Subject: [Sip] What exactly is "response context"?

From: "Patrick Lam" <[email-masked]>
Date: Tue, 15 Apr 2003 10:05:57 +0800

Dear all:

What exactly is "response context" being mentioned in RFC 3261 (p.107)?  Why
would a response context contain multiple responses (so that a proxy has to
choose the best one)?  Should there be only one appropriate response to be
forwarded by the proxy at any particular time?  For example, after receiving
a response downstream, the proxy would (at least for most cases) forward
this same response upstream, right?

I think I am missing some important concept about response context here.
Can someone please explain?

Thanks very much in advance.

Patrick Lam

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 14 Apr 2003 23:08:38 -0400

It is defined in section 16.6:

>   A stateful proxy must have a mechanism to maintain the target set as
>    responses are received and associate the responses to each forwarded
>    request with the original request.  For the purposes of this model,
>    this mechanism is a "response context" created by the proxy layer
>    before forwarding the first request.

When a proxy forks, it will get responses for each forked response. 
Those are held in the response context.

-Jonathan R.

Patrick Lam wrote:
> Dear all:
> 
> What exactly is "response context" being mentioned in RFC 3261 (p.107)?
> Why would a response context contain multiple responses (so that a proxy
> has to choose the best one)?  Should there be only one appropriate
> response to be forwarded by the proxy at any particular time?  For
> example, after receiving a response downstream, the proxy would (at
> least for most cases) forward this same response upstream, right?
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Scientist                             Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: "Patrick Lam" <[email-masked]>
Date: Tue, 15 Apr 2003 17:37:46 +0800

Understood.

But why does the proxy not forward all the responses to the UAC (each of
them will be identified by the dialog ID), and let the UAC handle the
responses separately?  E.g. someone in the conference requiring
authentication may send 401, while the others are all sending 2xx's.  If
the UAC also receives 401 from that particular user, it can follow-up
with appropriate authentication.

From my gut feeling, choosing the *best* response among the response
context is just not a perfect way to handle forking.  

I must be wrong, however.

Patrick Lam

> -----Original Message-----
> From: Jonathan Rosenberg [mailto:[email-masked]]
> Sent: Tuesday, April 15, 2003 11:09 AM
> To: Patrick Lam
> Cc: [email-masked]
> Subject: Re: [Sip] What exactly is "response context"?
>

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 15 Apr 2003 23:46:30 -0400

Patrick Lam wrote:
> responses separately? 

This was a long-time-ago design decision, to avoid a flood of non-200 
responses in cases where there was wide forking. It has been in the 
specs since rfc2543.

-Jonathan R.