unity. SIP is additionally used in IP PBXs to carry calling identification, and to set up and tear down video and audio conferences. SIP is an Internet Engineering Task Force (IETF)- approved standard. In both SIP and SS7 protocols, signaling messages are carried separately from user www.TechnicalPDF.com content. In addition, they both provide common functions. Signaling-The Basis for Billing and Monitoring Signaling networks monitor traffic on networks around the clock, worldwide. When network problems are detected, alerts are sent over the signaling network to centralized Network Operations Centers (NOCs) where technicians see visual indications of alarms on computer screens. Moreover, sections of carrier networks can be quickly reconfigured from commands sent by centralized network control centers. When carriers transmit traffic to each other, signaling messages are used to identify each carrier's traffic. This is the method by which carriers bill one another for services that they provide. No carrier has facilities everywhere, SO they rely on other providers' networks outside of their coverage area. For example, a provider that sells toll-free service to customers nationwide pays a fee for each call that terminates in another carrier's coverage area. Termination refers to the traffic destination. In the preceding example, a call terminates at the subscriber's location where it is answered. Incompatibilities between Different SIP Implementations SIP is an extremely flexible protocol that offers different ways to implement many IP applications. These differing methods are referred to as Requests for Comments (RFCs). RFCs were originally used only to solicit comments when standards are being developed. Once www.TechnicalPDF.com approved by standards bodies, the final versions of standards are then published as RFCs. SIP has many RFCs, which has been a complicating factor when carriers connect with one another at peering sites and when carriers purchase new IP equipment from manufacturers that use different SIP i