5 SS7 Signalling

8/9/2019 5 SS7 Signalling

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SS7 SIGNALLING IN GSM


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ObjectivesAt the end of the module the student is able to:

Define the term signalling

Describe the SS7 protocol stack and its functions

Identify the SS7 protocol stacks implemented in each GSM networkelement (BSC, MSC and HLR)

Signalling


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%#!&?:^*(%/=

Signalling in the old days


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subscriber A /telephone A

subscriber B /Telephone Bexchange 1 exchange 2

1. service request

2. dial tone

3. provide telephone number

4. numberanalysis &resourcereservation5. address information

6. numberanalysis &resourcereservation7. set-up message

8. set-up confirmation

9. ringing

10. alert message

12. ringing tone

11. address completemessage

13. connect message14. connect message

15. Conversation

Signalling operations


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Set of standard messages Many ways of implementation

Evolution of multiple systems

Problems in compatibility

Development of Channel Associated Signalling

Good for low traffic only Bottleneck and waste of bandwidth Development of SS7

High capacity Signalling in the absence of a call possible

Signalling system implementation


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exchange 3

SP

exchange 1

SP

exchange 1

SP

STP

P Signalling Point

TP Signalling Transfer Point

Independent,packet-orientedsignallingnetwork

SS7

Signalling Points and Signalling Transfer Points


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Message bearers and managers


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Layer 1 Physical Connections

MessageTransfer

Part (MTP)

Signalling Message Handling

Layer 2 Data Link Control

Layer 3

SS7 - MTP


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Transport of signallingmessages within one network

Call Controlmessages

Layer 1

Layer 2

Layer 3

TUP

NUP

ISUP

MTP

MSC

SP

Layer 1

Layer 2

Layer 3

TUP

NUP

ISUP

MTP

PSTN exchange

SP

Physicalconnections Layer 1

Layer 2

Layer 1

Layer 2Data linkcontrol

Physicalconnections

Data linkcontrol

STP

SS7 - MTP / TUP / ISUP


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B

A

VirtualConnection using

ConnectionOriented

SCCP

OriginatingSignallingPoint

Signalling

Transfer Point

SignallingTransferPoint Destination

Signalling Point

MTP

MTP

MTP

SignallingTransferPoint

Virtual connections


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Call Controlmessages

Layer 1

Layer 2

Layer 3

MTP

Exchange

SP

Layer 1

Layer 2

Layer 3

MTP

Exchange

SP

Physicalconnections Layer 1

Layer 2

Layer 1

Layer 2Data linkcontrol

Physicalconnections

Data linkcontrol

STP

SCCP SCCP

Signalling Connection &Control Part

e.g. ISUP e.g. ISUP

Offers following services to higherlayers:

non-call related signalling vianetworks of different operators

connection-orientated networkservice

SS7 - SCCP


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MTPis the message transfer part. It is responsible for

transferring messages from one network element to anotherwithin the same network. It consists of three sublayers.

TUPis the user part of the messages brought by the MTP. Thesemessages deal with setting up, supervising and clearing the callconnections. It has two variations, NUP and ISUP.

SCCPis the signalling connection control part. Its main functionis to provide virtual connections and connectionless signalling.

Summary SS7 protocols - part 1


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Controlmessages

MTP

BSC

MTP

MSC

Physicalconnections

Data linkcontrol


Used to exchange requests and responses

between BSC and MSC encapsulate messages to be

exchanged transparently betweenMS and MSC

Layer 1

Layer 2

Layer 3

SCCP

BSSAP

Layer 1

Layer 2

Layer 3

SCCP

BSSAP

AP Base Station Subsystem Application part

SS7 - BSSAP


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Transaction CapabilitiesApplication Part

MTP

GMSC

MTP

HLR

Physicalconnections

Data linkcontrol


Secretary function for higher

layer, e.g. when the higherlayer transaction consists of aset of messages, which have tobe exchanged between thepeer entities in an orderly way.

Layer 1

Layer 2

Layer 3

SCCP

TCAP

Layer 1

Layer 2

Layer 3

SCCP

TCAP

MAP MAPMobile

Application Part

Non-call-related requests andresponses, e.g. GMSC

interrogation for the MSRN.

SS7 - MAP and TCAP


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BSSAPBase Station Subsystem Application Part

Protocol layer responsible for communicating GSM specificmessages between the MSC and the BSC, and the MSC and theMS.

MAPMobile Application Part

A GSM specific protocol for non call related applicationsbetween NSS elements.

TCAPTransaction Capabilities and Application PartProtocol layer responsible for providing service to MAP by

handling the MAP transaction messages between multipleelements.

Summary of SS7 protocols - part 2

P l k i h MSC


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MTP

TUPNUP

ISUPSCCP

BSSAP

MAP

TCAP

Protocol stack in the MSC

Si lli i GSM


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TDMA

FDMA

LAPDm

RR

MM

CM

TDMA

FDMA

LAPDm

RR

L1

LAPD

BTSM

LAPD

BTSM

RR

MTP

SCCP

BSSAPP

MM

CM

BSSAP

TCAP

SCCP

MTP

MS MSC

BSCBTS

CM Connection Management BTSM Base Transceiver Station Management

MM Mobility Management BSSAP BSS Application Part

RR Radio Resource Management SCCP Signalling Connection Control Part

LAPDm Link Protocol MTP Message Transfer Part

L1

Um Abis A

TUPNUP

ISUS

MAP

HLR

Externalexchange

Signalling in GSM

S f SS7 t 1


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Signalling is the transfer of information between subscriber

interface points and the network, and between different networkelements to help establish a call.

Signalling information is interchanged as standard sets ofmessages, and was developed and standardised into the presentSS7 system.

GSM networks need non call related signalling, which is possiblewith SS7.

The SS7 used in PSTN networks is not sufficient to fulfil thesignalling requirements of GSM networks, thus new GSM protocolsspecific were developed.

Summary of SS7 - part 1

S f SS7 t 2


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MTP is the basis of SS7, and it is responsible for transferring

signalling messages from one element to another within the samesignalling network.

TUP/ISUP are the user parts of MTP that handle call control.

SCCP is needed for virtual connections and connectionlesssignalling

BSSAP is used for signalling between MSC - BSC and MSC - MS.

MAP is needed for signalling between NSS elements.

Summary of SS7 - part 2


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Review Questions to

Introduction to SS7Signalling

Review


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a) It supported only call related signalling.

b) It required one signalling channel for every

PCM line.c) It was not possible to have many different

signalling messages.

d) All of the above.

1. Which of the following is not a signalling function?

2. Which of the following was a drawback of CAS signalling?

a) To analyse the dialled digits.b) To digitise the user's speech before

transmission.

c) To make speech path connections.

d) To inform the user of the progress of the call.

Review

Review


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a) The need to supervise a call.

b) The need to make circuit reservations.c) The need to clear connections when the call

is over.

d) The need to transfer charging information.

3. Which of the following are advantages of SS7 over CASsignalling?

4. Which of the following is not a need for SS7 signalling?

a) It can send call set-up messages.

b) One signalling channel can support 10 000

traffic channels.

c) It can support non-call-related signalling.d) All of the above.

Review

Review


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GSMand

intelligentnetwor

ksolutions (IN)

a) MTP, SCCP.

b) MTP, ISUP.

c) MTP, TUP.

d) MTP, SCCP, TCAP, MAP.

5. Which of the following signalling requirements is specific to GSMnetworks only?

6. Which of the following is not a need for SS7 signalling?

a) The ability to reserve circuits in the outgoing

direction.

b) The ability of one signalling channel to handle calls

in other physically different cables.

c) The ability to transport service dependent

messages across switching exchanges.

d) The ability to perform non-call-related signalling

procedures. .

Review

Review


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a) MSC, HLR.

b) BSC, HLR.

c) MSC, BSC.

d) BTS, HLR.

7. Which of the following SS7 protocols is specific to GSM

networks only?

8. Which pair of network elements in the GSM network doesnot both have SS7?

a) MAP.

b) ISUP.

c) SCCP.

d) MTP.

Review

5 SS7 Signalling

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