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Dimensioning Rules for Cs and Ps Traffic With Bss Software Release b9
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This document provides dimensioning rules of the A9120 (G2) BSC, A9135 MFS and A9130
BSC/MFS Evolution equipments with the BSS release B9.
When not explicitly mentioned otherwise,
• “BSC” will refer to both A9120 BSC and A9130 BSC Evolution;
• “MFS” will refer to both A9135 MFS and A9130 MFS Evolution
It also provides the rules to dimension the interfaces in the BSS Air interface, A-bis interface, A-ter
interface and Gb interface.
1 Product name may also be found with previous ALCATEL naming as A925 transcoder
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3. DEFINITIONS
A 64 kbit/s channel on the A-bis interface is called an A-bis timeslot.
A 16 kbit/s channel on the A-bis interface is called an A-bis nibble.
A transmission channel established for carrying (E)GPRS traffic is called a GCH (GPRS channel).
One GCH uses one A-bis and one A-ter nibble.
In this document, EDGE may be used instead of E-GPRS, for wording simplification purpose.
4. AIR INTERFACE
The maximum number of TRX per cell is 16.
Radio configuration of GSM cells :
There is one timeslot devoted to CCCH per cell.
The maximum number of SDCCH channels per cell is 88.These SDCCH channels may be static or
dynamic. At least one static SDCCH (SDCCH/4 or SDCCH/8) must be positioned on the BCCH TRX,
for recovery.
The maximum number of SDCCH per TRX on an EVOLIUM™ BTS is 24.
In a multiband cell, all SDCCH are in the primary band of the cell.
In a concentric cell, all SDCCH are in the outer zone.
All TRX can be declared as Full rate or Dual Rate TRX. Mixtures of DR TRX and FR TRX are
supported.
Packet configuration:
The maximum number of PDCH in one cell is 60.
There may be one primary master channel (PBCCH) and up to 3 secondary master channels
(PCCH) in one cell, all on BCCH TRX.
In a multiband cell, all packet traffic is in the primary band of the cell.
In a concentric cell, all packet traffic is in the outer zone.
In case of cell split over two BTS, packet traffic is supported over the master sector only.
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5. A-BIS INTERFACE
5.1 Number of time-slots available per A-bis Multidrop link
-
- This number depends on :
- The type of the multidrop link : Closed Loop or Open Chain,
- Whether time-slot zero (TS0) transparency1 is used or not,
- The BTS generation.
The table below indicates the number of time-slots available per PCM link according to the possible
choices:
OPEN CHAIN MULTIDROP CLOSED LOOP MULTIDROP
G1 or G2 BTS A9100 BTS (*) G1 BTS (**) G2 or
EVOLIUM™ BTS
WITH TS0 TRANSPARENCY 30 31 28 29
TS0 USAGE 31 31 30 30
(*) Improvement with EVOLIUM™ BTS: In case all BTSs of a Multidrop are EVOLIUM™ BTSs,
and if TS0 transparency is used, then the time-slot used for transmission supervision can be
saved (because the OML of EVOLIUM™ BTS supports also the transmission supervision
information)
(**) This column applies as soon as there is one G1 BTS in a closed multidrop.
5.2 Usage of A-bis timeslots
On the A-bis interface, there are basic timeslots, extra timeslots, and timeslots devoted to signalling.
One timeslot on the air interface is mapped on one basic 16kbit/s nibble on the A-bis interface.
As a consequence, each TRX corresponds to two A-bis basic timeslots. Additional extra timeslots
can be configured for the transport of packet. This makes sense when CS3/CS4 or EDGE has been
activated. If the cell transports voice only, or GPRS up to CS-2, there is no reason to add extra-
timeslots.
The number of extra timeslots per BTS is determined by the Operator. The granularity is one A-bis
timeslot.
For large BTS (up to 24 TRX or important packet traffic), two A-bis links may be used. The second A-
bis link transports voice, packet and signalling traffic.
1 Time slot 0 transparency means the BSS cannot use TS0, which is reserved by the transmission equipment for O&M purpose. Time Slot 0 Usage means the BSS can use TS0.
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5.3 Transport of Signaling on the A-bis interface
5.3.1 General
In addition to data, signalling has to be transported on the A-bis interface. There are two types of
information to be conveyed:
- RSL : Radio Signaling Link. There is one RSL per TRX
- OML : O&M link. There is one OML per BTS. The OML link is always on the first A-bis link.
When signalling multiplexing is not used, each signalling link (OML or RSL) is transported on a 64
kbit/s Abis channel. This configuration is however not recommended, as it is wasting bandwidth on
the Abis interface. The following section presents the various signalling multiplexing mode offered by
the ALCATEL BSS.
5.3.2 A-bis signaling multiplexing modes
There are three types of Signaling Multiplexing:
- Static Signaling Multiplexing consists of multiplexing on one A-bis time-slot (64 kbit/s) up to 4
RSLs (Radio Signaling Link) of 16 kbit/s each belonging to the same BTS. The OML uses an
additional A-bis time-slot (64 kbit/s).
- Statistical Signaling Multiplexing 64k consists of multiplexing on one A-bis time-slot (64 kbit/s)
up to 4 RSLs (Radio Signaling Link) of a BTS plus its OML. Each RSL and each OML has a
transfer rate of maximum 64 kbit/s (but not all simultaneously).
- Statistical Signaling Multiplexing 16k : the basic nibble corresponding to the radio timeslot 0 of
each TRX carries the RSL of this TRX and possibly the OML of the BTS. This feature requires
that no traffic, but only signaling (BCCH or SDCCH) is affected on timeslot 0 of each TRX. In this
case no additional timeslot is required on the A-bis for signaling.
5.3.3 Rules for usage of signaling multiplexing
5.3.3.1 Rules for Signaling Static multiplexing on 64 kbit/s channel
Static Signaling multiplexing can only be used if all the following conditions are met:
- - Full rate only (no Dual Rate).
- - Each TRX carries 8 SDCCH channels maximum
5.3.3.2 Rules for Signaling Statistical multiplexing on 16 kbit/s channel
Statistical Signaling multiplexing 16 k can only be used if all the following conditions are met:
- EVOLIUM™ BTS and Micro-BTS,
- Full rate only TRX (no Dual Rate).
- Each TRX carries 8 SDCCH channels maximum
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- The Time-Slot 0 of each TRX must not be assigned to traffic (but to BCCH/CCCH or SDCCH)
5.3.3.3 Rules for Signaling Statistical multiplexing on 64 kbit/s channel
- Statistical Signaling multiplexing 64 k can only be used on EVOLIUM™ BTS and Micro-BTS.
- The multiplexing ratio depends on the signaling load and on the configuration of the TRX (Dual
Rate or Full Rate).
- - It is not possible to mix the RSL of Full-Rate TRX and Dual-Rate TRX in the same 64 kbit/s
timeslot.
- Multiplexing ratio :
Full Rate TRX Dual rate TRX
Normal
signaling load
High signaling
load
Normal
signaling load
High signaling
load
4:1 2:1 2:1 1:1
- The signalling load is entered by the OMC-operator when choosing the multiplexing scheme. The
high signalling load is recommended in the case where several TRX in a cell are configured with
more than 8 SDCCH, which may be the case with multiband or concentric cells.
- In other cases the normal signalling load option should be advised.
5.4 Two A-bis links per BTS
Up to B8, a secondary A-bis link carried only extra A-bis timeslots for packet traffic.
In B9, the TWIN TRX gives the opportunity to put more TRX than 12 TRX inside a single BTS rack.
For this purpose, it is possible to configure a secondary A-bis link with basic A-bis nibbles in B9.
All topologies previously supported with the B8 feature “Two incoming A-bis links per BTS” are
supported (both Abis links may be mapped on a different TSUs for G2 BSC).
By default, the first A-bis link is filled up as much as possible.
Some additional flexibility is brought: It is possible to limit the number of TRX in the first A-bis link
(e.g. to optimise the filling of TSUs of a G2 BSC, when both links are connected to different TSUs).
Two parameters MAX_FR_TRE_PRIMARY and MAX_DR_TRE_PRIMARY define the maximum
number of TRX of a BTS, which are mapped on the first A-bis link (respectively for Full Rate and
Dual Rate).
Dual Rate TRX are mapped first, then Full Rate TRX, then Extra A-bis timeslots.
The OML of a BTS is always mapped on the first A-bis link.
The TCH and the RSL of a TRX are grouped on the same A-bis link.
All A-bis signalling modes are supported (with Statistical Signaling Submultiplexing 64 k, the multiplexing
mode “per sector” is not supported, i.e. the multiplexing mode is valid for the whole BTS).
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Some examples are described in Annex 2.
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6. BSC DIMENSIONNING RULES
6.1 BSC equipment overview
6.1.1 A9120 (G2) BSC
The G2 BSC range available with the BSS Software Release B9 is:
- In A9120 BSC rack, there is one sub-channel (on timeslot 14) on the first two A-ter
links (links N° 1, 2, 7, 8, 13 & 14) that is dedicated to the Qmux protocol. Three other
subchannels are used for TCH.
- In each A9130 BSC, there is one sub-channels (on timeslot 14) on the Ater links N°
1, 7, 13, 19, 25 and 2, 8, 14, 20, 26 that is dedicated to the Qmux protocol
(Transmission equipment supervision, two Qmux channels per cluster of 6 Ater link one
for redundancy). The three other sub-channels are used for TCH.
7.4 Minimum number of A-ter links
The minimum number of A-ter links connected to a BSS is 2.
7.5 Number of SS7 channels
The number of SS7 64 kbit/s channels required depends on the traffic mix.
There is a maximum of one SS7 64 kbit/s channel par A-ter link.
- With the Alcatel traffic mix presented in Annex 1, it is recommended to have one SS7 channel
per A-ter link.
For A9120 G2 BSC there is a maximum of 16 SS7 channels. This number of channels
is sufficient to cope with the signalling load corresponding to the G2 BSC maximum
committed capacity and BHCA from section 6.4.1.1, with the Alcatel traffic mix
presented in Annex 1, with a maximum 0,4 ERLANG per signalling channel.
For A9130 BSC-Evolution there is a maximum of 16 SS7 channels per BSC (so up to
32 in case of rack-sharing configurations, with 2 logical BSC). This number of channels
is sufficient to cope with the signalling load corresponding to the BSC evolution
maximum committed capacity and BHCA from section 6.4.1.2, with the Alcatel traffic
mix presented in Annex 1with maximum 0,6 ERLANG per signalling channel2.
2 As the ALCATEL BSC always balance the load on all signalling links in the BSC to MSC direction, in case of switch-over due to the loss of one signalling link, there is no risk of overloading SS7 in the transmit direction. In the receive direction, the possibility to allow more than 0,4 ERLANG per link set depends on the MSC strategy for load balancing in case of switchover (load balancing or N+1 redundancy or intermediate algorithm). It must also be noted that the traffic mix presented in Annex 1
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- With a different traffic mix than the one presented in Annex 1, the number of SS7 channels may
be adjusted so that the average SS7 load is about 0,4 ERLANG per channel. However, the
A9130 BSC-Evolution is able to cope with a signalling load up to 0,6 ERLANG per channel. The
MSC ability to cope with this load and the way used by the MSC to balance the traffic in the
MSC-to-BSC direction in case of loss of one link must however be checked before allowing 0,6
ERLANG per SS7 link.
7.6 Number of GSL channels
Each GPU or GP board requires at least one GSL channel.
There can be 0 or 1 GSL per A-ter link.
The required number of GSL channels depends on the traffic. The different parameters to calculate it
are given in document [10].
For security reason, it is recommended to have at least 2 GSL channels per GPU or GP board.
The maximum number of GSL per BSC is 24.
7.7 A-ter interface configuration rules
On the A-ter interface, from one up to 8 PCM can be connected to each GPU board (A9135 MFS),
and up to 13 PCM1 to each GP board (A9130 MFS). Each PCM link can be dedicated to packet
traffic or shared between CS and PS traffic.
For security reasons, the time-slots assigned to PS traffic should be spread among different A-ter
PCMs. However, when there is enough PS traffic to fill 2 or more PCMs, there is an advantage to
dedicate complete PCMs to PS rather than mixing PS with CS traffic. Indeed, doing so avoids
connecting the A9135 MFS to the Transcoder, with A-ter PCMs not fully devoted to circuit-switched
traffic, and thus avoids wasting transcoder resource.
It is possible to set PS time-slots on all A-ter PCMs; indeed, this can be useful in the case of
configurations with only 2 A-ter PCMs in order to ensure better security.
However, it is recommended not to carry PS traffic on the first A-ter PCM so that it can be connected
directly to the transcoder in order to enable MFS installation without O&M interruption on the BSC.
corresponds to a very high signalling load per user, and that in most cases the average signalling load per user is such that 0,4 ERLANG per signalling link is not reached with the highest capacity. 1 Reaching 13 Ater links per GP is possible only for MFS configurations allowing more than 13 links per GP ( max 13 Ater + 3Gb. See section 9.3, on page 24 for details on MFS and GP capacity.
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8. TRANSCODER DIMENSIONING RULES
8.1 Connection to the EVOLIUM™ G2 TC
Each BSC rack must be connected to only one TC G2 rack. But one TC rack can be connected to
several BSC racks.
(Please refer to the EVOLIUM™ G2 TC product description [6] for more details.)
8.2 Connection to the A9125 TC
It is possible to connect up to 24 BSCs on one A9125 Compact TC.
At least 2 A-ter links per BSC are required.
It is also possible to connect one BSC to different TC racks.
(Please refer to the A9125 TC product description [7] for more details.)
8.3 Minimum number of A links
The minimum number of A-ter links connected to a BSS is 2.
- - If the O&M link to the OMC-R is not conveyed by the A-ter interface, each A-ter link needs to be
connected to a minimum of one A interface link (total 2 A links).
- - If the O&M link to the OMC-R is conveyed by the A-ter interface, each A-ter link needs to be
connected to 2 A interface links (total 4 A links).
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9. MFS DIMENSIONING RULES
9.1 A9135 MFS configurations
The A9135 MFS can accommodate from 1 to 2 telecommunication sub-racks.
One GPU board per sub-rack is always dedicated to the n+1 redundancy feature.
Each GPU board is connected to only one BSC.
But one BSC can be connected to several GPU (up to 6 from B7 Release onwards), depending on
packet traffic. These GPUs can belong to different MFS subracks.
All the BSCs connected to a given MFS must be connected to the same OMC-R as the MFS.
There can be more than one A9135 MFS per MSC, and one A9135 MFS can be connected to BSCs,
themselves connected to different MSCs.
One MFS can be connected to several SGSN units. One GPU is connected to only one SGSN.
One A9135 MFS can control up to 22 BSCs.
One MFS can manage up to 2000 cells.
The maximum number of cell adjacencies handled by the MFS is 40000.
Both maximum (cells and adjacencies) may be reached with one sub-rack, but in this case they
cannot be increased when adding a second sub-rack.
9.1.1 MFS based on DS10 systems :
From the B8 release onwards, the MFS based on DS10 systems can house up to 32 GPU boards.
Hence each A9135 MFS sub-rack can include up to 15 GPU boards plus 1 GPU board for
redundancy. The granularity is 1 GPU board.
9.1.2 MFS based on AS800 systems :
The MFS based on AS800 systems can house up to 24 GPU boards.
Hence each A9135 MFS sub-rack can include up to 11 GPU boards plus 1 GPU board for
redundancy. The granularity is 1 GPU board.
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9.2 A9130 MFS configurations
The A9130 MFS Evolution can accommodate from 1 to 2 telecommunication sub-racks. Each A9130
MFS Evolution racks can include up to 21 GP boards plus 1 GP board for redundancy without any
subrack constraints.
Each GP board is connected to only one BSC. But one BSC can be connected to several GP,
depending on packet traffic (These GPs can belong to different MFS subracks).
One A9130 MFS Evolution can control up to 21 BSCs.
All the BSCs connected to the different GPs of a same MFS must be connected to the same OMC-R
as the MFS.
There can be more than one A9130 MFS Evolution per MSC, and one A9130 MFS Evolution can be
connected to BSCs of several MSCs.
One A9130 MFS Evolution can manage up to 3000 cells.
The maximum number of cell adjacencies handled by the A9130 MFS Evolution is 60000.
Both maximum (cells and adjacencies) may be reached with one sub-rack, but in this case they
cannot be increased when adding a second sub-rack
The maximum number of external links per A9130 MFS is 256.
9.3 GP/ GPU capacity
- A9135 MFS: One GPU board can support up to 16 external links (A-ter + Gb).
- A9130 MFS: One GP board can support:
- up to 16 external links (A-ter + Gb), with a maximum of 16 GP board per MFS.
- When the number of GP boards in the MFS is more than 16, the number of external
links per GP is limited, so that the total number of links per MFS is not exceeded (12 per
Note: For the GP board; the maximum number of PDCH is indicated for the configuration with 16
links per GP.
10. GB INTERFACE
The maximum number of links from one GPU or GP board to the SGSN is 8.
10.1 Configuration rules
There are 2 ways to connect the MFS and the SGSN via the Gb interface:
- Through the Transcoder and the MSC.
- Bypassing the Transcoder and going either directly to the SGSN (through the MSC or not). This
is the recommended solution when the traffic is sufficient to justify A-ter PCMs completely
devoted to GPRS traffic. However, depending on the hardware and software versions, this is
not always possible, because of the GPU synchronisation issues1.
The links between the MFS and the SGSN or between the MSC and the SGSN can be direct point-
to-point physical connections or an intermediate Frame Relay Network can be used..
1 For synchronisation issues, please refer to the A9135 MFS product description [4].
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The figure below displays the different types of links between the MFS and the SGSN.
BTS
BTS
BTS
BSC
MFS
TC
SGSN
MSC FRDN
A bis A ter A ter A
FrameRelayDataNetwork
BTS
BTS
BTS
BSC
MFS
TC
SGSN
MSC FRDN
A bis A ter A ter A
FrameRelayDataNetwork
Remarks:
- The links going through the MSC can benefit from the multiplexing capability of the MSC in order
to reduce the number of ports required to the frame relay network towards the SGSN.
10.2 General dimensioning rules
The peak throughput of the Gb interface is equal to the peak LLC throughput multiplied by an
overhead factor which takes into account the Gb interface overheads.
- -This overhead factor depends on the mean frame size.
- The maximum number of Frame Relay bearer channels is 120 per GPU board (theoretical
value). It is however interesting to reduce the number of bearer channels to 2 (for redundancy
reason) in order to take benefit from the statistical effect of using larger bearer channels.
For more information on the method to determine the Gb peak throughput according to the traffic mix
expected within the BSC area and the Gb interface overheads, please refer to [10].
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11. ANNEX 1: STANDARD TRAFFIC MODEL
For comparison reasons, the following models are standardized with: BHCA = MOC + MTC = 1
BHCA : Busy Hour Call Attempt
MOC : Mobile Originating Call
MTC : Mobile Terminating Call
Mean holding time (s)
Events Average ratio per
Call Attempt
SDCCH TCH SCCP
MO Call 0,6 4s 50s 54s
MT Call 0,4 4s 50s 54s
Internal Handover 2 - -
External Handover 1 - 4s
Location Update 3 3s 3s
IMSI Attach 0.5 3s 3s
IMSI Detach 0.5 3s 3s
Originating SMS
(PtP)
0.3 3s 3s
Terminating SMS
(PtP)
0.7 3s 3s
Paging (as occurred
in the A interface )
G2-BSC: 70
Paging/s
Paging (as occurred
in the A- interface)
BSC-Ev: 95
Paging/s
(*) In rack-sharing configuration, the maximum paging rate corresponds to the rate for two logical
BSC.
- The BSC can handle different call mixes. If a Customer’s traffic mix is significantly different from
the above Standard Traffic Model, Alcatel is prepared to study the possibility for the BSC to cope
with it.
- Performances versus traffic mix are committed upon BSC load test completion.
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12. ANNEX 2: A-BIS INTERFACE CONFIGURATION
12.1 Number of time-slots required with the different Signaling Multiplexing schemes
The table below gives the number of 64 kbit/s time-slots required with the different Signaling
Multiplexing schemes. The BTS is assumed to have n TRXs in total all working in Full-Rate mode,
and we shall use the notation “roundup(x)” when a value x is to be rounded up to the next higher
integer. For G2 sectored BTS, we shall note i, j and k the number of TRXs in sector 1,2,and 3.
Without
Signaling Multiplexing
Static-Signaling Multiplexing
Statistical- Signaling Multiplexing-64k
Statistical-Signaling Multiplexing-16k
Trafic (n TRX) 2n (2 per TRX) 2n (2 per TRX) 2n (2 per TRX) 2n (2 per TRX) OML if EVOLIUM™ BTS 1 per BTS 1 per BTS 0 0 OML if non EVOLIUM™ BTS (previous generation)
1 per Sector 1 per Sector Not applicable Not applicable
RSL if EVOLIUM™ BTS 1 per TRX Roundup (n/4) Roundup ( n/4) or Roundup(n/2) (*)
0
RSL if non EVOLIUM™ BTS ( G2-BTS)
1 per TRX Roundup(i/4)+ Roundup(j/4)+ Roundup(k/4)
Not applicable Not applicable
Number of A-bis time-slots required according to the different Signaling Multiplexing schemes
(*) Depends on signalling load: 4 for normal signalling load, 2 for high signalling load.
12.2 Typical cases where Signaling Multiplexing is very advantageous
- With Static Multiplexing, a sectored site with 3 x G2 BTS having 4 TRXs requires:
3x[ 1+ 4x2+ roundup ( 4 / 4 )] = 30 time-slots . Hence, it is possible to connect this site
with only one A-bis PCM (except if Closed Loop with TS0 transparency)
- With Statistical Multiplexing 64k, one EVOLIUM™ A9100 BTS having 3x4 TRXs requires