Signaling System No.7 Protocol Architecture And Sevices part 46

Interfaces and Protocols The previous section introduced GSM network architecture, and this section introduces the SS7/C7 protocols that are used. It also discusses interfaces, because different protocols
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Signaling System No.7 Protocol Architecture And Sevices part 46Interfaces and ProtocolsThe previous section introduced GSM network architecture, and this sectionintroduces the SS7/C7 protocols that are used. It also discusses interfaces, becausedifferent protocols are used on different interfaces. The SS7/C7 protocols MTP,SCCP, TUP, ISUP are protocols that were used before digital wireless networkswere available. The final part of this section introduces SS7/C7 protocols that werespecifically developed for GSM.Table 12-2 summarizes the interfaces and protocols that are used in GSM. Table 12-2. GSM Interfaces and ProtocolsInterface Between DescriptionUm MS-BSS The air interface is used for exchanges between a MS and a BSS. LAPDm, a modified version of the ISDN LAPD, is used for signaling.Abis BSC-BTS This is a BSS internal interface that links the BSC and a BTS; it has not been standardized. The Abis interface allows control of radio equipment and radio frequency allocation in the BTS.A BSS-MSC The A interface is between the BSS and the MSC. It manages the allocation of suitable radio resources to the MSs and mobility management. It uses the BSSAP protocols (BSSMAP and DTAP).B MSC-VLR The B interface handles signaling between the MSC and the VLR. It uses the MAP/B protocol. Most MSCs are associated with a VLR, making the B interface internal. Whenever the MSC needs to access data regarding an MS that is located in its area, it interrogates the VLR using the MAP/B protocol over the B interface.C GMSC- The C interface is between the HLR and a GMSC or a HLR or SMSC. Each call that originates outside of GSM (such as SMSG- an MS terminating call from the PSTN) must go through HLR a gateway to obtain the routing information that is required to complete the call, and the MAP/C protocol over the C interface is used for this purpose. Also, the MSC can optionally forward billing information to the HLR after call clearing.D HLR-VLR The D interface is between the HLR and VLR, and uses the MAP/D protocol to exchange data related to the location of the MS and subsets of subscriber data.E MSC-MSC The E interface connects MSCs. The E interface exchanges data that is related to handover between the anchor and relay MSCs using the MAP/E protocol. The E interface can also be used to connect the GMSC to an SMSC.F MSC-EIR The F interface connects the MSC to the EIR and uses the MAP/F protocol to verify the status of the IMEI that the MSC has retrieved from the MS.G VLR-VLR The G interface interconnects two VLRs of different MSCs and uses the MAP/G protocol to transfer subscriber information—for example, during a location update procedure.H MSC- The H interface is located between the MSC and the SMSG SMSG and uses the MAP/H protocol to support the transfer of short messages. Again, GSM as well as ANSI-41 is unknown, but H in ANSI-41 is used for HLR–AC interface.I MSC-MS The I interface is the interface between the MSC and the MS. Messages exchanged over the I interface are transparently relayed through the BSS.In terms of the physical layer, the air interface (MS-BTS) uses RF radiotransmission. The A-bis interface (BTS-BSC) uses 64 kbps over whatever mediumis most convenient for installation: wire, optical, or microwave. All other interfacesin the GSM system use SS7/C7s MTP1 at the physical layer.The data link layer that is used at the air interface (MS-BTS) is LAP-Dm; LAP-Dis the data link layer that is used at the A-bis interface (BTS-BSC). All otherinterfaces in the GSM system use SS7/C7s MTP2 at the data link layer.The air interface (MS-BTS) and the Abis interface (BTS-BSC) do not have anetwork layer. All other interfaces in the GSM system use SS7/C7s MTP3 andSCCP at the network layer.The transport, session, and presentation layers are not used in SS7/C7—thesefunctions are grouped together at the application la ...