User Agent
Click on the red underlined text to get to the source
... URI in the Contact header field if
it is a user agent client. If the client is a proxy, it SHOULD add
...
... Record-Route header
field.
If a user agent client sends a compressed request, it SHOULD add the
parameter comp=sigcomp to the URI ...
... Note that receiving incoming requests (even initial INVITEs)
compressed is not a problem, since user agents can REGISTER a SIP URI
...
... URI of the next upstream
(closer to the user agent client) hop in the route set. If this URI
...
... header field.
The same way, a user agent server SHOULD add comp=sigcomp to the
Contact header field ...