INTRODUCTION TO SS7 SIGNALLING_p.ppt

1 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0

Signalling

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 network element (BSC, MSC and HLR)


Signalling in the old days

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Signalling operationssubscriber A /

telephone A

subscriber B /Telephone Bexchange 1 exchange 2

1. service request2. dial tone

3. provide telephone number

4. number analysis & resource reservation5. address information

6. number analysis & resource reservation

7. 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 system implementation

• 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 Points and Signalling Transfer Points

exchange 3

SP

exchange 1

SP

exchange 1

SP

STP

SP Signalling PointSTP Signalling Transfer Point

Independent,packet-orientedsignallingnetwork

SS7


Message bearers and managers


SS7 - MTP

Layer 1 Physical Connections

MessageTransfer

Part (MTP)

Signalling Message Handling

Layer 2 Data Link Control

Layer 3


SS7 - MTP / TUP / ISUP

Transport of signallingmessages within one network

Call Control messages

Layer 1

Layer 2

Layer 3

TUP

NUP

ISUP

MT

P

MSC

SP

Layer 1‘

Layer 2‘

Layer 3

TUP

NUP

ISUP

MT

P

PSTN exchange

SP

Physicalconnections Layer 1

Layer 2

Layer 1‘

Layer 2‘Data linkcontrol

Physicalconnections

Data linkcontrol

STP


Virtual connections

B

A

VirtualConnection using

“Connection Oriented”

SCCP

OriginatingSignallingPoint

SignallingTransfer Point

SignallingTransfer Point Destination

Signalling Point

MTP

MTP

MTP

SignallingTransfer Point


SS7 - SCCP


Call Control messages

Layer 1

Layer 2

Layer 3

MT

P

Exchange

SP

Layer 1‘

Layer 2‘

Layer 3

MT

P

Exchange

SP

Physicalconnections Layer 1

Layer 2

Layer 1‘

Layer 2‘Data linkcontrol

Physicalconnections

Data linkcontrol

STP

SCCP SCCPSignalling Connection &

Control Part

e.g. ISUP e.g. ISUP

Offers following services to higher layers:

• non-call related signalling via networks of different operators

• connection-orientated network service


Summary SS7 protocols - part 1

•MTP is the message transfer part. It is responsible for transferring messages from one network element to another within the same network. It consists of three sublayers.

•TUP is the user part of the messages brought by the MTP. These messages deal with setting up, supervising and clearing the call connections. It has two variations, NUP and ISUP.

•SCCP is the signalling connection control part. Its main function is to provide virtual connections and connectionless signalling.


SS7 - BSSAP


Control messages

MT

P

BSCM

TP

MSC

Physicalconnections

Data linkcontrol

Signalling Connection &Control Part

Used to• exchange requests and responses

between BSC and MSC• encapsulate messages to be

exchanged transparently between MS and MSC

Layer 1

Layer 2

Layer 3

SCCP

BSSAP

Layer 1

Layer 2

Layer 3

SCCP

BSSAP

BSSAP Base Station Subsystem Application part


SS7 - MAP and TCAP


Transaction CapabilitiesApplication Part

MT

P

GMSC

MT

P

HLR

Physicalconnections

Data linkcontrol

Signalling Connection &Control Part

Secretary function for higher layer, e.g. when the higher layer transaction consists of a set of messages, which have to be exchanged between the peer entities in an orderly way.

Layer 1

Layer 2

Layer 3

SCCP

TCAP

Layer 1

Layer 2

Layer 3

SCCP

TCAP

MAP MAPMobileApplication Part

Non-call-related requests and responses, e.g. GMSC interrogation for the MSRN.


Summary of SS7 protocols - part 2

• BSSAPBase Station Subsystem Application PartProtocol layer responsible for communicating GSM specific messages between the MSC and the BSC, and the MSC and the MS.

• MAPMobile Application PartA GSM specific protocol for non call related applications between NSS elements.

• TCAPTransaction Capabilities and Application Part Protocol layer responsible for providing service to MAP by handling the MAP transaction messages between multiple elements.


Protocol stack in the MSC

MTP

TUP NUPISUP

SCCP

BSSAPMAP

TCAP


Signalling in GSM

TDMAFDMA

LAPDm

RR

MM

CM

TDMAFDMA

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 ManagementMM Mobility Management BSSAP BSS Application PartRR Radio Resource Management SCCP Signalling Connection Control PartLAPDm Link Protocol MTP Message Transfer Part

L1

Um Abis A

TUPNUPISUS

MAP

HLR

Externalexchange


Summary of SS7 - part 1

• Signalling is the transfer of information between subscriber interface points and the network, and between different network elements to help establish a call.

• Signalling information is interchanged as standard sets of messages, and was developed and standardised into the present SS7 system.

• GSM networks need non call related signalling, which is possible with SS7.

• The SS7 used in PSTN networks is not sufficient to fulfil the signalling requirements of GSM networks, thus new GSM protocols specific were developed.


Summary of SS7 - part 2

• MTP is the basis of SS7, and it is responsible for transferring signalling messages from one element to another within the same signalling network.

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

• SCCP is needed for virtual connections and connectionless signalling

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

• MAP is needed for signalling between NSS elements.


Review Questions toReview Questions to””Introduction to SS7 Signalling“Introduction to SS7 Signalling“


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


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 CAS signalling?

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


GSM and

intelligent

network

solutions (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 GSM networks 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


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 does not both have SS7?

a) MAP.b) ISUP.c) SCCP.d) MTP.

Review


9. Which of the following pictures is correct? a) b) c) d)

Review

INTRODUCTION TO SS7 SIGNALLING_p.ppt

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