Wireless technologies - Part 1

04/08/23 Tinniam V Ganesh 1

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04/08/23 1

Tinniam.V.Ganesh

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Agenda – Session 1

1. Telecom and Wireless basics2. History of Telecom3. Digital Switching4. Anatomy of Telephone call5. PCM, Sampling, Nyquist criteria6. Multiplexing7. Principles of digital switching, time slot interchange8. Signaling events, ISUP Call flow9. Recap10. SS7 Protocol Stack11. SS7 Layers12. Wireless Technology Terminologies13. Recap14. Quiz

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Trends in Telecom

Technology Realization Period

Strowger, Crossbar exchanges

Electromechanical relays. Operator intervention

~1877 - 1975

Digital Switches

Time slot interchange. Entirely digital

~1965 onwards

Softswitch Separation of control and bearer signaling. IP as transport mechanism

~1996 onwards

IMS SIP, SDP signaling. All IP Core.

~ 2000 onwards

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Samuel Morse invents telegraph in 1837.

Alexander Graham Bell invents telephone in 1874.

Marconi experiments with wireless telegraph

Historical beginnings of Telecom…

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The initial exchanges were electro mechanical viz. Strowger and Cross bar exchangeLater the exchanges became entirely digital and were known as Electronic Switching System (ESS)

Early switching exchanges

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Mouth piece converts audio signal to electrical signal

Electrical signal transmitted over twisted pair

Electrical signal converted to vibrations in earpiece

Information transmitted as electrical signals

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• Digital Switches

• Sample voice signal• Digitize voice samples• Convert to Pulse Code Modulation• Multiplex at sending end and de-multiplex at receiving end• Perform Time slot switching or Time Slot Interchange

Digital Switches

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Voice is transmitted using Pulse Code Modulation.

At the sending the voice signal is sampled, and modulated before transmission

At the receiving end the signal is demodulated to obtain the original signal

Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a numeric (usually binary) code.

Pulse Code Modulation

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Audible speech is in the range of 300 Hz to 4 KHz.

Bandwidth of human voice

Sampling is the reduction of a continuous signal to a discrete signal

Quantization is the process of approximating a continuous range of values (or a very large set of possible discrete values) by a relatively small set of discrete symbols or integer values.

Sampling & quantization

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Nyquist sampling frequency

Nyquist sampling frequency requires that in order to faithfully reproduce a signal at the receiving end the sampling frequency should be twice that of highest frequency

Voice bandwidth is 300 Hz – 4 KHz.

Hence the sampling frequency should be 8 KHz.

Sampling a sine wave

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Calculations in PCM

8 bits per PCM sample and sampled at 8 KHz

8 bits * 8000 samples per sec = 64000 bits/s = 64 Kbps

This is also known as DS0 or E0

Digitizing sampled levels

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G. 711

G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972.

G.711 represents logarithmic pulse-code modulation (PCM) samples for signals of voice frequencies, sampled at the rate of 8000 samples/second.

A – law and µ - Law The µ-law and A-law algorithms encode 14-bit and 13-bit signed linear PCM samples (respectively) to logarithmic 8-bit samples. Thus, the G.711 encoder will create a 64 kbit/s bitstream for a signal sampled at 8 kHz.

There are two main compression algorithms defined in the standard, the µ-law algorithm (used in North America & Japan) and A-law algorithm (used in Europe and the rest of the world).

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Multiplexing

In telecommunications , multiplexing, is used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. For example, in telecommunications, several phone calls may be transferred using one wire.

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In Time-Division Multiplexing (TDM) two or more signals or bit streams are transferred simultaneously as sub-channels in one communication channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc.

Ch 2Ch 1 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8

Time

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Time-Division Multiplexing

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Standards in PCM transmission

There are 2 main standards in the world for transmission of PCM signals

T-Carrier – This is used in the North American marketE-Carrier – This is used for European market

T1 – 24 channels * 64 Kbps = 1.544 Mbps

E1 – 32 channels * 64 Kbps = 2.048 Mbps

Level North American European

0 64 Kbps 64 kbps

1 1.544 Mbps (T1) 2.048 Mbps (E1)

2 6.312 Mbps (T2) 8.448 (E2)

3 44.736 Mbps (T3) 34.368 (E3)

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Digital switches Digital switches aka as Electronic switches receive digitized voice samples. Voice is sampled and digitized Digitized PCM voice samples come to the digital switchSwitching or connecting callee and called party happens in memory by switching the voice samples in two different time slotsSwitching happens through a Time-Space-Time switching fabric

TDM

TDM

Time Slot

Inter-change

Signaling&

Control

Line Interfaces

Line Interfaces

Architecture of a traditional circuit switch

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i

k

Connection memory

5

7

k

i

Data out

i

k

Time slot counter

Data in

Speech memory

Write Address

Read Address

5 7 7 5Time Slot Interchange

i

k

i

k

Circuit Switching - Time Slot Interchange Functionality

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Signaling events in Telecom network

1. Off-hook or origination2. Dialing3. Ringing and Ring Back Tone (RBT)4. Answer5. Disconnection

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Terminations at a Digital switch

Digital switches connect the following terminations

1.Normal landlines or lines. 2.Trunk Lines (E1,E2,T1,T2 etc)

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Classes of Telecom switches 1. Class 5 switch – This switch has both lines and trunks. This

switch also supports features like call forwarding, call hold etc

Class 5 switch

1. Class 4 switch – This switch only supports trunks. This is also known as a Transit switch

Class 4 switchClass 5 switch Class 5 switch

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ISUP Call Flow

Switch A Switch B

A dials digitsInitial Address Message (IAM) B’s phone rings..

Address Complete Message (ACM)

B Answers

Answer Message (ANM)

A disconnects

Release Message (REL)

Release Complete (RLC)

B disconnects

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Wireless Networks

Wireless networks support wireless telephone calls using cell phones.The digital switch in a wireless network is called a MSC.

The network elements in a wireless network are1.MSC – Mobile Switching Center. This network element is switches the wireless calls between the calling and called mobile telephone2.HLR – Home Location Register - This is a database and stores the feature supported by each mobile phone viz. IMEI number, IMSI, features subscribed by the subscriber3.BTS – Base Transceiver Station. This network element keeps track of the location of mobiles and the forwards the digitized voice to the MSC4.BSC – Controls several BTS5.SCP – Service Control Point – Supports Intelligent Network6.VLR – Visitor Location Network – Keeps tracks mobiles roaming in its network

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Mobile Switching Centre (MSC)

HLR SCP

Other

MSC

VLR

Wireless Network

BSC

BTS

BTS

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Benefits of the circuit switches

Digital Switches have the following merits Are very feature rich. Lucent’s 5ESS has close to 3000 features Support 99.9999 % (6 nine’s) availabilitySupport all regulatory services like 911, CALEA etc

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SIGNALING SYSTEM 7 (SS7)

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WHAT IS COMMUNICATION ?• Communication is used between 2 network elements to exchange

information.• There are 2 types of domains in the communication world

Data communication Telecommunication

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DIFFERENCES BETWEEN TELECOM & DATACOM

Telecommunication Data Communication

Network used for making voice calls between telephones

Network used for transferring data from one computer to another

Telephones were the end points Computers were the end point

Uses protocols like ISUP, ISDN Predominantly uses TCP/IP

Network elements are MSC, HLR, SCP etc

Network elements are Routers, hubs, ATMs, bridges etc

Uses circuit switching Uses packet switching

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NETWORKS OF TODAY …• In the networks of today telecommunication networks are used to download data

e.g.GPRS

• Data networks are used for making Voice Calls e.g. VOIP

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WHAT IS SIGNALING ?• Signaling refers to the exchange of information between network elements• Signaling between network elements follows a specific protocol• A Protocol refers to the set of rules for communicating between the

elements

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WHAT IS SS7 SIGNALING ? Signaling System 7 was devised by ITU-T (formerly known as CCITT) Initially the signaling in trunks used to happen on the same channel in

which the voice call used to occur. Hence call setup, digits etc would use the same line as the actual voice circuit

In SS7 a separate channel is allocated just for signaling. This is known as Out-Of- Band signaling

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SS7 SIGNALING• Signaling happens in a separate channel outside of the voice channels• A separate timeslot is used to transfer signaling messages like call setup,

teardown etc• This is also known as Common Channel Signaling (CCS)

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ADVANTAGES OF OUT OF BAND SIGNALING

• Allows signaling at any phase of the call• Allows upto 56 Kbps of signaling information

Switch A Switch B

Voice Trunk

Signaling Link

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SS7 STACK

MTP 1

MTP 2

MTP 3

SCCP

TCAP

ISUP,TUP..

CAP,MAP…

Physical layer

Data link layer

Network layer

Network layer

Application layer

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SS7 LAYERS• MTP – Message Transfer Part• SCCP – Signaling and Connection Control Part• TCAP – Transaction Capabilities Application Part• CAP – CAMEL Application Part• ISUP – ISDN User Part• MAP – Mobile Application Part

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SS7 PROTOCOLSSS7 protocols can be classified as call related and non-call related

• Call related protocols – ISUP (ISDN User Part), B-ISUP (Broadband – ISUP)

• Non-call related protocols – – INAP (Intelligent Network Application Part)– CAP (CAMEL Application Part)– MAP (Mobile Application Part)– …

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SS7 STANDARD BODIES• The SS7 standard body for North American market is ANSI (American National

Standards Institute). The ANSI versions are ANSI ISUP, ANSI TCAP etc.

• The SS7 standard body for European market is ETSI (formerly CCITT). The ETSI versions of the protocols are ETSI ISUP, ETSI TCAP etc.

• There are minor variations in the protocols by the two standard bodies.

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SS7 Link speeds

There are 2 main standards in the world for transmission of PCM signals

T-Carrier – This is used in the North American marketE-Carrier – This is used for European market

T1 – 24 channels * 64 Kbps = 1.544 Mbps

E1 – 32 channels * 64 Kbps = 2.048 Mbps

Level North American European

0 64 Kbps 64 kbps

1 1.544 Mbps (T1) 2.048 Mbps (E1)

2 6.312 Mbps (T2) 8.448 (E2)

3 44.736 Mbps (T3) 34.368 (E3)

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SS7• Signaling System Number 7 (SS#7 or C7) is the protocol used by the

telephone companies for interoffice signaling. In the past, in-band signaling techniques were used on interoffice trunks. This method of signaling used the same physical path for both the call-control signaling and the actual connected call. This method of signaling is inefficient and is rapidly being replaced by out-of-band or common-channel signaling techniques.

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SS7 Stack

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SS7 Layers

Physical Layer (MTP-1)• This defines the physical and electrical characteristics of the signaling links of the

SS7 network. Signaling links utilize DS–0 channels and carry raw signaling data at a rate of 56 kbps or 64 kbps (56 kbps is the more common implementation).

Message Transfer Part—Level 2 (MTP-2)• The level 2 portion of the message transfer part (MTP Level 2) provides link-layer

functionality. It ensures that the two end points of a signaling link can reliably exchange signaling messages. It incorporates such capabilities as error checking, flow control, and sequence checking.

Message Transfer Part—Level 3 (MTP-3)• The level 3 portion of the message transfer part (MTP Level 3) extends the

functionality provided by MTP level 2 to provide network layer functionality. It ensures that messages can be delivered between signaling points across the SS7 network regardless of whether they are directly connected. It includes such capabilities as node addressing, routing, alternate routing, and congestion control.

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SS7 Layers (contd.)

Signaling Connection Control Part (SCCP)• The signaling connection control part (SCCP) provides two major functions that are

lacking in the MTP. The first of these is the capability to address applications within a signaling point. The MTP can only receive and deliver messages from a node as a whole; it does not deal with software applications within a node.

• While MTP network-management messages and basic call-setup messages are addressed to a node as a whole, other messages are used by separate applications (referred to as subsystems) within a node. Examples of subsystems are 800 call processing, calling-card processing, advanced intelligent network (AIN), and custom local-area signaling services (CLASS) services (e.g., repeat dialing and call return). The SCCP allows these subsystems to be addressed explicitly.

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SCCP

• The second function provided by the SCCP is Global Title translation, the ability to perform incremental routing using a capability called global title translation (GTT). GTT frees originating signaling points from the burden of having to know every potential destination to which they might have to route a message. A switch can originate a query, for example, and address it to an STP along with a request for GTT. The receiving STP can then examine a portion of the message, make a determination as to where the message should be routed, and then route it.

• For example, calling-card queries (used to verify that a call can be properly billed to a calling card) must be routed to an SCP designated by the company that issued the calling card. Rather than maintaining a nationwide database of where such queries should be routed (based on the calling-card number), switches generate queries addressed to their local STPs, which, using GTT, select the correct destination to which the message should be routed. Note that there is no magic here; STPs must maintain a database that enables them to determine where a query should be routed. GTT effectively centralizes the problem and places it in a node (the STP) that has been designed to perform this function.

• In performing GTT, an STP does not need to know the exact final destination of a message. It can, instead, perform intermediate GTT, in which it uses its tables to find another STP further along the route to the destination. That STP, in turn, can perform final GTT, routing the message to its actual destination.

• Intermediate GTT minimizes the need for STPs to maintain extensive information about nodes that are far removed from them. GTT also is used at the STP to share load among mated SCPs in both normal and failure scenarios. In these instances, when messages arrive at an STP for final GTT and routing to a database, the STP can select from among available redundant SCPs. It can select an SCP on either a priority basis (referred to as primary backup) or so as to equalize the load across all available SCPs (referred to as load sharing).

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ISUPISDN User Part (ISUP)• ISUP user part defines the messages and protocol used in the establishment and tear

down of voice and data calls over the public switched network (PSN), and to manage the trunk network on which they rely. Despite its name, ISUP is used for both ISDN and non–ISDN calls. In the North American version of SS7, ISUP messages rely exclusively on MTP to transport messages between concerned nodes.

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SS7 Layers (contd.)

Transaction Capabilities Application Part (TCAP)• TCAP defines the messages and protocol used to communicate between applications

(deployed as subsystems) in nodes. It is used for database services such as calling card, 800, and AIN as well as switch-to-switch services including repeat dialing and call return. Because TCAP messages must be delivered to individual applications within the nodes they address, they use the SCCP for transport.

Operations, Maintenance, and Administration Part (OMAP)• OMAP defines messages and protocol designed to assist administrators of the SS7

network. To date, the most fully developed and deployed of these capabilities are procedures for validating network routing tables and for diagnosing link troubles. OMAP includes messages that use both the MTP and SCCP for routing.

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SS7 Layers (contd.)

Mobile Application Part (MAP) messages sent between mobile switches and databases to support user authentication, equipment identification, and roaming are carried by TCAP. In mobile networks (IS-41 and GSM) when a mobile subscriber roams into a new mobile switching center (MSC) area, the integrated visitor location register requests service profile information from the subscriber's home location register (HLR) using MAP (mobile application part) information carried within TCAP messages.

• The Mobile Application Part (MAP), one of protocols in the SS7 suite, allows for the implementation of mobile network (GSM) signaling infrastructure. The premise behind MAP is to connect the distributed switching elements, called mobile switching centers (MSCs) with a master database called the Home Location Register (HLR). The HLR dynamically stores the current location and profile of a mobile network subscriber. The HLR is consulted during the processing of an incoming call. Conversely, the HLR is updated as the subscriber moves about the network and is thus serviced by different switches within the network.

• MAP has been evolving as wireless networks grow, from supporting strictly voice, to supporting packet data services as well. The fact that MAP is used to connect NexGen elements such as the Gateway GPRS Support node (GGSN) and Serving Gateway Support Node (SGSN) is a testament to the sound design of the GSM signaling system.

• MAP has several basic functions:• Mechanism for a Gateway-MSC (GMSC) to obtain a routing number for an incoming

call• Mechanism for an MSC via integrated Visitor Location Register (VLR) to update

subscriber status and routing number.• Subscriber CAMEL trigger data to switching elements via the VLR• Subscriber supplementary service profile and data to switching elements via the VLR.

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ISUP

• ISUP (ISDN User Part) defines the messages and protocol used in the establishment and tear down of voice and data calls over the public switched telephone network (PSTN), and to manage the trunk network on which they rely. Despite its name, ISUP is used for both ISDN and non–ISDN calls. In the North American version of SS7, ISUP messages rely exclusively on MTP to transport messages between concerned nodes.

• ISUP controls the circuits used to carry either voice or data traffic. In addition, the state of circuits can be verified and managed using ISUP. The management of the circuit infrastructure can occur both at the individual circuit level and for groups of circuits.

• Services that can be defined using ISUP include: Switching, Voice mail, Internet offload. ISUP is ideal for applications such as switching and voice mail in which calls are routed between endpoints.

• When used in conjunction with TCAP and SIGTRAN, ISUP becomes an enabler for Internet offload solutions in which Internet sessions of relatively long duration can be isolated from relatively brief phone conversations.

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The IMSI (International Mobile Subscriber Identity) is a unique 15-digit code used to identify an individual user on a GSM network.

The IMSI consists of three components:a) Mobile Country Code (MCC)b) Mobile Network Code (MNC)c) Mobile Subscriber Identity Number (MSIN)d) The IMSI is stored in the Subscriber Identity Module (SIM).e) It is also used for acquiring other details of the mobile in the Home Location

Register (HLR) or as locally copied in the Visitor Location Register. f) The IMSI is used in any mobile network that interconnects with other networks, in

particular CDMA and EVDO networks as well as GSM networks. This number is provisioned in the phone directly

IMSI - 310150123456789

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MCC 310 USA

MNC 150 AT&T

MSIN 123456789 MSIN

IMSI


TMSITMSI –Temporary Mobile Subscriber Identity

• A TMSI is used to protect the true identity (IMSI) of a subscriber. It is issued by and stored within a VLR (not in the HLR) when an IMSI attach takes place or a Location Area (LA) update takes place. At the MS it is stored in the MS’s SIM. The issued TMSI only has validity within a specific LA.

• Since TMSI has local significance, the structure may be chosen by the administration. It should not be more than four octets.

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MSISDN

MSISDN

• MSISDN is a number uniquely identifying a subscription in a GSM or a UMTS mobile network. Simply put, it is the telephone number of the SIM card in a mobile/cellular phone. This abbreviation has several interpretations, the most common one being "Mobile Subscriber Integrated Services Digital Network Number".

• The MSISDN together with IMSI are two important numbers used for identifying a mobile subscriber. The latter identifies the SIM, i.e. the card inserted in to the mobile phone, while the former is used for routing calls to the subscriber.

• The MSISDN represents the ‘true’ or ‘dialled’ number associated with the subscriber. It is assigned to the subscriber by the network operator at registration and is stored in the SIM.

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IMEI

IMEI• The International Mobile Equipment Identity or IMEI is a number, usually unique,to

identify GSM, WCDMA, and mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone. It can also be displayed on the screen of the phone by entering *#06# into the keypad on most phones.

• The IMEI number is used by the GSM network to identify valid devices and therefore can be used for stopping a stolen phone from accessing the network in that country. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "ban" the phone using its IMEI number

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MSRNMSRN – Mobile Station Roaming Number

The MSRN is a temporary, location-dependant ISDN number issued by the parent VLR to all MSs within its area of responsibility. It is stored in the VLR and associated HLR but not in the MS. The MSRN is used by the VLR associated MSC for call routing within the MSC/VLR service area.

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MSC

GMSC

HLR

C

D

VLR

B

gsmSCF

gsmSSF

gsmSSF

gsmSRF

Intelligent Network

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INAP

• Intelligent Network Application Part (INAP) is the signaling protocol used in Intelligent Networking. Developed by the International Telecommunication Union(ITU), IN is recognized as a global standard. Within the International Telecommunications Union, a total functionality of the IN has been defined and implemented in digestible segments called capability sets. The first version to be released was Capability Set 1 (CS-1). Currently CS-2 is defined and available. The CAMEL Application Part (CAP) is a derivative of INAP and enables the use of INAP in mobile GSM networks.

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Service Switching Point (SSP)

• Service Switching Point (SSP) is a physical entity in the Intelligent Network that provides the switching functionality. SSP the point of subscription for the service user, and is responsible for detecting special conditions during call processing that cause a query for instructions to be issued to the SCP.

• The SSP contains Detection Capability to detect requests for IN services. It also contains capabilities to communicate with other physical entities containing SCF, such as SCP, and to respond to instructions from the other physical entities. Functionally, an SSP contains a Call Control Function, a Service Switching Function, and, if the SSP is a local exchange, a Call Control Agent Function. It also may optionally contain Service Control Function, and/or a Specialized Resource Function, and/or a Service Data Function. The SSP may provide IN services to users connected to subtending Network Access Points.

• The SSP is usually provided by the traditional switch manufacturers. These switches are programmable and they can be implemented using multipurpose processors. The main difference of SSP from an ordinary switch is in the software where the service control of IN is separated from the basic call control.

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Service Control Point (SCP)

• Service Control Point (SCP) validates and authenticates information from the service user, processing requests from the SSP and issuing responses.The SCP stores the service provider instructions and data that direct switch processing and provide call control. At predefined points during processing an incoming or outgoing call, the switch suspends what it is doing, packages up information it has regarding the processing of the call, and queries the SCP for further instruction. The SCP executes user-defined programs that analyze the current state of the call and the information received from the switch. The programs can then modify or create the call data that is sent back to the switch. The switch then analyzes the information received from the SCP and follows the provided instruction to further process the call.

• Functionally, an SCP contains Service Control Function (SCF) and optionally also Service Data Function (SDF). The SCF is implemented in Service Logic Programs (SLP). The SCP is connected to SSPs by a signalling network. Multiple SCPs may contain the same SLPs and data to improve service reliability and to facilitate load sharing between SCPs. I

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Intelligent Peripheral (IP)

• Intelligent Peripheral (IP) provides resources such as customized and concatenated voice announcements, voice recognition, and Dual Tone Multi-Frequencies (DTMF) digit collection, and contains switching matrix to connect users to these resources. The IP supports flexible information interactions between a user and the network. Functionally, the IP contains the Special Resource Function. The IP may directly connect to one or more SSPs, and/or may connect to the signalling network.

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SS7 APPLICATION LAYER• At the application layer there are the following protocols• Call related

– ISDN User Part (ISUP) supports basic telephone call connect/disconnect between end offices.

• Non-call related – CAP – Camel Application Part is used to access a database ,the SCP and influence

the call

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SS7 SIGNALING ARCHITECTUREThere are 3 main elements in SS7 signaling architecture

SSP – These are SS7 capable digital switchesSTP – These are SS7 capable network elements that route incoming SS7 messages to the

correct destinationSCP – These are databases which take part in non-call related SS7 signaling

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ISUP CALL FLOWSwitch A Switch B

A dials digitsInitial Address Message (IAM) B’s phone rings..

Address Complete Message (ACM)

B Answers

Answer Message (ANM)

A disconnects

Release Message (REL)

Release Complete (RLC)

B disconnects

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ISUP

A simple call flow using ISUP signaling is as follows:Call set up: When a call is placed to an out-of-switch number, the originating SSP transmits

an ISUP initial address message (IAM) to reserve an idle trunk circuit from the originating switch to the destination switch. The destination switch rings the called party line if the line is available and transmits an ISUP address complete message (ACM) to the originating switch to indicate that the remote end of the trunk circuit has been reserved. The STP routes the ACM to the originating switch which rings the calling party's line and connects it to the trunk to complete the voice circuit from the calling party to the called party.

Call connection: When the called party picks up the phone, the destination switch terminates the ringing tone and transmits an ISUP answer message (ANM) to the originating switch via its home STP. The STP routes the ANM to the originating switch which verifies that the calling party's line is connected to the reserved trunk and, if so, initiates billing.

Call tear down: If the calling party hangs-up first, the originating switch sends an ISUP release message (REL) to release the trunk circuit between the switches. The STP routes the REL to the destination switch. If the called party hangs up first, or if the line is busy, the destination switch sends an REL to the originating switch indicating the release cause (e.g., normal release or busy). Upon receiving the REL, the destination switch disconnects the trunk from the called party's line, sets the trunk state to idle, and transmits an ISUP release complete message (RLC) to the originating switch to acknowledge the release of the remote end of the trunk circuit. When the originating switch receives (or generates) the RLC, it terminates the billing cycle and sets the trunk state to idle in preparation for the next call.

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SS7 VS OSI STACK

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Questions ?

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Quiz 11. PCM is the technique where the magnitude of the signal is sampled and digitized.

a) True b) False

2. The bit rate of DS0 or E0 PCM channel is

a) 56 Kbps b) 2 Mbps c) 64 Kbps d) 8 Khz

3. Time division multiplexing is

a. Transferring multiple lower rate channels onto higher bit rate channel

b. Sampling a signal in multiples of time

c. Using several carrier frequencies to multiplex a channel

d. Uses G.711 law

4. T Carrier is North American market and E Carrier is European

a. True b. False

5. The principle of digital switching is based on

a. Mapping IP addresses to port numbers

b. Performing layer 2 switching

c. Based on Time slot interchange

d. OSI Network layer

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Quiz 16. Which of the below is not a signaling event

a. Off hook b. On –hook c. Ringing d. conversation

7. Central Offices are usually

a. Class 4 switch b. Class 5 switch c. Classless switch d. Class 3 switch

8. What is the ISUP message that is returned when B party answers

a. ACM b) ANM c) REL d) IAM

9. Which element is not usually considered as a part of a wireless network

a. HLR b. MSC c. Router d. VLR

10. Which of the following is true of SS7 protocol

a. is an out-of-band signaling b. Uses in-band signaling c. Devises by IETF d. is based on OSI

11. Which of the following is not a function of the SCCP Layer

a. Routing to Signaling points b. Routing to subsystems c. Performing electrical properties d. Doing flow control

12. A person’s mobile number is

a. IMSI b. IMEI c. TMSI d. MSISDN

13. The IN architecture does not include

a. SSP b. SCP d. IP e. HLR

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Agenda – Session 2

Evolution of Wireless Technologies1. Comparison of SS7 & OSI stack2. 1G3. 2G4. 2.5G5. 3G6. 3.5G7. 4G8. Recap9. TDMA, FDMA, CDMA10. CDMA Basics11. GSM Architecture12. Access, Core Network13. Cellular concepts - Roaming, Registration, Handoff14. Traffic Engineering concepts15. Recap16. Quiz 2

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First Mobile radio 1924

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First Generation Systems (1G)

These were analog systemsAdvanced Mobile Phone Service (AMPS)• US trials 1978; deployed in Japan (’79) & US (’83)• 800 MHz band — two 20 MHz bands• Still widely used in US and many parts of the world• Uses FDMA

Nordic Mobile Telephony (NMT)• Launched in 1981• Sweden, Norway, Finland• Initially 450 Mhz, later in the 900 MHz band

Total Access Communication System (TACS)• Similar to AMPS,• British design in 1985

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Second Generation (2G)

• Digital Systems• Leverage technology to increase capacity

– Speech compression, digital signal processing• Greater security against fraudVariety of 2G Systems

IS-54 and IS-136 Uses Time Division Multiplexing (TDM). Introduced in 1990 in North AmericaDigital voice channels and analog control channels

IS-136Introduced in 1994 in North AmericaDigital Voice and digital control channels

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Second generation 2G (contd)GSMGSM was developed in 1982 under Conference on European Posts and

Telecommunications (CEPT) Formal standardization took place in 1989 under ETSIGSM operates in 900 MHz bandUses TDMA.

IS-95 CDMABoth IS-136 & GSM use TDMA.CDMA all users share same frequency. The signal from each user is modulated with a

separate code.Introduced in 1989 by Qualcomm, San Diego, CaliformiaDeployed in North America and Korea.In North America occupies 800 Mhz band

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AuC

MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

Um

Abis

Abis

A

A

OMC Server

Um

Interfaces between components

B

E

E

X.25

C

F

H

X.25


GPRS (2.5 G)

GPRSGPRS is an enhancement over the GSM and adds some nodes in the network to provide

the packet switched services. These network nodes are called GSNs (GPRS Support Nodes) and are responsible for the routing and delivery of the data packets to and from the MS and external packet data networks (PDN).

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GPRS Network Elements

GPRS adds 2 Network Elements to the network Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) Allows bit rates up to 170 kbps

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2.5G Architectural details


Third Generation (3G)

• IMT-200 was formed to handle higher network capacity• 144 Kbps for mobile service• 2MBps for fixed access• Operates in the 2Ghz band• The main technologies were selected• Wideband CDMA (WCDMA)• CDMA 2000 (an evolution of IS 95 CDMA)• TDD-CDMA and TD-SCDMA)

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3G Rel 99 Architecture


Benefits of 3G

• High Quality Voice ServiceThe quality of voice falls under 3G will be much higher compared to 2G services.

Enhanced content services3G users can download full music files, full movie files and other files at high speed.

Mobile Broadband 3G User can use his handset for high speed Internet any time anywhere (where connectivity is available :P)

Video Services3G user can enjoy the video call facility wherein both the caller and receiver will be able to see each other while speaking if both have 3G services and 3G enabled handsets. 3G enables its users to send Video mails and , Video clips.

Mobile TV3G users can watch TV programmes of different video channels as per his liking while on the move.

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Fourth Generation 4G

To handle even higher data throughputs we have the 4G technology1. Long Term Evolution (LTE)2. Wireless Interoperability for Microwave Access (WiMAX)3. Uses an all-IP core network4. Data rates upto 100 Mbps

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1G Technologies'

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FDMA

• Available spectrum divided into radio channels at different frequencies• In AMPS, available spectrum is divided into 30Mhz channels• One of the 30Khz channel assigned for call• 2 channels one in each direction (FDD)• Technique is known as FDD FDMA

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2G - TDMA

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TDMA

• TDMA is an assigned frequency band shared among a few users. However, each user is allowed to transmit in predetermined time slots. Hence, channelization of users in the same band is achieved through separation in time.

• Radio channel is divided into time slots,• User A assigned to time slot 1, user B to time slot 2 and so on.• We could have FDD TDMA or TDD TDMA

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Multiple radio Access techniques

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Multiple Access Methods

AMPS 30KHz carriers – Full duplex

US TDMA IS-136 & GSM Full Duplex

1.25 Mhz carriers 800/1900 Mhz Cellular/PCS Full-Duplex

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Multiple Access Techniques

• Frequency Division Multiple Access – allocates a discrete amount of bandwidth per user

• Time Division Multiple Access – allocates unique time slots for each user • Code Division Multiple Access – all users share the same frequency all the time. A

unique code assigned to each user allows it to be distinguished from other users

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Introduction to CDMA

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Code Division Multiple Access

• CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel

• CDMA uses Direct Sequence spreading, where spreading process is done by directly combining the baseband information to high chip rate binary code.

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Spread Spectrum Techniques

• Transmission of a signal has 2 characteristics – Carrier frequency– Bandwidth

Fc – carrier

bandwidth

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Spread Spectrum vs. other modulation

• Amplitude modulation : The bandwidth is twice the baseband on either side of the carrier

• Frequency modulation modulates the carrier frequency with the baseband signal• Digital modulation like QPSK give higher spectral efficiency• In spread spectrum the transmitted signal is spread using a bandwidth much larger

than that required by mixing the data and the spreading code signal.

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Spread Spectrum - Characteristics• Transmission bandwidth much larger than that of the bandwidth or rate of

the baseband data• Transmission bandwidth dependent on the rate of the code used for

spreading

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Spread Spectrum technique

1 0 1

110101110100 110101110100

001010001011 110101110100 001010001011

Spread information

Cyclic code generator

User Information

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Spread Spectrum - Techniques• Four main techniques

– Direct Sequence (DS) – carrier modulated by a digital code larger than the signal information bit rate. These systems are also called Pseudo-noise systems

– Frequency Hopping (FH) – carrier frequency shifted in discrete increments in a pattern generated by code sequence

– Time Hopping (TH) – transmission time divided into frames and frames into time slots. During each frame one and only one time slot is modulated with the message.

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Direct Sequence Spread Spectrum

Baseband modulation

PN sequence generator

Baseband de - modulation

Information bits

PN Sequence generator

Information bits

•Commonly used due to simplicity•Direct modulation of carrier using the PN sequence. •Occupies the whole available spectrum.•Modulation can be AM, FM, BPSK or QPSK•For an information rate of 10 kbps a code rate of 1Mcps producing a spread spectrum signal of 1 Mcps.*

•* chip – each bit in a PN sequence is called chip to distinguish it from information bits

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Frequency Hopping• Frequencies selected from a pre-determined group within a available spectrum and

they change in order defined by a pseudo-random sequence with characteristics similar to thermal noise

Frequency

Time

f1 f2 f3 f4 ……

Each bit in pseudo sequence called “chip” to distinguish it from data “bit”

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Frequency Hopping

Information bits

Baseband modulation

PN sequence generator

Frequency synthesizer

Baseban de -

modulation

Information bits

Frequency synthesizer

PN Sequence generator

Bandpass

filter

On the reception side the PN sequence generator defines the centre frequency of bandpass filter and the frequency for the demodulation process. The demodulation can only succeed if both the transmission and reception are synchronized.

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CDMA

• Immunity to interference and higher user capacity• Low probability of interception and jamming• Based on the IS-95 protocol standard Operates in the 900Mhz and 1900Mhz band• Work on development of CDMA standard is by the CDMA development group (CDG)

now known as cdmaOne

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Evolution of CDMA (contd.)– CDMA 2000 1XEV has 2 variants

• CDMA 2000 1XEV DO – (evolution data only) capable of delivering streaming multimedia with rates upto 2.4 Mbps in mobile environment

• CDMA 2000 1X EVDV – (evolution data and voice) capable of delivering integrated voice and data services of upto 3.09 Mbps

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Background to GSM

• 1G : Advanced Mobile Phone Service (AMPS) Analog, Circuit Switched, FDMA, FDD

• 2G : Global System for Mobile (GSM) Digital, Circuit Switched, FDMA and TDMA, FDD

• 2G : Code Division Multiple Access (CDMA) Digital, Circuit Switched, FDMA, SS, FDD

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Frequency band Uplink 890 - 915 MHz Downlink 935 - 960MHzDuplex Frequency Spacing 45MHzCarrier separation 200KHzFrequency Channels 124Time Slots /Frame(Full Rate) 8Voice Coder Bit Rate 13KbpsModulation GMSKAir transmission rate 270.833333 KbpsAccess method FDMA/TDMASpeech Coder RPE-LTP-LPC

GSM System specifications

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GSM uses paired radio channels

0 124 0 124

890MHz 915MHz 935MHz 960MHz

UPLINK

DOWNLINK

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GSM Architecture

It provides an overview of the GSM network architecture. This includes a brief explanation of the different network subsystems and a description of the functionality of the elements within each of the subsystems.

• General architecture overview• The Mobile Station (MS) Subsystem and Elements• The Base Station Subsystem (BSS) and Elements

• BTS – Base Transceiver System• BSC – Base Station Controller

• The Network Subsystem (NSS) and Elements

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• Mobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)

• Base Station Subsystem (BSS)Base Transceiver Station (BTS)Base Station Controller (BSC)

• Network Switching Subsystem(NSS)Mobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR)

Elements of a GSM Network

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Base Station Subsystem

The BSC:• Allocates a channel for the duration of a call• Maintains the call:

monitors qualitycontrols the power transmitted by the BTS or MSgenerates a handover to another cell when required

The BTS:• Provide radio access to the mobile stations• Manage the radio access aspects of the system

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Network Subsystem

Can be considered as a heart of the GSM Network. All the major activities like • Routing, • Security functions, • Call handling, charging,• Operation & maintenance, • Handover decisions,

• Various kinds of interfaces are used to communicate between the different entities. Different methods are used to optimize and provide the quality network with the minimum operating cost.

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Mobile Switching Center (MSC)

• Performs call switching • Interface of the cellular network to PSTN• Routes calls between PLMN and PSTN• Queries HLR when calls come from PSTN to mobile user• Inter-BSC Handover• Paging• Billing


2G Architecture

ISUP

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BSS

BSC

RNS

RNC

CN

Node B Node B

A IuPS

Iur

Iubis

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ME

MS

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Gs

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GnHLR

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D

E

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Gp

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SIM

SIM-ME i/f or

MSC

B

PSTNPSTN

cell

2G Architecture

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Important cellular Concepts


Registration• Every mobile in the network communicates its location, and identification to

the network through the registration process• Knowing the location allows the BTS to page the mobile when a MS terminated

call is requested.– Power up registration occurs when the MS is turned on and enter the

mobile idle state– Power down registration when turned off– Timer based registration: The MS must register according to pre-

programmed timer– Distance based registration : When it reaches a pre-specified distance

from the BTS – Zone based registration: occurs based on internal zone configuration ,

when a MS enter a new zone– Parameter change registration: Occurs when a parameter changes– Ordered registration : occurs every time the system requests

registration– Traffic channel registration: occurs when the MS registers while

requesting a traffic channel allocation

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Roaming• MSs are considered ‘home’ when they are located in their home system, where they

are registered and allowed to operate• They are roamers when they are out of their home systems• MSs have a list of locations where they are in the ‘home system’• Roaming is a general term referring to the extension of connectivity service in a

location that is different from the home location where the service was registered. • the ability for a cellular customer to automatically make and receive voice calls, send

and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network, by means of using a visited network

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Handoffs

• BS Traffic not balanced: Network monitors traffic and trigger handoffs if load not balanced among BS

• Distance limit exceeded• Pilot signal strength below threshold the MS can initiate a handoff• Power level exceeded – When the mobile has exceeded the power

threshold then either side can initiate a handoff

• Handoff involves the mobile moving to a new traffic channel of a different BS

• Types of handoff– Soft Handoff – MS has simultaneous connections with two BS before a

decision is made as to which signal is stronger before breaking the connection with the BS with the weaker signal strength (not perceived by the user)

– Hard Handoff – There is a break before the make. Connection to old traffic channel is broken before the connection to a new one is made (user hears a click)

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Authentication

• The AUC does not engage directly in the authentication process, but instead generates data known as triplets for the MSC to use during the procedure. The security of the process depends upon a shared secret between the AUC and the SIM called the Ki. The Ki is securely burned into the SIM during manufacture and is also securely replicated onto the AUC. This Ki is never transmitted between the AUC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called Kc for use in over the air communications.

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Authentication procedure

1. Algorithm id (the standard algorithms are called A3 or A8, but an operator may choose a proprietary one). When the MSC asks the AUC for a new set of triplets for a particular IMSI, the AUC first generates a random number known as RAND. This RAND is then combined with the Ki to produce two numbers as follows:

2. The Ki and RAND are fed into the A3/A8 (or other operator proprietary algorithm) and a number known as Signed RESponse or SRES is calculated.

3. The Ki and RAND are fed into a standard A5 algorithm and a number called the Kc is calculated.

4. The numbers (RAND, SRES, KC) form the triplet sent back to the MSC. When a particular IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet to the SIM. The SIM then feeds this number and the Ki (which is burned onto the SIM) into the A3/A8/proprietary algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile is allowed to attach and proceed with GSM services.

5. After successful authentication, the MSC sends the encryption key Kc to the Base Station Controller (BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the Kc itself by feeding the same RAND supplied during authentication and the Ki into the A5 algorithm.

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Authentication

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Mobility Management

• Location updating- normal, periodic, IMSI attach• Paging• Security Management

– Preventing unauthorized users- authentication– Maintaining Privacy of users- ciphering

• Providing roaming facility• MM functionality mainly handled by MS, HLR, MSC/VLR.

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Traffic Engineering


Traffic Engineering

Trunk• the telephone lines connecting one telephone switch or exchange with

another are called trunks.Calling rate (C)• The number of calls which arrive over a time interval

Holding time (H)• The average duration of a call. The duartion the telephony circuits are held

during conversation

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Traffic Calculations

• The erlang describes the total traffic volume of one hour, or 3600 seconds.

• The traffic intensity, more often called the traffic, is defined as the average number of calls in progress.

A = C x H/T

Unit: Erlang (E)A: traffic intensityC: number of calls arrivals during time TH: average holding timeT: 3600 secs /1 hr

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Traffic Problem

On average, during the busy hour, a company makes 120 outgoing calls of average duration 2 minutes. It receives 200 incoming calls of average duration 3 minutes. Find the outgoing traffic, the incoming traffic and the total traffic.

A = C x H /T

Solutionwhere T = 1 hour = 60 minutesOutgoing traffic = 120 calls x 2 minutes/ 60 minutes = 4 EIncoming traffic = 200 calls x 3 minutes/ 60 minutes =10 ETotal traffic = 4 E + 10 E = 14 E

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Traffic terms

Lost call or blocked callsIn a circuit-switched system, all attempts to make calls over a congested group of trunks

are unsuccessful. The unsuccessful call is called lost call or blocked call.

Grade of service– probability of meeting blockage is called the grade of service (B)

Example: On average, one call in 100 will be blockedB= 1/100 = 0.01

Grade of service is also the• proportion of the time for which congestion exists• probability of congestion• probability that a call will be lost due to congestion

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Traffic calculations

ExampleDuring the busy hour, 1200 calls were offered to a group of trunks and six calls were lost.

The average call duration was 3 minutes

The traffic offered = A = C1 x H/T = 1200 x 3 /60 = 60 EThe traffic carried = C2 x H/T=(1200-6) x 3 / 60 = 59.7 EThe traffic lost = B = C3 x H/T = 6 x 3 / 60 = 0.3 EGrade of service = B/A = 0.3 / 60 = 0.005The total duration of the periods of congestion = B x T = 0.005 x 3600 =18 seconds

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Wireless Network

AuC

MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

Um

Abis

Abis

A

A

OMC Server

Um

B

E

E

X.25

C

F

H

X.25

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Questions ?

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Quiz 2

1. Which of the following is not 1Ga. Based on digital technology b. AMPS,TACS c. IS-95 d. Used FDMA

2. Which is not 2Ga. GSM b. IS-95 c. NMT d. IS-136

3. GPRS was designed for handling packet dataa. True b. False

4. Which of the following is not true about 3Ga. Standardized by IM-2000 b. Speeds up 2Mbps stationary c. Based on Analog

d. Uses WCDMA, CDMA20005. Which is not an access technique

a. TDMA b. FDMA c. CDMA d. PDMA6. CDMA uses

a. Used different frequencies to multiples b. Signal sent on different time slots c. Uses psuedo-random codes to multiplex d. None of the above

7. The BSC is responsible fora. Allocates channel b. Monitors power c. Performs handover d. All of the above

8. MSC is responsible for a. Routing and switching b. charging c. Querying the HLR when call comes from PSTN d. all of

the above

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Quiz 2

9. Registration allows the BTS to page the mobile

a) True b) False

10. Roaming allows connectivity services at a place different from home network

a) True b) False

11. Handoff happens when a mobile moves from

a) one cell to another b) from one BSC to another c) from one MSC to another d) all of the above

12. Authentication does not involve

a. AuC b. MSC c. VLR d. Mobile

13. Erlang describes the traffic volume in one hour

a. True b. False

14. If 5 calls of 500 are blocked the Grade of Service (GOS) is

a. 0.01 b. 0.1 c. 100 d. None of the above

15. GSM uses TDMA with FDD

a. True b. False

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Good luck & Thank You !!!

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Tinniam V Ganesh

[email protected]

Read my blogs: http://gigadom.wordpress.com/

http://savvydom.wordpress.com/

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Wireless technologies - Part 1

Technology

north american market

camel application part

base station subsystem

north american version

subscriber identity module

mobile application part

message transfer part

service control function