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)
2 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
Signalling in the old days
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3 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
4 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
5 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
6 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
Message bearers and managers
7 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
SS7 - MTP
Layer 1 Physical Connections
MessageTransfer
Part (MTP)
Signalling Message Handling
Layer 2 Data Link Control
Layer 3
9 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
10 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
Virtual connections
B
A
VirtualConnection using
“Connection Oriented”
SCCP
OriginatingSignallingPoint
SignallingTransfer Point
SignallingTransfer Point Destination
Signalling Point
MTP
MTP
MTP
SignallingTransfer Point
11 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
SS7 - SCCP
Transport of signallingmessages within one network
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
12 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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.
13 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
SS7 - BSSAP
Transport of signallingmessages within one network
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
14 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
SS7 - MAP and TCAP
Transport of signallingmessages within one network
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.
15 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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.
16 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
Protocol stack in the MSC
MTP
TUP NUPISUP
SCCP
BSSAPMAP
TCAP
17 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
18 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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.
19 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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.
20 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
Review Questions toReview Questions to””Introduction to SS7 Signalling“Introduction to SS7 Signalling“
21 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
22 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
23 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
24 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
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
25 © NOKIA Introduction to SS7 Signalling/ 6-66868/ v 2-0
9. Which of the following pictures is correct? a) b) c) d)
Review
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