Subject: [Sip] Question regarding Section 13.3.1 item 1.. ??

From: "Venkatesh Venkataramanan" <[email-masked]>
Date: Sun, 10 Feb 2002 16:11:20 -0800

Sorry. Let me re-phrase my question !

The earlier versions of the bis allowed "Expires" header to be expressed as
absolute time (basically equivalent to the "Date" header). This caused
interoperability problems when UA's were out of sync as regards time
(section 29.1 talks about this). To alleviate this problem, Expires now use
"relative time". Now, as regards INVITE processing, per section 13.3.1 of
bis07,

"If the request is an INVITE that contains an Expires header field the UAS
core inspects this header field. If the INVITE has ALREADY expired, a 487
response SHOULD be generated."

And this part (ascertaining if an INVITE has "already" expired) is not valid
anymore. The reason being:

There is no way for the UAS to accurately determine if the request has
expired when it receives the request, if the two UA's under consideration
were out of sync as regards time.

Say UA1 and UA2 are out-of-sync by 10 minutes (UA1 is ahead of UA2). Say UA2
initiates an INVITE to UA1 with the following information with Expires
header set to 180:

INVITE ....
Date: Sat, 10 Feb 2002 10:20:00 PST
Expires: 180
...

When UA2 receives this request, the INVITE has already expired per UA2's
time ( as it is 10 minutes ahead of UA1). Hence it generates a 487 Response
which is the problem...

Regards,
Venkatesh

-----Original Message-----
From: Sankaran Narayanan [mailto:[email-masked]]
Sent: Saturday, February 09, 2002 5:57 PM
To: Venkatesh Venkataramanan
Cc: [email-masked]'
Subject: Re: [Sip] Clarification as regards Expires Header in INVITE

i think if there is a Date header, Date + Expires < Current will
give whats needed.

On Sat, 9 Feb 2002, Venkatesh Venkataramanan wrote:

> Hi,
>
> Per bis07, section 24.19, the Expires header is an integer number in
> seconds. However section 13.3.1 of the bis (Processing of INVITE)
indicates
> that an UAS is supposed to respond with a 487 response for the INVITE if
the
> INVITE has "Expired". How would an UAS decide if the request has "expired"
> if the Expires header is not expressed more like a "Date" header in the
> request?
>
> Regards,
> Venkatesh
>
>
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_______________________________________________
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---

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 11 Feb 2002 15:44:47 -0500

> were out of sync as regards time.

Yes, this is a good point. It could have Expires: 0, but that is not all
that useful. I fixed.

> time ( as it is 10 minutes ahead of UA1). Hence it generates a 487

No, no; the expires is not taken relative to the Date, its taken
relative to the local time at the UA. What text leads you to believe its
relative to any Date header? I will try to clarify the exact process.

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
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