Chapter 3. The Role of SS7 The purpose of this chapter is to introduce Signaling System No. 7 (SS7/C7) and give the reader an indication of how it affects the lives of nearly two billion people globally. | Chapter 3. The Role of SS7 The purpose of this chapter is to introduce Signaling System No. 7 SS7 C7 and give the reader an indication of how it affects the lives of nearly two billion people globally. The chapter begins by providing a brief introduction to the major services that SS7 C7 provides and explains how the protocol has been and will continue to be a key enabler of new telecommunication services. It concludes with an explanation of why SS7 C7 is a cornerstone of convergence. SS7 C7 is the protocol suite that is employed globally across telecommunications networks to provide signaling it is also a private behind the scenes packet-switched network as well as a service platform. Being a signaling protocol it provides the mechanisms to allow the telecommunication network elements to exchange control information. AT T developed SS7 C7 in 1975 and the International Telegraph and Telephone Consultative Committee CCITT 109 adopted it in 1980 as a worldwide standard. For more information on the standards bodies see Chapter 2 Standards. Over the past quarter of a century SS7 has undergone a number of revisions and has been continually enhanced to support services that are taken for granted on a daily basis. SS7 C7 is the key enabler of the public switched telephone network PSTN the integrated services digital network ISDN intelligent networks INs and public land mobile networks PLMNs . Each time you place and release a telephone call that extends beyond the local exchange SS7 C7 signaling takes place to set up and reserve the dedicated network resources trunk for the call. At the end of the call SS7 C7 takes action to return the resources to the network for future allocation. TIP Calls placed between subscribers who are connected to the same switch do not require the use of SS7 C7. These are known as intraoffice intraexchange or line-to-line calls. Each time a cellular phone is powered up SS7 C7-based transactions identify authenticate and register the subscriber.
