Subject: SIP Call ID

From: Shail Bhatnagar <[email-masked]>
Date: Fri, 28 May 1999 16:10:22 -0400

Is there an upper bound on the size of SIP Call-ID ? What is the 
recommended algorithm for generating the Call-ID . My understanding 
is that a GUID is generated by 
( Time stamp(8 bytes) + counter(2 bytes) + MAC address(6 bytes)).

Thanks,
-- 
Best regards,
Shail

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From: Henning Schulzrinne <[email-masked]>
Date: Fri, 28 May 1999 22:09:00 -0400

Shail Bhatnagar wrote:
> 
> Is there an upper bound on the size of SIP Call-ID ? 

The spec does not specify any, beyond the usual message-length
limitations in case of TCP. It is likely that an implementation would
either store a variable-length string or, for matching purposes, a
suitable hash value. It appears unlikely that somebody would choose a
256-byte call identifier, but it seems safer to force implementations to
deal with arbitrary string lengths rather than introduce magic numbers.
(After all, numbers should be either 0, 1 or infinity...)

> What is the

In one of the spec versions, we did use GUIDs. Indeed, the SIP page
(http://www.cs.columbia.edu/~hgs/sip/related.html) lists an Internet
draft describing how to generate one. However, since standards-track
RFCs can't reference I-D in a normative fashion, the description of how
to generate the ID was removed, with only the requirement of local or
global uniqueness remaining. Since the GUID draft would have expired
last August but is still in the I-D archives, I'm assuming that it it
wending its way through the standardization or at least publication
process. If it becomes a standard (as opposed to an informational or
experimental RFC), the next SIP RFC can cite it. If it becomes just an
informational RFC, it can probably be suggested as one possible
alternative for generating suitable IDs. See also the draft
"Recommendations for generating Message IDs" referenced on above-noted
web page for additional hints.

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 28 May 1999 22:18:46 -0400

There is no upper bound. 

There is no specific recommended algorithm for guaranteeing uniqueness.
Pick any you like so long as it meets the requirements. One possible
approach is defined in:

http://search.ietf.org/internet-drafts/draft-leach-uuids-guids-01.txt

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen