SIP Extensions and Features

Method Extensions

Unknown methods rejected by User Agent using 405 or 501 response
Listed in Allow header field
Proxies treat unknown methods as a non-INVITE

Header Field Extensions

Unknown header fields are ignored by user agents and proxies
Some have feature tags registered, these can be declared in a Supported or Require header field

Message Body Extensions

Unknown message body types are rejected with a 406 response
Supported types can be declared with an Accept header field
Content-Disposition indicates what to do with it

Extension must define failback to base SIP specification.

⇒ No Profiling is needed

unlike for example, Bluetooth!

Transcript

[slide155] We can also extend not only the methods, but we can extend the header fields, the bodies, but the policy is that if in doubt, fail back to the base SIP specification. So everyone has to support the base functionality.