The IMS: IP Multimedia Concepts And Services, Second Edition

12.2. Design principles

SIP, as part of the IETF process, is based on the Hypertext Transfer Protocol (HTTP) and the Simple Mail Transfer Protocol (SMTP). Figure 12.1 shows where SIP fits into a protocol stack.

Figure 12.1. Protocol stack.

SIP was created with the following design goals in mind:

• transport protocol neutrality – able to run over reliable (TCP, SCTP) and unreliable (UDP) protocols;

• request routing – direct (performance) or proxy-routed (control);

• separation of signalling and media description – can add new applications or media;

• extensibility;

• personal mobility.