Subject: [SIP] Uniqueness of call-id

From: "Eber Mello" <[email-masked]>
Date: Fri, 25 May 2001 09:33:29 -0400

Hi,

Can someone help me understand this apparent contradition on the SIP bis
spec:

How can it be possible for "two instances of a user sharing a SIP address
... make call invitations with the same Call-ID" (section 6.26) if "The
callid
MUST be a globally unique identifier and MUSTNOT be reused for later
calls" (section 6.13)? [apart from the use of call-id in the REFER method,
where the transferee uses the same call-id of the transferor for the new
call
to the transfer-target].

Thanks,

Eber Mello
SS8 Networks
Suite 500
495 March Road
Kanata, Ontario
K2K 3G1

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 30 May 2001 18:42:21 -0400

> -----Original Message-----
> From: Eber Mello [mailto:[email-masked]]
> Sent: Friday, May 25, 2001 9:33 AM
> To: Sip@Lists. Bell-Labs. Com
> Subject: [SIP] Uniqueness of call-id
> 
> 
> 
> Hi,
> 

Way back when, we were considering fully distributed multiparty conferencing
models. In these models, each participant has a call leg to each other, each
with the same Call-ID and different tags. The problem arose when a user
would join the conference call from their desk, go to the lab to check
something, and attempt to join the conference from there. The user identity
is the same, as is the Call-ID. To distinguish, the From tag was needed.

Now, since then, we have found that fully distributed multiparty
conferencing is rather hard and really not worth the trouble, so this
becomes a non-issue.

However, From tags are now mandatory in bis-03, but for a different reason.
Without them, you cannot reliably distinguish a re-INVITE in the reverse
direction from an initial INVITE, and this can cause some problems in a few
scenarios (such as a crash and restart of the caller, or a response to a
re-INVITE from an intermediary proxy that adds a tag to the To field)

-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com