Subject: [Sip] RE: [Sipping] Date header field & Expires (bug #178)

From: "Peterson, Jon" <[email-masked]>
Date: Sat, 3 Nov 2001 19:07:13 -0600

I've shifted this over to the SIP WG list, since this actually raises a
couple of bis questions.

I think the idea was that a Date header separate from the Expires header
would be provided in a REGISTER for time-synchronization purposes - the Date
contains the exact time at which a request or response was sent. So
essentially, if both headers were preset the time until expiry of a
registration would be the delta between the date in the Expires header and
the date in the Date header. 

Sending absolute time in Expires is theoretically more precise than just
using an integer time, since an unknown amount of time may have passed while
the signaling message was in transit. Unless you have an external method for
synchronizing network time, you just need to send a Date header to ensure
the clocks are in parity. However, the Date header might not really help
synchronize time for the same reason - an unknown amount of time passed
while the signaling message was in transit since that Date header was
created. For low integer values and complex signaling networks this could be
problematic. In any event it isn't clear why this would be any more precise
than sending integer values.

So, Expires in absolute time format without Date gives rise to all sorts of
synchronization issues - and by supplying both Date and Expires you're
essentially specifying the delta, so you might as well have just sent an
integer value and saved yourself an extra header.

Is any implementor out there actually using absolute time format for Expires
in REGISTER? There has been a suggestion that this should be deprecated in
favor of only integer values for Expires in REGISTER (which would obviate
the need for a Date header). Does anybody use absolute time in Expires
today?

Jon Peterson
NeuStar, Inc

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: Friday, November 02, 2001 2:06 AM
> To: [email-masked]
> Subject: [Sipping] Date header field
> 
> 
> Hello all,
> 
>   I need an example of how the Date header field is used in a SIP
> REGISTER message. 
>   The date in the Expires header field indicates the Date of expiry
> of the registration. In this case, is there a need of a seperate 
> Date header field? What is the difference between the two Dates?
>   Any information regarding this would be appreciated.     
> 
> With regards,
> Radhika.
> 
> _______________________________________________
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> This list is for NEW development of the application of SIP
> Use [email-masked] for questions on current sip
> Use [email-masked] for new developments of core SIP
> 

_______________________________________________
Sip mailing list  http://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 6 Nov 2001 01:45:17 -0500

I think eliminating absolute times in the Expires header is a good thing, so
long as its possible (backwards compatibility issues). Its worth noting that
we decided to eliminate absolute times from the Session-Expires header in
the session timer extension, for these reasons exactly.

-Jonathan R.

---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

> From: Peterson, Jon [mailto:[email-masked]]
> Sent: Saturday, November 03, 2001 8:07 PM
> To: [email-masked]'; [email-masked]'
> Subject: [Sip] RE: [Sipping] Date header field & Expires (bug #178)
> 
>