SS7 Protocol Overview The number of possible protocol stack combinations is growing. It depends on whether SS7 is used for cellular-specific services or intelligent network services, whether transportation | SS7 Protocol Overview The number of possible protocol stack combinations is growing. It depends on whether SS7 is used for cellular-specific services or intelligent network services whether transportation is over IP or is controlling broadband ATM networks instead of time-division multiplexing TDM networks and so forth. This requires coining a new term traditional SS7 to refer to a stack consisting of the protocols widely deployed from the 1980s to the present Message Transfer Parts MTP 1 2 and 3 Signaling Connection Control Part SCCP Transaction Capabilities Application Part TCAP Telephony User Part TUP ISDN User Part ISUP Figure 4-18 shows a common introductory SS7 stack. Figure 4-18. Introductory SS7 Protocol Stack Such a stack uses TDM for transport. This book focuses on traditional SS7 because that is what is implemented. Newer implementations are beginning to appear that use different transport means such as IP and that have associated new protocols to deal with the revised transport. The SS7 physical layer is called MTP level 1 MTP1 the data link layer is called MTP level 2 MTP2 and the network layer is called MTP level 3 MTP3 . Collectively they are called the Message Transfer Part MTP . The MTP protocol is SS7 s native means of packet transport. In recent years there has been an interest in the facility to transport SS7 signaling over IP instead of using SS7 s native MTP. This effort has largely been carried out by the Internet Engineering Task Force IETF SigTran Signaling Transport working group. The protocols derived by the SigTran working group so far are outside the scope of this introductory chapter on SS7. However full details of SigTran can be found in Chapter 14 SS7 in the Converged World. TUP and ISUP both perform the signaling required to set up and tear down telephone calls. As such both are circuit-related signaling protocols. TUP was the first call control protocol specified. It could support only plain old telephone service POTS calls. Most .
