Subject: Registrar authentication response ; CSeq contiguity

From: Robert Sparks <[email-masked]>
Date: Thu, 27 May 1999 12:38:01 -0500

Local discussions have raised a pair of questions:

1) In the simple scenario of a UAC interacting directly with a
registrar, if the registrar decides authentication is required
for a request, it MAY return a 401 response(section 14.1). Could
it choose to return a 407 instead? (In other words, could a registrar
be considered a proxy rather than an end recipient of the request?)

2) Should CSeq be contiguous over {UAC,CallId} or {UAC,CallId,To,From}. If
the former, is the only rationale behind the contiguous requirement to
ensure
a large CSeq space? If the latter, has it been discussed what a UAS might do
if it detected a gap?

Robert Sparks
[email-masked]

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 28 May 1999 01:21:53 -0400

> be considered a proxy rather than an end recipient of the request?)

Probably this would work, but why do you want to do this? The registrar
is not a proxy, its a registrar. It should respond with a 401.

> a large CSeq space? If the latter, has it been discussed what a UAS might do

Its unique over the {UAC,CallID,To,From}. What this basically means is
that if A calls B, requests from B to A use a *different* CSeq space
from those used in the A to B requests. 

What to do if there is a gap:

> A user agent server MUST remember the highest sequence number for any
>    INVITE request with the same Call-ID value. The server MUST respond
>    to, and then discard, any INVITE request with a lower sequence
>    number.

This paragraph is also not clear on two important points. First, I
believe the response to a misordered request should be an error response
(probably 500). This paragraph just says respond, not what the response
is. I think the 500 here is important, since if it just responds with a
200, but ignores it, you can get inconsistent session states (in the
case of re-INVITE) at the UAC and UAS. 

Second, it says you remember the CSeq for any INVITE with the same
Call-ID. This should read, "Call-ID, To and From", as I mention above.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
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High Speed Networks Research                Holmdel, NJ 07733
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