Re: [Sip] Query related to Expires header with value 0 in INVITE

See below.

From: sip-bounces at ietf.org [mailto:sip-bounces at ietf.org] On Behalf Of Anita Tailor
Sent: Tuesday, December 02, 2008 5:10 AM
To: sip at ietf.org
Subject: [Sip] Query related to Expires header with value 0 in INVITE

Hi All,

I have some queries related to expires header in SIP message.

RFC 3261 Section 20.19

" The value of this field is an integral number of seconds (in decimal)
between 0 and (2**32)-1, measured from the receipt of the request"

Does this mean 0 is a valid value of Expires header ? I am confused because of "between" word here as meaning might different if "from 0 to (2**32)-1" have used.

>>> It doesn’t look like properly. See RFC 3261 Section 13.2.1

The UAC MAY add an Expires header field (Section 20.19) to limit the

validity of the invitation. If the time indicated in the Expires

header field is reached and no final answer for the INVITE has been

received, the UAC core SHOULD generate a CANCEL request for the

INVITE, as per Section 9.

So, immediately after INVITE, the UAC should generate CANCEL. But it has to wait until it gets some response.

Section 9.1

If no provisional response has been received, the CANCEL request MUST

NOT be sent; rather, the client MUST wait for the arrival of a

provisional response before sending the request.

Does Expires value in INVITE is modified by intermittent SIP entities before it reaches to its destination?

Proxies do not modify headers present in the request it receives. See section 16.6.

If yes, then what should be UAS behavior when it receives INVITE with value 0 in Expires header ? Should UAS respond with 487 ?

Section 13.1.1 [1]

"If the request is an INVITE that contains an Expires header
field, the UAS core sets a timer for the number of seconds
indicated in the header field value. When the timer fires, the
invitation is considered to be expired. If the invitation
expires before the UAS has generated a final response, a 487
(Request Terminated) response SHOULD be generated."

So the UAS should generate a 487 right away.

Thanks in Advance

Anita

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