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•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.
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.
• 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.
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
• 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.