Okay, so here's an existence proof of at least one person who has been participating in SIP-related standardization for at least 3.5 years being confused about the intention of the CSeq range. If we can't even agree amongst ourselves, there's no hope that implementors will come away with a consistent view. That's a powerful argument that clarification is in order.

(I'm not necessarily saying that the party in error is Bob or Brett, simply that both have been at this for a while, and have read 3261 to mean different things. That said, I'm pretty sure that the intention is that CSeq values can go all the way to 2**32 inside a dialog.)

/a

Bob Penfield wrote:

Section 8.1.1.5 says:

  The CSeq header field serves as a way to identify and order
  transactions.  It consists of a sequence number and a method.  The
  method MUST match that of the request.  For non-REGISTER requests
  outside of a dialog, the sequence number value is arbitrary.  The
  sequence number value MUST be expressible as a 32-bit unsigned
  integer and MUST be less than 2**31.  As long as it follows the above
  guidelines, a client may use any mechanism it would like to select
  CSeq header field values.

The maximum value stated applies to ALL requests. The phrase "For
non-REGISTER requests outside of a dialog, the sequence number value is
arbitrary" refers to the requirement that REGISTER requests (for the same
Call-ID) and in-dialog requests must always have increasing CSeq numbers.
This phrase does not mean that in-dialog and REGISTER requests may exceed
the stated limit of less than 2**31.

In section 12.2.1.1, there is text that implies that the CSeq may be any
32-bit value, but this is non-normative illustrative text. The restriction
in 8.1.1.5 still applies.

cheers,
(-:bob

Robert F. Penfield
Chief Software Architect
Acme Packet, Inc.
130 New Boston Street
Woburn, MA 01801
[EMAIL PROTECTED]


----- Original Message ----- From: "Brett Tate" <[EMAIL PROTECTED]>
To: "sip-ietf" <[EMAIL PROTECTED]>
Sent: Thursday, December 09, 2004 12:53 PM
Subject: [Sip] RFC 3261: 32 bit CSeq number




I have recently observed that some vendors are reading RFC 3261 section
8.1.1.5's CSeq maximum value comments out of context.  They are interpreting
the statement to also apply to requests within dialogs.  They are not
noticing the text within sections 8 and 8.1 which indicate that these
subsections apply to requests outside of a dialog.  Is it possible to get
the sentence reworded for clarity within errata and/or a future bis?

RFC 3261 section 8.1.1.5:
"The sequence number value MUST be expressible as a 32-bit unsigned integer
and MUST be less than 2**31."



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