TABLE OF CONTENTS This section introduces the basic operations of SIP using simple examples (this section does not contain any normative statements). Some of the key protocol details are contained in the appendix to this chapter; additional low-level details are found in the RFC itself.
The first example shows the basic functions of SIP: location of an end point, signal of a desire to communicate, negotiation of session parameters to establish the session, and teardown of the session once established.
Alice "calls" Bob using his SIP identity, a type of Uniform Resource Identifier (URI) called an SIP URI. It has a similar form to an email address, typically containing a username and a host name. In this case, it is sip: bob@biloxi.com, where biloxi.com is the domain of Bob's SIP service provider. Alice has a SIP URI of sip: alice@atlanta.com. Alice might have typed in Bob's URI or perhaps clicked on a hyperlink or an entry in an address book. SIP also provides a secure URI, called a SIPS URI. An example would be sips:bob@biloxi.com. A call made to a SIPS URI guarantees that secure, encrypted transport (namely, TLS-based communication) is used to carry all SIP messages from the caller to the domain of the callee. From there, the request is sent securely to the callee, but with security mechanisms that depend on the policy of the domain of the callee.
SIP is based on an HTTP-like request/response transaction model. Each transaction consists of a request that...
