Subject: [SIP] Questions on section 10.1.1 of RFC2543bis

From: "Ajay Chitturi" <[email-masked]>
Date: Mon, 19 Jun 2000 19:41:39 -0700

The following is a paragraph in section 10.1.1 of the RFC2543bis draft

    When a user agent server receives a request, it checks the Call-ID
    against those of in-progress calls. If the Call-ID was found, it
    compares the tag value of To with the user's tag and rejects
    the request if the two do not match. If the From header, including
    any tag value, matches the value for an existing call leg, the
    server compares the CSeq header field value. If less than or equal
    to the current sequence number, the request is a retransmission.
    Otherwise, it is a new request. If the From header does not match
    an existing call leg, a new call leg is created.

Why is just the tag value of To compared (while the whole of From
header is compared).

Also could you please explain the scenario where the following
happens: "If the From header does not match an existing call leg, a
new call leg is created."

Thanks
Ajay.

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From: "Jo Hornsby" <[email-masked]>
Date: Tue, 20 Jun 2000 09:25:02 +0100

>     compares the tag value of To with the user’s tag and rejects

Presumably because even if UACs are generating non-unique Call-IDs,
they are far less likely to be non-unique within the callee's space
(one would hope!).

The reason the tag of the To is considered is to ensure that this
Request really is for this user; if the tag does not match, then
the callee's request probably forked, and the request is for some
other destination (along another branch).

> new call leg is created."

I guess this vaguely confirms my first paragraph.  That's a relief. &:)

 - Jo.

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 22 Jun 2000 18:00:00 -0400

> they are far less likely to be non-unique within the callee's space

No; nothing like that. I actually think the complete To field should be
included in the comparison, so as to make this consistent with the
definition of a call leg (which does include To). In practice it will
never make a difference, since, as you point out, Call-ID are unique
anyway.

> I guess this vaguely confirms my first paragraph.  That's a relief. &:)

No, this case is to support multiparty conferences, so that someone else
can join in on a call.... some more definition work is needed for this
as part of the call control work.

-Jonathan R.
-- 
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