Subject: [SIP] Some clarifications on action field in Contact

From: "Albee Vimal" <[email-masked]>
Date: Tue, 9 May 2000 20:43:48 +0530

Hi
  We have some doubts on the action parameter that is associated with a
Contact field.
1.We would like to know what it means when we register with action= redirect
or proxy. Does it mean that if a registration is made with action=redirect,
then on receiving an INVITE destined to the registered location, network
server sends a 3XX response to the UAC with all the new contact locations in
the Contact field. The UAC then sends INVITE to all the new locations
mentioned in the Contact field.

2. This is valid only if an UAC can send redirected INVITE to multiple
locations. UAC while forwarding a redirected INVITE replaces the Request-URI
with the  received Contact addresses. If one of the redirected endpoints
responds with a 2XX response, the UAC will be able to forward an ACK to the
Contact field coresponding to it (since the RFC's mandates that a 2XX
response to INVITE contain a Contact field (6.13,  Pg. 39)). But is'nt it
mandatory for an endpoint sending a 6XX response to insert a Contact field
as well.

3. This is related to 2. On receiving a  >3XX response from one of the
endpoints how will the UAC identify the location to which it has to send an
ACK. i.e how would this response be matched with a request transaction,
since the request was sent to multiple destinations.

4. In "16.6 Redirects" example in the RFC we find two Cseq fields in the 302
response. We would like to know whether it is allowed to have multiple CSeq
fields.

Please clarify on these
Thanks
Albee Vimal

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 10 May 2000 18:45:35 -0400

> mentioned in the Contact field.

It doesn't have to send the INVITE to all the new locations, but besides
that, yes.

> mandatory for an endpoint sending a 6XX response to insert a Contact field

The rules here for sending ACK are the same for any other case. You
build the Route header as you normally would (consisting of the Contact
and/or Record-Route headers), and use that. If there wasn't a Contact or
Record-Route, the ACK goes to the same place the INVITE went to.

> since the request was sent to multiple destinations.

Branch id in the via header, just like a forking proxy.

> response. We would like to know whether it is allowed to have multiple CSeq

Oops. This is wrong. Only one CSeq is allowed.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
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