Subject: [sipcore] SigComp and Service-Route

From: Christer Holmberg <[email-masked]>
Date: Thu, 29 Apr 2010 19:37:59 +0200

Hi,

I appologize if the following issue have been discussed and solved before.

When reading RFC 5049 (Sigcomp), the UA figures out whether the outbound
proxy supports sigcomp by looking at outbound proxie's entry in the
Service-Route in the REGISTER response.

My questions are:

1. How can the UA ensure that the outbound proxy will be listed in the
Service-Route in the first place? RFC 3608 (Service-Route) does not
mandate the registrar to insert any intermediaries in the Service-Route,
e.g based on Path. It's all based on local policy.

2. Even if the registrar would build the Service-Route based on Path,
how does it know that the Path address/port values will be
usable/routable in the UA-towards-registrar direction (Path is supposed
to be used in the registrar-towards-UA direction)? This is similar to
the Record-Route problem, and intermediaries with different network
addresses/ports per direction would have to insert "double Path".

I guess the outbound proxy could insert itself in the Service-Route, but
that is not described anywhere in RFC 5049, and it is also a SHOULD NOT
in RFC 3608.

Regards,

Christer