ABSTRACT
Session Initiation Protocol (SIP) is the linchpin signaling protocol in IP Multimedia Subsystem (IMS). Accordingly, SIP addresses are the key identifiers for IMS network subscribers.
However, routing at the Internet Protocol (IP) layer is based on IP addresses. So, in a sense, the endgame always entails getting to an IP address: the most basic type of identifier in an IP network. Hence, before moving on to discuss SIP addresses and other higher-layer identifiers, we briefly discuss IP addresses.
