included. Now, we find the element identifier 0000 0100, i.e. Cause. This time, a length indicator is required since the total length can vary. The length indicator has the value 1 (1 byte contents), and we conclude 3 bytes total length of the element (1 byte identifier, 1 byte length indicator, 1 byte contents). The content of the element "Cause" begins with an extension bit (value 0: no further byte present). The next 3 bits identify the class of the cause (value 010: resource unavailable), whilst the next 4 bits clearly identify the cause within its class (here: equipment failure). "Block" is a "Data" parameter in the SCCP message "Unitdata" (UDT).


137


0 0 0 0 0 0 0 0

0 0 0 0 0 1 1 1

0 1 0 0 0 0 0 0

0 0 0 0 0 0 0 1

CIC

0 0 0 0 0 1 0 0

0 0 0 0 0 0 0 1

0 0 1 0 0 0 0 0

Discrim.: not transparent

Length indicator: 7 byte

Message Type Block

Element identifier Circuit Identity Code

Element identifier Cause

Length 1

Equipment Failure

Fig. 54 Example for a "Block"

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


138


As last example, we consider a "Complete Layer 3 Information" where the layer 3 message "Location Update Request" is embedded. The message begins with the Discriminator byte 0000 0000 (not transparent, i.e. BSSMAP), and the length indicator ensues (here: 23 bytes). The next byte with the value 0101 0111 identifies the BSSMAP message as "Complete Layer 3 Information". The first parameter is the cell identity, which is marked by the identifier value 0000 0101. The next byte says that 3 bytes for the contents are going to follow; thus, the total length of the element is 5 bytes. Next, a discriminator follows which indicates which cell characteristics are contained in the element. The value 0000 0010 means that the cell is identified by the Cell Identity CI alone (and not by LACOD+CI or even by CGI = MCC+MNC+LACOD+CI). Accordingly, two bytes CI-value ensue. The next - and last - parameter is the layer 3 information, marked by the identifier 0001 0111. The length indicator states that the layer 3 data have a length of 15 bytes; a total length of 17 bytes results. There now follows the "Location Update Request" with protocol discriminator, transaction identifier, message type and all information elements. This BSSMAP message is a "Data" parameter in a "Connect Request" (CR) from the Base Station to the MSC.


139


0 0 0 0 0 0 0 10 0 0 1 0 1 1 1

0 1 0 1 0 1 1 10 0 0 0 0 1 0 1

0 0 0 0 0 0 1 10 0 0 0 0 0 1 1

CI

0 0 0 1 0 1 1 10 0 0 0 1 1 1 1

Key Sequ. Nr.MCC

1 1 1 1MNC

LACOD

RF Power

0 0 0 0 0 1 0 1

TMSI

Location Area Identification

Mobile Identity:Length 5; TMSI

Mobile Station Classmark 1

Element identifier Layer 3 information

Length 15 byte

Protocol discriminator MM (TI=0)

Message Type �Loc. Update Request“

Normal Loc. Upd.; no follow-on

Discrim.: not transparent

Length indicator: 23 byte

Message type Complete Layer 3 inform.

Element identifier Cell identity

Length 3 byte

Cell identified by CI

0 1N(SD) 0 0 0 0 0

0 0 0 0 0 1 0 1

0 0 0 0

0 0 0 0 0

1 1 1 1 0 1 0 0

Fig. 55 Example for a "Complete Layer 3 Information"


140



141


3.3 Appendix


142


Simplified, it can be said that the BSS tries as far as possible to deal by itself with the proceedings at the air interface, whereas the SSS is in charge of all proceedings between MSC and BSC and, of course, within the SSS itself. Thus, the user channels at the A-interface are always seized and released by the MSC; the BSC can only indicate if a channel is blocked. On the other hand, all channels of the air interface are administered by the BSC. Here, the MSC can only initiate the channel release (during call clear down, Handover etc.). Handover within one cell or within the BSC area is controlled by the BSC, but as soon as the BSC area is left, the MSC is in charge, of course. Finally, the BSC enciphers and deciphers the radio channels, but it gets the ciphering key from the MSC.


143


Terrestrial channel: Channel AllocationTerrestrial channel: Blocking indicationRadio channel: ConfigurationManagenemtRadio channel: Frequency hoppingManagementRadio channel: Idle channel ObservationRadio channel: Power controlTCH: Channel Allocation (Choice)TCH: Link SupervisionTCH: Channel ReleaseBCCH/CCCH: Scheduling of MessagesDCCH: Link SupervisionDCCH: Channel ReleaseDCCH: AllocationRadio Ressource Indication (report idlechannels)Channel CodingTranscoding/Rate AdaptationInterworking Function (data calls)Measurements: Reported from MSMeasurements: UplinkMeasurements: TrafficHandover: within one cellHandover: within the BSCHandover: external; Recognition RadioReasonHandover: external; Recognition TrafficReasonHandover: external; DecisionHandover: external; ExecutionMM: AuthenticationMM: Location UpdateMM: PagingCall ControlUser Data EncryptionSignaling Element Encryption

XX

X

XXXXXXXXXX

XX

XX

XXX

X

X

XX

X

X (Invoked by MSC)

X (Invoked by MSC)

MSC defines Call Type

X

XMSC informedMSC informed

X

XXXXXX

Key / Algorithms from MSCKey / Algorithms from MSC

Function BSS SSS

Fig. 56 BSS - SSS function split (GSM 08.02)


144


3.3.1 BSSMAP-Procedures Fig. gives an overview over all the procedures of the BSSMAP and their distribution over the SCCP protocol classes 0 (connectionless) and 2 (connection-oriented). It can be seen that all proceedings related to an existing user connection belong to class 2 whilst global procedures such as blocking and releasing of circuits are executed in class 0. The set up of SCCP connections is performed by the BSSMAP, too. This can be caused by the BSC and by the MSC as well. When a Mobile Station sets up a new RR connection at the air interface, e.g. for a mobile originating or terminating call, or for a location update, the Base Station reacts by setting up the SCCP connection to the mobile switching center. This is the BSSMAP procedure "Initial MS message". When, on the other hand, a Handover to a new BSC is executed, it is the MSC which sets up the SCCP connection. This is done in the BSSMAP procedures "Handover resource allocation" and "Handover execution".


145


Procedure Class 0 Class 2

Initial MS message

Assignment

Release

Cipher mode control

Paging

Handover required indication

Handover resource allocation

Handover execution

Classmark update

Trace invocation

Queuing indication

Data link control for SAPI ≠ 0

Blocking

Resource indication

Reset

Reset Circuit

Handover candidate enquiry

Flow control

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Fig. 57 BSSMAP procedures (GSM 08.08)


146

Signaling Sequences SSMC Training Center

4 Signaling Sequences


147

SSMC Training Center Signaling Sequences

4.1 Complete Call Sequences 4.1.1 Location Update

SDCCH

BSS MSC

RACH

AGCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

Authentication Response (SRES)

UI (Imm. Assign.)

SABM(Loc. Upd. Req.)

Authentication Request (RAND)

Channel Req.

UA

I (Ciph. Comm.)

SDCCH I (Ciph. Compl.)

TMSI Reallocation Complete

Location Update Accept

I

I

I

I

I (Channel Rel.)

DISC

UA

CR (Complete L3 Info)(Cell-Id., Loc. Upd. Req.)

CC

DT1

DT1

DT1 (Clear Command)

DT1 (Clear Compl.)

DT1 (Cipher Command)

DT1 (Cipher Compl.)

DT1

DT1

RLSD

RLC

Fig. 58 Location update


148


4.1.2 Mobile Originating Call (MOC)

SDCCH

BSS MSC

RACH

AGCH

SDCCH

SDCCH

SDCCH

FACCH

FACCH

Authentication Response (SRES)

UI (Imm. Assign.)

SABM(CM Request)

Authentication Request (RAND)

Channel Req.

UA

I (Ciph. Comm.)

SDCCH I (Ciph. Compl.)

and so onSet up

I

I

I

I (Ass. Command)

SABM

UA

CR (Complete L3 Info)(Cell-Id., MOC.)

CC

DT1

DT1 (Assign Request)


DT1 (Cipher Compl.)

DT1

DT1

DT1 (Assign Complete)FACCH I (Ass. Complete)

Fig. 59 Mobile Originating Call (MOC)


149


4.1.3 Mobile Terminating Call (MTC)

SDCCH

BSS MSC

PCH

RACH

AGCH

SDCCH

FACCH

UI (Paging Req.)

SABM(Paging Resp.)

UI (Imm. Assign.)

UA

SDCCH

Authentication Request (RAND)I

I (Ciph. Comm.)

I (Ciph. Compl.)

CR (Complete L3 Info)(Cell-Id., MTC.)

CC

DT1


DT1 (Cipher Compl.)

UDT (Paging)

Authentication Response (SRES)I DT1

Set up

and so on

Channel assignment as with Mobile Originating Calls

I DT1

Fig. 60 Mobile Terminating Call (MTC)


150


4.1.4 Call Clear Down

FACCH

BSS MSC

Disconnect

Release

UA

I

I

RLSD

DT1

DT1

Initiated by the mobile station:

Release CompleteI DT1

FACCHI (Channel Rel.) DT1 (Clear Command)

FACCH DISC DT1 (Clear Complete)

RLC

FACCH

BSS MSC

Disconnect

Release

UA

I

I

RLSD

DT1

DT1

Initiated by the partner side:

Release CompleteI DT1

FACCHI (Channel Rel.) DT1 (Clear Command)

FACCH DISC DT1 (Clear Complete)

RLC

FACCH RR

Fig. 61 Call clear down


151


4.1.5 Differences between Important Complete Call Sequences

The following table will give you an overview in an abstract form about differences between mobile originated call (MOC), mobile terminated call (MOC) and Location Update (LOCUPD).

Differences between important complete call sequences: Message / Procedure MOC MTC LOCUPD Paging Message X

Immediate Assignment Procedure X X X

Security Procedures * (Authentication, Identity check, Ciphering)

X X X

Setup Message X X

Locupd accept Message X

TMSI Reallocation Message* X X X

Assignment Procedure X X

Alert, Connect, Connect Acknowledge Messages X X

Disconnect, Release, Release Complete Messages X X

Clearing Procedure X X X * These procedures are not always done. It can be administered in the Siemens MSC how often these procedures should be executed.


152


4.2 Message Flow of Basic Circuit Switched BSS Procedures

The scanners gather data by adapting the counters assigned to them at certain events. These events are messages, which are exchanged between the network elements (NE) on different occasions (call setup, handover, location update etc.).This chapter describes the most important procedures used on the BSS Interfaces.

4.2.1 Immediate Assignment Procedure The immediate assignment procedure is used to create a signaling connection between the MS and the network. It can be initiated only by the MS. The reason for this may be:

response to a PAGING REQUEST message location update call setup etc.

With a CHANNEL REQUEST message on the RACH the MS signals the BTS that it requires a signaling channel (SDCCH). This message contains the information field „establishment cause and random reference“. The „establishment cause“ gives the reason why the MS is requesting a SDCCH. Possible reasons are:

emergency call call re-establishment answer to paging originating speech call originating data call location updating other procedures, which can be completed with an SDCCH.


153


The BTS forwards the request to the BSC with a CHANNEL REQUIRED message. The BSC selects a free SDCCH and instructs the BTS with a CHANNEL ACTIVATION message to activate it. If the SDCCH is successfully activated, the BTS responds with a CHANNEL ACTIVATION ACKNOWLEDGE message. If not, it sends a CHANNEL ACTIVATION NEGATIV ACKNOWLEDGE message. Channel activation may fail for the following reasons:

O&M intervention (channel blocked) channel already occupied hardware fault.

The BSC then sends to the BTS an IMMEDIATE ASSIGNMENT COMMAND message, which is forwarded to the MS, to instruct the MS to activate the channel. In case of a failure the BSC sends an IMMEDIATE ASSIGNMENT REJECT message to the BTS and further on to the MS. If the BTS is not able to send the IMMEDIATE ASSIGNMENT message due to the Access Grant Channel (AGCH) being overloaded, it notifies the BSC of this with a DELETE INDICATION message. When the MS receives the IMMEDIATE ASSIGNMENT message, it switches to the assigned channel and activates it. By sending an SABM frame containing a „Service Request Message“, it switches the SDCCH to the „Multiple Frame Acknowledge“ mode, there by activating it. The Service Request message helps the network to recognize the service being requested by the MS. This information is used to decide how to proceed. Service request messages are:

CM SERVICE REQUEST LOCATION UPDATING REQUEST IMSI DETACH PAGING RESPONSE CM REESTABLISHMENT REQUEST

The BTS sends confirmation to the MS, that it has received the service by means of a UA frame. The BTS also informs the BSC with an ESTABLISH INDICATION message, which also contains the service request message. Further coordination procedures (authentication, ciphering etc.) are now performed on the SDCCH.


154


IMMEDIATE ASSIGNMENT PROCEDURE

MS BTS BSC

CHANNEL REQUEST

CHANNEL REQUIRED

(NATTSDPE, NACSUCPR, ATIMASCA,ASDCALTI, ATSDCMBS, NINVRACH)

CHANNEL ACTIV

CHANNEL ACTIV ACK

CHANNEL ACTIV NEG. ACK

IMMEDIATE ASS CMD

IMMEDIATE ASS REJECT

(TACCBPRO, SUIMASCA, NACSUCPR)

DELETE INDICATION

IMMEDIATE ASS CMD

IMMEDIATE ASS REJECT

SABM

UAESTABLISH INDICATION (*)

(NSUCCHPC, NASUSDPE)

(NACSUCPR)

*CM Service Request, Locupd Request,Paging Response

Fig. 62 Immediate assignment procedure


155


4.2.2 Paging Procedure

The paging procedure is used to inform the mobile station (MS) that a connection setup is being requested. In case of a mobile terminated call the MSC/VLR, has to send a PAGING message to all BSC belonging to the location area, where the MS is located. The PAGING message, contains the temporary mobile station identity (TMSI) and the location area of the MS. This message can be repeated after a certain time (MSC Timer value, e.g. 8s ) containing now IMSI and TMSI, if there was no response. All involved BSC then generates a PAGING COMMAND message, which will be transmitted to all the BTSs in the location area. If a BTS gets a PAGING COMMAND message, it transmits a PAGING REQUEST message on the paging channel (PCH). The PAGING REQUEST message contains the TMSI (IMSI). A MS which receives a PAGING REQUEST message, checks whether the received TMSI / IMSI is identical with the TMSI (IMSI) on the SIM card. If this is the case, it initiates an „immediate assignment“ procedure (-> 3.1) to occupy an SDCCH. If the SDCCH was occupied, the BSC sends a CONNECTION REQUEST including the COMPLETE LAYER 3 INFORMATION message to the MSC. If the MSC/VLR has lost the LAC of a MS, then the Searching Procedure is used instead of the paging procedure. Then the PAGING message is sent to all cells of the MSC/VLR area. If the MS is attached in the network a Periodic Location Update is done periodically. The time can be administered in the BSC. The Detach Time, to detach the MS in the MSC/VLR, has however to be administered in the MSC. The following rule has to be valid, that a mobile terminating call is always possible. Detach Timer (MSC) > Periodic Location Update Timer (BSC).


156


MS BTS BSC MSC

PAGING PROCEDURE

IMMEDIATEASSIGNMENT

PAGINGPAGING COMMAND

PAGING REQUEST

CHANNEL REQUIRED

(NATTSDPE, NACSUCPR,ATIMASCA, ASDCALTI,

ATSDCMBS)CHANNEL REQUEST

CHANNEL ACTIV

CHANNEL ACTIV ACK

IMMEDIATE ASS CMD

(TACCBPRO, SUIMASCA,NACSUCPR)

CR (COMP LAYER3INFO (PAG RES))

ESTABLISH INDICATION(NSUCCHPC)

(TACCBPRO)

IMMEDIATE ASS CMD

UA(PAGING RESPONSE)

SABM(PAGING RESPONSE)

Fig. 63 Paging procedure


157


4.2.3 Assignment Procedure

The assignment procedure is used to occupy a radio resource (e.g. speech channel/data channel), if it is required. The MSC is Initiator of this procedure (except in case of intracell Handover). The MSC sends an ASSIGNMENT REQUEST message to the BSC requesting the assignment of a radio resource (RR). The ASSIGNMENT REQUEST message contains information on the requested channel (channel type (speech/data), priority, interference band to be used etc.), which is to be evaluated by the BSC. Based on this data, the BSC selects a suitable RR and activates it, with the message CHANNEL ACTIVATION. If the SDCCH is successfully activated, the BTS responds with a CHANNEL ACTIVATION ACKNOWLEDGE message. If not, it sends a CHANNEL ACTIVATION NEGATIV ACKNOWLEDGE message and furthers on to the MSC an ASSIGNMENT FAILURE message. Channel activation may fail for the following reasons:

O&M intervention (channel blocked) channel already occupied hardware fault.

It then instructs the MS with an ASSIGNMENT COMMAND message to occupy the channels. When the MS receives the ASSIGNMENT COMMAND message, it switches to the assigned channels and activates them by sending an SABM frame. The BTS acknowledges receipt of the SABM frame with a UA frame to the MS and informs the BSC with an ESTABLISHMENT INDICATION message that the MS has occupied the channels. When the MS receives the UA frame, it sends an ASSIGNMENT COMPLETE message to the BSC. If the assignment procedure was initiated by the MSC (the BSC can also initiate the procedure independently for an intracell handover), the BSC informs the MSC with an ASSIGNMENT COMPLETE message that the procedure has been successful.


158


MS BTS BSC MSC

ASSIGNMENT PROCEDURE

ASSIGNMENT REQUEST

CHAN ACTIV

ASSIGNMENT COMMAND

CHAN ACTIV ACK

SABM

CHANNEL ACTIV NEG ACK

ASSIGNMENT COMMANDASSIGNMENT FAILURE

ASSIGNMENT COMPLETE

(TASSFAIL)

UA

ASSIGNMENT COMPLETE

ESTABLISH INDICATION(TNTCHCL)

ASSIGNMENT COMPLETE

(TASSATT, ATTCHSEI,AALTCHTI, ATCHSMBS,MBTCHAMR)

(TASSSUCC, SUCTCHSE)

PHYS CONTEXT REQ

PHYS CONTEXT CONF

(MTCHBUTI)

Fig. 64 Assignment procedure


159


4.2.4 Clearing Sequence

The clearing sequence is used to release radio resources and associated terrestrial channels. There are many reasons to start the clearing sequence, as normal clearing, radio failure, connection failure, protocol error, etc. After the BSC acknowledges with a RELEASE COMPLETE message, that a channel has to be released, the MSC starts the Clearing Sequence by sending of a CLEAR COMMAND message. The BSC instructs the MS to release the occupied mobile channels with a CHANNEL RELEASE on the FACCH. A DEACTIVATE SACCH message is also sent to the BTS to deactivate the signaling channel. After receiving of the CHANNEL RELEASE message the MS starts to deactivate the channel and sends a DISCONNECT message to the BTS. After receiving of the DISC message the BTS deactivates all the channels connected to the MS. To acknowledge the deactivation of the channels, the BTS sends a UA frame to confirm the DISC message. After receiving the UA frame the MS releases all the remaining channels and goes into “idle mode“. The BTS also informs the BSC with a RELEASE INDICATION message that all remaining channels of the MS are now released. The BSC instructs the BTS with a RF CHANNEL RELEASE message to release the channels already deactivated by the MS. After release, the BTS acknowledges this with an RF CHAN REL ACKNOWLEDGE message. At the end of this procedure the BSC sense a CLEAR COMPLETE message to the MSC to indicate, that the Clearing Sequence was successful. A clearing sequence can be triggered e.g. by the call ending as normal, as handover, the end of a location update or the aborting of a connection. In the latter case the BSC is informed of this by a CONNECTION FAILURE INDICATION message sent by the BTS and further on to the MSC to start the Clearing Sequence.


160


MS BTS BSC MSC

CLEARING SEQUENCE

DT1 (**)DATA IND (**)

CHAN REL

DATA REQ (RELEASE)

DISC

DATA IND (REL CMP)

DATA REQ (CHAN REL)

DT1 (CLEAR COMPLETE)

REL INDICATIONUA

DATA IND (*)

DEACT SACCH

RLSD

(NRFLTCH, NRFLSDCC)

RF CHAN REL ACK

RF CHAN REL

* DISCONNECT (Normal Clearing)** DISCONNECT (Normal Clearing)

ERROR INDICATION (Cause)CONN FAILURE INDICATION

(Cause)

DT1 (RELEASE)

DT1 (REL CMP)

DT1 (CLEAR COMMAND)

RLC

T3110

T3109

T3111

T1

CLEARINGSEQUENCE

I (RELEASE)

I (REL CMP)

(MTCHBUTI, AALTCHTI)

Fig. 65 Clearing sequence


161


Timer In the Clearing Sequence the Timer are used to supervise the release of channels. It must be sure, that in any case, first the Mobile has to release all channels and than the BTS. This is necessary, that in case of a new call setup, 2 Mobiles are not synchronized to the same channel.

T3109 Start: DATA REQUEST (CHANNEL RELEASE) message Stop: DISCONNECT message Expiry: BSS deactivates all channels for this MS Default: 12 seconds.

T3110 Start: CHANNEL RELEASE message Stop: UA frame Expiry: MS deactivates all channels Default: 1.5 seconds.

T3111 Start: RELEASE INDICATION message Stop: RF CHANNEL RELEASE message Expiry: BSS deactivates all channels for this MS Default: 0.5 seconds

T1 Start: RF CHANNEL RELEASE message Stop: RF CHANNEL RELEASE ACKNOWLEDGE message Expiry: BSC marks the belonging circuits as blocked Default: 6 seconds


162


4.2.5 Kind of Handover The following table will give you an overview about the different kind of handover and the related SBS Counter.

Counter/ INTRA MSC HOV INTER MSC HOV

Kind INTRA BSC INTER BSC INTER BSC of Handover INTRA CELL INTER CELL INTER CELL INTER CELLAttempted Handover

ATINHIAC (C,CA) AISHINTR (C)

ATINHIRC (C,CA) AOUINIRH (NO,CA)AININIRH (NI) AISHINTE (C)

ATINBHDO (NO, CA) AOINTESH (C)

Successful Handover

SINTHITA (C,CA) SINHOBSC (B,CA) SISHINTR (C)

SINTHINT (C,CA) SINHOBSC (B,CA) SOUINIRH (NO,CA)SININIRH(NI) SISHNTE (C)

SUINBHDO (NO, CA) SOINTESH (C)

Unsuccessful Handover without loss of call / SDCCH

UNINHOIA (C,CA) UISHINTR (C)

UNINHOIE(NO,CA) HOFITABS (B) UISHINTE (C)

NRUNINHD (NO,CA) NRINHDFL (BI) UOINTESH (C)

Unsuccessful Handover with loss of call / SDCCH

UNIHIALC (C) UNIHIRLC (C)

Overview Kind of Handover

The text in brackets has the following meaning:

B = per BSCBI = per BSC incomingC = per cellNO = per neighbor cell outgoing NI = per neighbor cell incoming CA = per causeNote: To let the handover work cell parameters have to be defined in the BSC (LAC, CI, BSIC, ...) and also in the MSC (LAC, CI). For Inter MSC Handover the Anker LTG will take control of the call, also if there will be several Inter MSC Handover, Therefore also the External Location Area Codes (EXTLAC) of all MSC should be defined.


163



164


4.2.5.1 Intracell Handover If the BTS notices from the MEASUREMENT REPORT messages periodically being received from the MS, that the quality of the Tch connection is decreasing with a constant receive level, it introduces an intracell handover with an INTRA CELL HO CONDITION INDICATION message to the BSC. This message can also be sent from the BTS to the BSC in case of intracell handover due to other procedures like the Adaptative Multirate -, the enhanced pairing - or also the forced intra cell handover to a preferred TRX procedure. The procedure for the SDCCH intra cell Handover is described in the SBS Message Flows Document (See appendix). The BSC selects a suitable RR and activates it, with the message CHANNEL ACTIVATION. If the TCH is successfully activated, the BTS responds with a CHANNEL ACTIVATION ACKNOWLEDGE message. The BSC instructs the MS with an ASSIGNMENT COMMAND message on the old channel to switch to the new one. If the MS receives the ASSIGNMENT COMMAND message, it releases the connection on the old channels, switches them to the new ones and activates them. After occupying the new channels the MS replies with an ASSIGNMENT COMPLETE message. When the ASSIGNMENT COMPLETE message is received, the BSC releases the old channels. If the BSS assigns a frequency to the MS, which it does not support, the MS sends an ASSIGNMENT FAILURE message and remains on the old channels. If the “Channel Mode“ requested by the BSS is not supported, the MS sends also an ASSIGNMENT FAILURE message and remains on the old channels. The BSC informs the MSC that an intra-BSC handover has been performed with a HANDOVER PERFORMED message.

Timer In the INTRA CELL Handover Procedure the Timer are used to supervise the channels. The BSS must keep the old channel as long until the MS has occupied the new one. The Mobile must have the possibility to go back to the old channel.

T10 Start: ASSIGNMENT COMMAND message Stop: ASSIGNMENT COMMAND COMPLETE message Expiry: BSS releases the new and the old channels The connection to the MS is lost Default: 5 seconds.


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MS BTS BSC MSC

INTRACELL HANDOVER

INTRA CELL HO COND IND

ASS COMMAND(OLD CHANNEL)

CHAN ACTIV

SABM

CHAN ACTIV ACK

ASS COMMAND(OLD CHANNEL)

ASS COMPLETE(NEW CHANNEL)

UA

MEAS REP

ESTABLISH INDICATION

(AALTCHTI, ATTCHSEI,MBTCHAMR)

HANDOVER PERFORMED

T10

MEAS REP

ASS COMPLETE(NEW CHANNEL)

ASS FAILUREASS FAILURE

(SUCTCHSE,NASUSDPE)

(MTCHBUTI)

(TNTCHCL)

(SINTHITA, SINHOBSC,SISHINTR)

(UNINHOIA,UISHINTR)

(UNIHIALC)

(ATINHIAC,AISHINTR)

Fig. 66 Intracell handover


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4.2.5.2 Intercell Handover, Intra-BSC If during a connection the BTS notices from the values periodically transmitted by the MEASUREMENT REPORT messages, that the previously set threshold values for quality (RXQUAL), reception level (RXLEV), better cell or distance have been reached, the BTS decided to do a Handover. Therefore the BTS reports this to the BSC with a HANDOVER CONDITION INDICATION message. The BTS keeps a Target Cell List, which it uses as a basis to decide whether an inter-cell or an intra-cell handover is required. If the first cell on the list is in same BSC area, the BSC selects the first cell from the list, selects a suitable RR for the new BTS and activates it, with the message CHANNEL ACTIVATION. If the TCH is successfully activated, the BTS responds with a CHANNEL ACTIVATION ACKNOWLEDGE message. The BSC send a HANDOVER COMMAND message to the BTS and further on to the mobile station (MS), which contains information about the new cell and channels. With a HANDOVER ACCESS message, which can be repeated twice, the mobile station occupies the new channels it has been assigned in the target cell. If the new BTS receives the Handover Access message, it indicates the BSC, that it can see the mobile station. The BTS synchronized on the new TRX and transmits a PHYSICAL INFORMATION message to the mobile station. The mobile station replies to the PHYSICAL INFORMATION message with a HANDOVER COMPLETE to the new BTS. The HANDOVER COMPLETE message is forwarded to the BSC. The BSC indicates to the MSC with a HANDOVER PERFORM message that there was a successful Handover. If Timer 3124 in the MS expires, before the MS receives a PHYSICAL INFORMATION message from the BTS, it reverts to the old channels and sends a HANDOVER FAILURE message over the old channels to the BSC. The BSC then starts the clearing sequence to release the new channels. Other reasons for the failure of a handover may be for example:

the BSC assigns a new channel whose mode is not supported by the MS. the BSC assigns a new frequency to the MS, which the MS does not support.

“Synchronous“ or “pseudo-synchronous“ handovers, where the PHYS INFO message is not necessary, are not currently supported.


167


Timer In the Intra BSC Handover Procedure the Timer are used to supervise the channels. The BSS must keep the old channel as long until the MS has occupied the new one. The Mobile must have the possibility to go back to the old channel.

T3124 Start: HANDOVER ACCESS message Stop: PHYSICAL INFORMATION message Expiry: MS reverts to the old channels and sends

a HANDOVER FAILURE message. The MS proceeds on the old channels

Default: 0,675 seconds.

T8 Start: HANDOVER COMMAND message Stop: HANDOVER COMPLETE message from BTS to BSC or

HANDOVER FAILURE message from MS Expiry: BSC releases the old channels

The connection to the MS is lost Default: 5 seconds.

NY1 * T3105 Start: PHYSICAL INFORMATION message Stop: CORRECT FRAME from MS Expiry: BSC releases the new channels after receiving a CONNECTION

FAILURE message from the BTS with cause “Handover access failure“. The connection to the MS is lost, if no HOV failure message was received from MS

Default: NY1 = 20; T3105 = 0,080 seconds. Remark: T3124+ delta < NY1 * T3105 < T8 <= 10 sec


168


There are different scenarios for unsuccessful intra BSC handover: 3. Handover Command

MS is not able to get handover command message sent by the BSC, => Expiry of Timer T8, => BSC releases old and new channel(s). => Loss of MS connection,

4. Handover Access Target BTS is not able to get handover access message sent by the MS => Expiry of Timer T3124 => Handover failure message will be sent by the MS. => BSC releases new channel(s). => MS returns to the old channel(s).

5. Physical Info MS is not able to get physical info message sent by the BTS. Case 1: => Expiry of Timer T3124, => MS sends a handover failure message to the BSC. => BSC releases new channel(s). => MS returns to the old channel(s), Case 2: => Expiry of Timer NY1 * T3105, => BTS sends a connection failure message to the BSC. => BSC releases old and new channel(s). => Loss of MS connection

6. Correct frame MS got a physical info message, but the target BTS is not able to get correct frame from the MS. => Expiry of Timer NY1 * T3105 => BTS sends a connection failure message to the BSC. => BSC releases old and new channel(s). => Loss of MS connection.

7. Handover Complete MS is not able to get handover complete message sent by the MS, => Expiry of Timer T8 => BSC releases old and new channel(s). => Loss of MS connection,


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INTRA BSC HANDOVERMS BTS1 BSC1 BTS2 MSC

MEAS REP INTER CELLHO COND IND

(ATINHIRC, AALTCHTI,ATTCHSEI)

CHAN ACTIV(MTCHBUTI)

CHAN ACTIV ACKHO COMMAND

(AOUINHIR, AININIRH)

HO COMMANDHO ACCESS

HO ACCESSHO DETECTPHYS INFO

PHYS INFO

PHYS INFO

SABM

ESTABLISH INDUA

(TNTCHCL)

HO FAILUREHO COMPLETE

HO FAILURE(HOFITABS, UNINHOIE)

HO COMPLETE

HO PERFORMED

T3124

(SININIRH, SOUINIRH,SINHOBSC, SINTHINT)

T8 (UNIHIRLC)

NY1*T3105CONN FAILURE

(SUCTCHSE)

(NRFLTCH)

Fig. 67 Intercell handover, intra-BSC


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4.2.5.3 Inter-BSC Handover If during a connection the BTS notices from the values periodically transmitted by the MEASUREMENT REPORT messages, that the previously set threshold values for quality (RXQUAL), reception level (RXLEV), better cell or distance have been reached, the BTS decided to do a Handover. Therefore the BTS reports this to the BSC with a HANDOVER CONDITION INDICATION message. The BTS keeps a Target Cell List, which it uses as a basis to decide whether an inter-cell or an intra-cell handover is required. If the first cell on the list is in another BSC area, the BSC sends an HANDOVER REQUIRED message to the MSC. If the cell is one, which the BSC manages, it initiates an intra-BSC handover. In the case of an inter-BSC handover, the Target Cell List is contained in the HO REQUIRED message to the MSC. The MSC selects the first cell from the list and with an HANDOVER REQUEST message requests a channel for the handover from the new BSC. The BSC selects a suitable RR and activates it, with the message CHANNEL ACTIVATION. If the TCH is successfully activated, the BTS responds with a CHANNEL ACTIVATION ACKNOWLEDGE message. If the BSC can provide the requested resource, it replies to the MSC with a HANDOVER REQUEST ACKNOWLEDGE message. The MSC send a HANDOVER COMMAND message to the old BSC. The old BSC for its part forwards the HANDOVER COMMAND message, which contains information on the new mobile cell, to the mobile station (MS). With a HANDOVER ACCESS message, which can be repeated twice, the mobile station occupies the new channels it has been assigned in the target cell. If the new BTS receives the Handover Access message, it indicates the new BSC, that it can see the mobile station. The BSC forward this message further on to the MSC. The BTS synchronized on the new TRX and transmits a PHYSICAL INFORMATION message to the mobile station. The mobile station replies to the PHYSICAL INFORMATION message with a HANDOVER COMPLETE to the new BTS. The HANDOVER COMPLETE message is forwarded to the MSC. If Timer 3124 in the MS expires, before the MS receives a PHYSICAL INFORMATION message from the BTS, it reverts to the old channels and sends a HANDOVER FAILURE message over the old channels to the old BSC. The BSC informs the MSC about this failure by forwarding it to the MSC. The MSC then starts to clear the previously occupied channels in the new BSS with a clearing sequence.


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Other reasons for the failure of a handover may be for example:

the BSC assigns a new channel whose mode is not supported by the MS. The BSC assigns a new frequency to the MS, which the MS does not support.

The MSC then initiates the release of the old channels with a CLEAR COMMAND to the old BSC. “Synchronous“ or “pseudo-synchronous“ handovers, where the PHYS INFO message is not necessary, are not currently supported.

Timer In the Inter BSC Handover Procedure the Timer are used to supervise the channels. The BSS must keep the old channel as long until the MS has occupied the new one. The Mobile must have the possibility to go back to the old channel.

T3124 Start: HANDOVER ACCESS message. Stop: PHYSICAL INFORMATION message. Expiry: MS reverts to the old channels and sends

a HANDOVER FAILURE message. The MS proceeds on the old channels.

Default: 0,675 seconds.

T8 Start: HANDOVER COMMAND message. Stop: CLEAR COMMAND message from MSC or

HANDOVER FAILURE message from MS. Expiry: BSC releases the old channels.

The connection to the MS is lost. Default: 5 seconds.

NY1 * T3105 Start: PHYSICAL INFORMATION message. Stop: CORRECT FRAME from MS. Expiry: BSC releases the new channels after receiving a CONNECTION

FAILURE message from the BTS with cause “Handover access failure“. The connection to the MS is lost, if no HOV failure message was received from MS.

Default: NY1 = 20; T3105 = 0,080 seconds. Remark: T3124+ delta < NY1 * T3105 < T8 <= 10 sec


172


There are different scenarios for unsuccessful inter BSC handover: 1. Handover Command

MS is not able to get handover command message sent by the BSC, => Expiry of Timer T8, => MSC releases old and new channel(s). => Loss of MS connection,

2. Handover Access Target BTS is not able to get handover access message sent by the MS => Expiry of Timer T3124 => Handover failure message will be sent by the MS. => MSC releases new channel(s). => MS returns to the old channel(s).

3. Physical Info MS is not able to get physical info message sent by the BTS. Case 1: => Expiry of Timer T3124, => MS sends a handover failure message to the MSC. => MSC releases new channel(s). => MS returns to the old channel(s), Case 2: => Expiry of Timer NY1 * T3105, => BTS sends a connection failure message to the BSC. => MSC releases old and new channel(s). => Loss of MS connection

4. Correct frame MS got a physical info message, but the target BTS is not able to get correct frame from the MS. => Expiry of Timer NY1 * T3105 => BTS sends a connection failure message to the BSC resulting in a clear request message send to the MSC. => MSC releases old and new channel(s). => Loss of MS connection.

5. Handover Complete MS is not able to get handover complete message sent by the MS, => Expiry of Timer T8 => MSC releases old and new channel(s). => Loss of MS connection,


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INTER BSC HANDOVER

MS BTS1 BSC1 MSC BSC2 BTS2

MEAS REP INTER CELLHO COND IND

(ATINBHDO)

HO REQUIRED HO REQUEST CHAN ACTIVCHAN ACTIV

ACKHO REQUEST

ACKHO COMMANDHO COMMANDHO COMMANDHO ACCESSHO ACCESS

HO DETECT HO DETECTPHYS INFOPHYS INFO

SABM

ESTABLISH IND(TNTCHCL)

UA

HO COMPLETE

HO COMPLETE(SUCTCHSE)HO COMPLETECLEAR

COMMAND

(SUINBHDO)

T3124

T8

NY1*T3105

HO FAILUREHO FAILURE

(NRUNINHD)

(MTCHBUTI)

(ATTCHSEI,AALTCHTI)

CONN FAILURECONN FAILURE(NRFLTCH)

Fig. 68 Inter-BSC handover


174


4.2.5.4 Directed Retry A handover giving the reason "directed retry" is performed if no TCH is free in the cell after the call setup on the SDCCH. Using a FORCED HO REQUEST message the BSC then arranges for the BTS to send an INTERCELL HO COND IND message with a list of suitable neighbors for a handover (Target Cell List). The BSC selects a suitable cell from the list. If the cell is within its own BSC's area, the BSC uses it to occupy a TCH and sends an ASSIGNMENT COMPLETE message to the MSC. If the cell is within another BSC's area, the BSC sends an HO REQUIRED giving the reason "directed retry" to the MSC.

DIRECTED RETRYMS BTS1 BSC1 BTS2 MSC

MEAS REP

INTER CELL HO COND IND

(ATINHIRC, AALTCHTI, ATTCHSEI

CHAN ACTIV(MTCHBUTI)

CHAN ACTIV ACKHO COMMAND(AOUINHIR, AININIRH)

HO COMMANDHO ACCESSHO ACCESS

HO DETECTPHYS INFOPHYS INFO

SABM

ESTABLISH INDUA

(TNTCHCL)

HO FAILUREHO COMPLETE

HO FAILURE(HOFITABS, UNINHOIE)

HO COMPLETE

ASS COMPLETE

T3124

(SININIRH, SOUINIRH,SINHOBSC, SINTHINT)

T8 (UNIHIRLC)

NY1*T3105CONN FAILURE

(TASSUCC,SUCTCHSE)

(NRFLTCH)

ASS REQUEST(TASSATT, ATTCHSEI,ATCHSMBS)

FORCED HO REQ

Fig. 69 Directed retry


175

SSMC Training Center TEMS Investigation

5 TEMS Investigation


176

TEMS Investigation SSMC Training Center

The Test Mobile System TEMS can be used to initiate events and to monitor the air interface. TEMS consists of: A Test Mobile Station (MS1) A PC with the Test Mobile Software from Ericsson Erisoft AB Optional: A second Test Mobile Station (MS2) Optional: A positioning equipment Supported Test Mobile Stations (depending on which TEMS version is used): Ericsson GH 337, TMS300/1 Ericsson GH 388, TMS300/2 Ericsson GH 688, TMS300/3 Orbitel TMT-901, TMS200/2 Orbitel TMT-900, TMS200/1 PC hardware requirements: IBM compatible PC, minimum 80386 harddisk, minimum 4 Mb RAM, mouse at least 1 available serial port and serial cables to connect MS1(Voice)-PC, MS1(Data)-PC, MS2(Voice)-PC, MS2(Data)-PC, positioning equipment-PC PCMCIA card with two serial ports, if necessary Software requirements: DOS 5.0 or higher Windows 3.1 or higher Supported positioning equipment: GPS MAGNAVOX MX4200 (CDU) GPS MAGNAVOX MX4200 (RAW) GPS MOTOROLA PVT6 Trimble Placer GPS/DR (TAIP format) Trimble Mobile (PCMCIA) MAGNAVOX DRM (DeadReckoningModule) BOSCH Travel Pilot GPS equipment supporting NMEA-0183 Standard Power supply system in v


177


TEMS Investigation is an air interface test tool for real-time diagnostics. It lets you monitor voice channels as well as data transfer over GPRS. Data is presented in real time throughout. This makes TEMS Investigation ideal for advanced drive testing sessions of troubleshooting, performance tuning, etc. All data can also be saved in log files for purposes of post-processing. The diagram below is the interface of TEMS investigation.

Fig. 70 TEMS investigation information window

There are many functions in TEMS Investigation, here only most common used functions are introduced. For details, please refer to the user manual of TEMS Investigation.


178


5.1 Cells definition TEMS Investigation can present information about individual cells in the network. In particular, it is possible to present site locations on maps and to display cell names in plain text, simplifying their identification. Information on cells is provided in a cell definition table.


179


5.1.1 creating a cell definition table

To create a cell definition table, you have two ways Entering cell information in the Cell Definition window Open the Cell Definition window from the Navigator. For each cell a number of parameters must be specified. These are given in the column headers of the Cell Definition window. The cell definition table can be sorted by any column; click a column header to sort by the corresponding column. Step: 1 Edit cell name Select configuration in the main menu line Select Cell Definition in drop-down list

Double-click the Add Cell Name icon Input the values in the following session window

Fig. 71 Cell edit window

The latitude and longitude values are always presented in decimal minutes. When entering them, however, you can also use decimal degrees, or degrees, minutes and seconds. Step:2 Edit neighbor table Select the neighbors tab Click Apply if you want to add more cells. Click OK when you are finished adding cells.


180


All the entered cells are now listed in the Cell Definition window.

Fig. 72 neighbors table edit window

You can assemble your cell definition table manually by entering cell information directly in the Cell Definition window, adding one cell at a time. However, if you have a large number of cells, this is cumbersome. It is then more practical to use another way, which is


181


5.1.2 Creating a Cell Definition Table Outside TEMS Investigation

Since cell definition tables are saved as ASCII text files, you can manipulate them outside TEMS Investigation. A quick way to create a file with the correct format is to proceed as follows: Step: 1 Use the Cell Definition window to add one cell as described above. Save this file. Step: 2 Open the file with some program suitable for editing text files and add the remaining cells there. Note: Since the cell definition file has tab delimited data columns, a spreadsheet application can be used as editor. Save the file as tab-delimited plain text

Fig. 73 Cell definition table edited

Step: 3 Activating a Cell Definition Table To make a cell definition table active, it must be loaded in the General window. Select the Configuration in the main menu line Open the General window from the Navigator. Select the row "GSM" and right-click in the window to access the Properties dialog.


182


Fig. 74

Check "Use cell name" and browse to select your file. Once the cell definition file has been loaded, it immediately becomes active and governs how cells are presented in presentation windows. In particular, it enables showing cell site information in the Map window.


183


5.2 Connecting external equipment

5.2.1 Identify external equipment To identify external equipment such as TEMS, GPS, you have two ways, “Semi-Automatic” Enabling or “Manual” Enabling.

5.2.1.1 "Semi-Automatic" Enabling You can instruct TEMS Investigation to scan all COM ports in order to detect external devices. All devices found are then enabled automatically in the application.

Click the Identify Equipment button on the Equipment Control toolbar or in the Port Configuration window (in Configuration drop-down list). The detected external devices are listed in the Port Configuration window as they are identified (such a window is opened automatically if you used the button on the Equipment Control toolbar).

Fig. 75

The detected devices are automatically enabled, but not connected; this state is indicated by a red-light symbol to the left of each device. The same equipment symbols are also shown in the main window status bar. The Identify Equipment function is "semi-automatic" in the sense that it does not automatically detect new devices that are connected physically to ports. You must click the Identify Equipment button when you want to update the list of enabled devices.

5.2.1.2 "Manual" Enabling: Adding One Device at a Time External equipment can also be enabled one device at a time. If you use this method, you must indicate the type of the device (e.g. "R520m") yourself.


184


Click the Add button on the Equipment Control toolbar or in the Port Configuration window (in Configuration drop-down list).

Fig. 76

Select the correct COM port. Note that you must know the port number yourself (which might not be trivial with some kinds of peripherals).

Select the type of external device. For the R520m, choose "R520m" for the TEMS cable, and choose "R520m Data Cable" for the DATA cable. The two cables will be treated as different devices in TEMS Investigation. The TEMS cable will be appear as an "MS" device as usual, whereas the DATA cable will appear as a "DC" device.

The enabled device appears in the Port Configuration window.


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5.2.2 Connecting and Disconnecting External Equipment

Connecting of external devices is done as a separate step. You can however connect (and also disconnect) all devices at once. Note:Remember that the TEMS Investigation mobile must be attached before you can connect other devices. If you have a log files open, you must close it to be able to connect equipment To connect a single external device, choose it in the combo box of the Equipment Control toolbar, then

Click Connect on the Equipment Control toolbar. To connect all external devices,

Click Connect All on the Connections toolbar. Connected devices are accompanied by a green-light symbol in the combo box. The same symbol appears in the status bar and in the Port Configuration window.

5.2.2.1 Disconnecting External Equipment To disconnect a single external device, choose it in the toolbar combo box, then

Click Disconnect on the Equipment Control toolbar. To disconnect all external devices,

Click Disconnect All on the Connections toolbar. For a disconnected device, the symbol representing it reverts to red.


186


5.3 Logfiles

Click Start Recording on the Recording toolbar.

You are asked to name the logfile. The default naming format is MMDD_nn.log, where MM is the current month, DD is the current day of the month, and nn is an incrementing counter starting at 01.

To pause the recording without closing the logfile, click Pause Recording. Click the button once more to resume the recording. Special events indicating pausing and resumption are written to the logfile.

Click Stop Recording to end the recording and close the logfile. Once you have closed it, you cannot log any more data to the same file. Alternatively, you can control the recording with the corresponding commands in the Logfile menu.


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5.4 Presentation

The following presentation windows are available in TEMS Investigation status windows, which present information elements in tabular form message windows, which present messages or events in lists the GPS window the line chart the map

5.4.1 Status window and Message window The status windows present information elements in tabular form. There are a number of ready-make windows designed for presenting particular categories of information (such as signal strength or SQI). The information elements in the status window are pre-defined by TEMS Investigation. However when required, you can change status window properties Right-click in the status window and choose Properties from the popup menu. The mode tab governs the layout and appearance of the window:

Fig. 77


188


To edit the contents of the status window, select the cell content tab.

Fig. 78


189


Double –click on a row and select an information element from the list. Then click Edit.

Fig. 79

In a status window, you might want to show the same information element for several mobile stations. To do this, create new columns as needed on the Mode tab, and modify headers and insert information elements on the Cell Contents tab.

The message windows are used to list messages and reports received or transmitted by the mobile station such as layer 2 and layer 3 messages. In all message windows, you can double-click a message to open a window detailing the contents of the message. Also, all message windows allow installation of a filter specifying which types of message should be printed in the window during replay. This allows you to spot more easily the messages that are currently relevant to you. Right-click in the message window and choose Properties from the popup menu. The filter tab governs which messages are printed in the window during replay.


190


Fig. 80

Click “Filter…” button to select which message should be visible in the message window.

Fig. 81

To make a message type visible, select it and then click Add. To make all messages in a folder visible, select the folder and click Add. When you are finished adding messages, exit by clicking Done.


191


5.4.2 The Line Chart In the line chart you can plot numerical information elements in order to visualize how their values evolve over time. The line chart can also present events.

Fig. 82

It is sometimes useful to change line chart contents and properties. To edit the contents of the line chart and their presentation, right-click anywhere in the Line Chart window and choose Properties.


192


Adding Charts

Fig. 83

To add a new chart in the Line Chart window, click Add Chart. The Line Chart window can hold up to four charts.


193


Editing the Contents of a Chart Select the chart you want to edit in the list box. Click Edit Chart. A three-tab dialog appears:

Fig. 84

Information Elements Tab Here you edit the set of information elements to plot and how to present them. The information elements that can be plotted are chiefly those that represent or are derived from measured physical quantities (e.g. RxLev, C/A, SQI, TA). Flags, ARFCN numbers, timeslot indicators, and the like cannot be plotted. First select information element category in the System combo box. Using the arrow buttons, move the elements you want to present from the "Available IEs" to the "Selected IEs" list box. (A maximum of seven elements can be presented.) You can use Ctrl and Shift to select multiple items in the boxes. The first time you move an information element to "Selected IEs", it will be picked from the mobile the line chart is drawn for (see the title bar; for the Line Chart template it is MS1). From elements with an argument the value with the lowest argument is picked. If you move the same element to "Selected IEs" again, one of two things will happen: if the element has an argument, it is taken from the same mobile as before, and the value with the next higher argument is shown; otherwise, the element is taken from the next mobile.


194


Naturally, the MS and argument can also be edited directly at any time. This is done by clicking the Edit IE button. In the ensuing dialog you also customize the presentation of the information element: Events Tab Here you decide which events should appear in the line chart presentation. Using the arrow buttons, move the event you want to present to the "Selected IEs" list box. The first time you move an element to "Selected events", it will be picked from the mobile the line chart is drawn for (see the title bar). If you move the same element to "Selected events" again, it is taken from the next mobile. Clicking the Edit Event button pops up the following dialog:

Fig. 85

Additional Information Tab Here you choose the information elements to view in the Additional Information pane. This tab works exactly like the Information Elements tab, except that here any information element can be selected. Clicking the Edit IE button in this case naturally only offers editing of mobile and argument, since the additional information is presented only as text and not graphically. Deleting a Chart In the Line Chart Properties dialog, select the chart you want to delete and click the Delete Chart button.


195

SSMC Training Center K1205 Protocol Tester

6 K1205 Protocol Tester


196

K1205 Protocol Tester SSMC Training Center

6.1 Design of the K1205 Protocol Tester


197


The K1205 Protocol Tester analyzes wide area communication networks with CCS7, GSM 900, DCS 1800, PCS 1900 and CDMA protocols. There can be monitored up to 16 PCM interfaces and 32 signaling links simultaneously by using the K1205. The K1205 can capture the signaling channels and the framing automatically when monitoring PCM routes. E1/T1 interface boards for PCM routes are available so far. Using the approximately 150 implemented WAN communication protocols – including a number of national and manufacturer-specific variants – almost all signaling datas can be decoded and analyzed Online as well as Offline. The K1205 Protocol Tester is

designed in modular form: the modular design using the VME bus enables optimum adaptation to different tasks. The modular concept of the K1205 with four slots for the interface modules makes the K1205 extendable. convenient to operate: the individual measuring modules are simply put into K1205. The Windows NT 4.0 interface then guides you through operation. easy to transport: due to a total weight of approximately 10 kg and its compact design the K1205 can be transported to the site of use. A transport case is available for safe transport.


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K1205 Hardware: The K1205 Protocol Tester consists of a basic device and the individual measuring modules The basic device is equipped with:

a powerful Pentium PC board a hard disk of 2 GB and VME bus a TFT display (XGA) two PCMCIA card slots a 3.5’’ floppy disk drive and a removable keyboard with integrated trackball

The following interfaces are located on the cover of the PC module in slot 1:

socket for external PS/2 keyboard (KBD) serial interface (COM1) parallel interface (LPT1) 10-Base2 and 10-BaseT sockets for LAN connection socket for external monitor (VGA)

Furthermore, there are also an LED indicating the operating state of the Hard Disk (HD) . On the left hand side is a Reset Switch (RESET): The slots 2 to 5 are available for the Measuring Modules.


199


The Protocol Tester K1205 is designed for monitoring PCM links in a GSM network as following:

Interface Network components Abis BSC <---> BTS

A MSC/VLR <---> BSC

C/D MSC/VLR <---> HLR/AC

E/G MSC/VLR <---> MSC/VLR

MSC <---> PSTN


200


6.2 Basic Introduction for K1205 Protocol Tester Handling


201


This document is aimed to introducing people to the K1205. For more information refer to the “User Manual” (C73000-B6076-C91).

6.2.1 HW Set Up The device must be operated with 115 VAC or 230 VAC operating voltage only. The switchover 115/230 V is made automatically. The keyboard cable must be connected to the keyboard interface underneath the front cover below the display. The K1205 can be connected to the data line in the „on or off“ state to the measuring modules which are located underneath the device cover of the K1205. The interfaces on the E1/T1 boards are 9-pin Sub-D sockets. The cable length should be less than 3m. The individual measuring modules and the interfaces (sockets) can be controlled via the K1205 application.


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6.2.2 Power Up... Switch on the K1205 using the ON/OFF Switch on the right hand side of the device. The K1205 is set ready-to-run upon delivery, i.e. Windows NT is installed as operating system as well as the K1205 application. The device automatically boots after switching on. The operating system is loaded and the K1205 application is then started automatically. The Status Window shows status messages for the individual modules. If the modules boot without errors, the message “K1205 boot OK” will be displayed. The following dialog appears for loading the configuration (example):

Fig. 86


203


Click Autoconfiguration

Fig. 87

Confirm your selection with „Yes“ to configure the system automatically. The current configuration can be saved afterwards. After the autoconfiguration has been carried out, the active signaling channels are available.


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6.2.3 K1205 Application

The K1205 application is started with an initial screen which shows the version number of your K1205 application on top of the screen and information on the load state of the software is shown at the bottom. If you start the autoconfiguration, the autoconfiguration feature detects the signaling channels and the framing of the connected data lines automatically. The second possibility is to start an already created configuration. After the autoconfiguration has been carried out, the active signaling channels are available. There are two different tabs for setting parameters of interface modules, links and measurements:

Cards Overview and Measurement Scenarios.

The Cards Overview tab provides an overview of the connected interface modules. Here the setup settings of modules and ports can be defined, or already existing configuration settings changed. The left panel, „Tester Overview“, displays the interface modules, ports and the line configurations currently set. The right panel, Cards Overview, shows the individual sockets on the cards including module designation. By clicking the button „Configure Card“ the ports can be configured.


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Fig. 88 Cards Overview

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In the Measurement Scenarios tab of the Data Flow window, configure your measurement task by defining data sources and parameters for the measurement. The Measurement Scenarios tab keeps you informed about the currently active parameter settings and system status at all times. The gray boxes in the pipelines represent measurement modules (processing elements). The connection lines indicate the data flow between the modules. The left panel, List of Scenarios, displays the available measurement tasks (scenarios) as well as the currently configured measurement tasks and the outline sources. On the right hand side, the Measurement Scenarios Panel displays the pipelines as-signed to the measurement tasks. As soon as the K1205 application is started, the K1205 online help is available: Click Help in a K1205 application window using the trackball or mouse or press „F1“. The K1205 online help gives context-sensitive assistance.


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Fig. 89 Data Flow Window with Measurement Scenarios

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6.2.4 Starting Measurements

The autoconfiguration feature defines an online data source (Scenario) automatically and generates an online measurement scenario as a pipeline which contains several branches for individual measurement tasks. An online data source is a group of logical links. A logical link consists of a channel and a channel data interpretation rule. The settings for each data source, as detected by the autoconfiguration feature, are displayed in the expanded left part of the window under „List of Scenarios“ (to expand, click “+”): Up to eight logical links can exist for each data source. The following information is provided: [1]C:16:–:64 [Whibisup.stk] (example) 1: first board C: port MON C 16:–:64 timeslot 16, no subchannel (–), with 64 kbit/s Whibisup.stk detected protocol setting, here: the stack for SS#7 White Book

according to ITU-T

To load the actual protocol stack for GSM: Double click on „[1]C:16:–:64 [Whibisup.stk]“ (example) and select „Browse“ Go to the directory „gsm2“ and select either the file „gsm2_a.stk“ for an A-Interface trace or „gsm2_sabis“ for an Abis-Interface trace. Open the file and click on „ok“.

Take care that the selected channel is equal to the configured signaling channel. Use identical parameter values for logical links assigned to port A and B.


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Fig. 90

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The right side of the window (Measurement Scenarios) contains the online measurement scenario (a pipeline with the following branches: Recording, Monitor, and Statistics):

Fig. 91


212


To start online monitoring, click the ON/OFF Switch of the Monitor pipeline branch to ON. The pipeline of the activated data flow is now green: the measurement is running. To view the signaling data of the activated data flow switch to the Monitor Main Window by clicking the processing element „Monitor“ at the right end of the pipe-line.

Fig. 92


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6.2.5 Online Monitoring

The Monitor Main Window consists of three views (see each title bar), which display the data flow at different levels of complexity. The datas in each view are constantly updated. In Live Mode (indicated in the Main Window Title bar), you can read the data as it is measured. This mode is set by default when you switch to the Monitor Main Window. If you click on a view and scroll the contents using the arrow keys (up and down), the system automatically switches into Freeze Mode (indicated in the Main Window Title bar). The continuous display of new data frames is then suppressed. Click the „Live Mode“ button to return to live mode.


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Fig. 93

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The Short View provides an overview and lists the detected data packets row by row in summary form. You can choose which information is important for your own overview. Select Monitor: Column Setup: Short View. The column „2. Protocol“ shows the layer 2 protocol. The displayed protocol parameters depend on which protocol stacks are loaded. You can choose how detailed the information should be displayed. Select Monitor: Column Set up: Frame View. The Hex View displays the protocol parameters of a frame selected in Short View in hexadecimal. Recording and Reviewing Monitoring Data The signaling data of the active data flow can be recorded in a special file for subsequent evaluation and/or offline analysis. This recording feature can be used in con-junction with or as an alternative to online monitoring. Recording data The right side of the window (Measurement Scenarios) contains a pipeline branch with the processing element Recording File, which displays a file icon. „NONE“ signifies that no recording file has been created. Click the processing element „Recording File“ to create a recording file.


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Fig. 94

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The following dialog box appears: Click to the right of c:\k1205\rec\ in the File Name field and enter a name for the recording file. Storing all your recording files in c:\k1205\rec\ facilitates the search for individual files later on. Press Browse to locate an existing file. You do not need to enter the file extension “.rf5” for K1205 recording files when entering the file name. The program appends it automatically. The remaining settings (Open Mode and File Size) are optional. Click „Close“ the file after each opening of the switch to ensure that the file closes properly. Confirm your entries with „OK“. The name of the recording file appears in the processing element „Recording File“. To start recording, click the „ON/OFF Switch“ of the Recording pipeline branch to „ON“.


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Fig. 95

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The signaling data of the activated data flow are written to the recording file until the file is full or until you terminate the process. The data in the recording file can be read after the current measurement is complete. You can stop recording by clicking the „ON/OFF Switch“ of the Recording branch to „OFF“. In most cases, datas are recorded and reviewed at different times. It is possible to check the contents of the Recording File immediately after recording data.

Fig. 96


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Reviewing recorded data Recorded data can be reviewed offline, for e.g. when the K1205 is not connected to the network. Click the „Rec View“(Recording Viewer) button on the right side of the Data Flow Window. The recording viewer pipeline is created under Measurement Scenarios:

Fig. 97


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Click the processing element „Recording File“. The following dialog box appears: Click „Browse“ to locate your recording file. K1205 recording files end with “.rf5”. K1103 recording files end with “.rec”. A double-click automatically enters the file into the Recording File Processing element. You can also change the protocol stacks assigned to the logical links. Confirm your selection with „OK“.

Fig. 98


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6.3 Appendix


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E1/T1 Interface Boards Each E1/T1 interface board (PRIMO: primary rate monitoring) has four independent PCM (E1/T1) monitor interfaces and can receive 8 signaling links with HDLC data. The K1205 can be extended to monitor 16 PCM interfaces and 32 signaling links simultaneously. In addition a headphone connector with a mini jack on the E1/T1 interface board’s cover is provided for listening to audio data. Two transmission rates are supported: 1.544 MBit/s (T1) and 2.048 MBit/s (E1), with the following frame formats:


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T11,544 MBIT/S

F4AMI/B8ZS

F12 D3/D4AMI/B8ZS

ESF CRC6 ON/OFFAMI/B8ZS

F72AMI/B8ZS

T1

Receiver input: 0-36 dB75 ohms/100 ohms/high impedance (approx. 0,75 kOhms)

E12,048 MBIT/S

DOUBLEFRAMEHDB3

MULTIFRAME-CRC4HDB3

MULTIFRAME+CRC4HDB3

E1

Receiver input: 0-36 dB75 ohms/120 ohms/high impedance (approx. 0,75 kOhms)

Fig. 123


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