Signaling System No. 7(SS7)
The SS7 signaling protocol is widely used for common channel signaling between interconnected networks. SS7 is used to interconnect most of the cellular MSCs throughout the U.S., and is the key factor in enabling autonomous registration and automated roaming in first generation cellular systems. SS7 is an outgrowth of the out-of band signaling first developed by the CCITT under common channel signaling standard, CCS No. 6
SS7 protocol architecture:
- OMAP: Operations Maintenance and Administration Part:The OMAP functions include monitoring, coordination, and control functions to ensure that trouble free communications are possible(See figure 8.6)
- ASE: Applications Service Element
- TCAP: Transaction Capabilities Application Part:The transaction capabilities application part in 587 refers to the application layer which invokes the services of the SCCP and the MTP in a hierarchical format
- SCCP: Signaling Connection Control Pan:The signaling connection control part (SCCP) provides enhancement to the addressing capabilities provided by the MTP.SCCP uses local addressing based on subsystem numbers (SSNs) to identi& users at a signaling node.SCCP provides four classes of service: two are connectionless and two are connection-oriented,
MTP: Message Transfer Part:The function of the MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end-users and the network.MTP is provided at three levels.
- Signaling data link functions MTP Level 1
- Signaling link functions MTP Level 2
- Signaling network functions MTP Level 3
- NSP: Network Service Part:The NSP provides ISDN nodes with a highly reliable and efficient means of exchanging signaling traffic using connectionless services.The NSP allows network nodes to communicate throughout the world without concern for the application or context of the signaling traffic.
- ISDNUser Part:The ISDN user part provides the signaling functions for carrier and supplementary services for voice, data, and video in an ISDN environment