"M. Ranganathan" wrote:
>
> Hello!
>
>
> According to what I understand, it appears that Via is used to record the
> route that a request took and for those proxies that wish to be on the
> signaling path, of the response, they can add a Record-Route with their
> own address in the list of addresses of the Record-Route header.
Via and R-R are two separate things; the former aids in responses travelling
upstream, the latter aids in the creation of a route list for *subsequent*
requests.
Proxies that field the SIP request as it is routed downstream MUST add a
Via to the Via list. The response, thus, also traverses all such proxies
that encountered the initial request.
R-R is used for *subsequent* requests. Assume the following directed graph
of an INVITE SIP request as it travels downstream:
UAC-->P1-->P2-->P3-->UAS
Also assume that P1 and P3 inserted R-R headers as the request travelled
through them.
Now, the response for the INVITE will flow in the opposite direction (foll-
owing the Via list):
UAS-->P3-->P2-->P1-->UAC
Subsequent requests, including ACK, will have the following directed graph:
UAC-->P1-->P3-->UAS
P2 was bypassed on the subsequent request since it did not R-R.
> 1. Are proxies free to designate other proxies for the response path?
I am not sure if I understand; when a proxy handles a request (and thus
inserts a Via header), it is automatically in the response path.
> 2. If this is always the case then are the Via addresses always a
> superset of the Record-Route addresses?
Nope; Via addresses have no impact on R-R (or the Route created afterwards).
Hope that helps.
Regards,
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Internet Software and eServices Group
Lucent Technologies/Bell Labs Innovations 263 Shuman Blvd., Rm 1A-413
Naperville, Illinois 60566 Voice: +1 630 224 0216 Fax: +1 630 713 0184
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