Anita Tailor wrote:
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.
Its certainly valid in *some* contexts. For instance in REGISTER and
SUBSCRIBE this is the way to terminate a registration or subscription.
Does Expires value in INVITE is modified by intermittent SIP entities
before it reaches to its destination?
According to table 2 of 3261, proxies are not permitted to add, modify,
or delete this header. But of course a B2BUA can do as it wishes.
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."/
The above is SHOULD strength. I expect you will find many UAs that don't
bother with this.
But if you are implementing the UAS, this would be a good thing to do.
There is no point in establishing a session if the caller no longer
wants it.
Paul
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