Subject: RE: [Sip] Session Timer - Timeout on Refresh

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 5 Dec 2001 14:04:21 -0500

> -----Original Message-----
> From: Brett Tate [mailto:[email-masked]]
> Sent: Wednesday, November 28, 2001 4:44 PM
> To: [email-masked]
> Subject: RE: [Sip] Session Timer - Timeout on Refresh
> 
> 
> > > > The bis-03 draft of SIP states under Reliability
> > > > for INVITE Requests:
> > > > "If no response is received after sending seven packet
> > > > requests, processing continues as if a 481 response was
> > > > received for that request."
> > > 
> > > Would a 408 be more appropriate than a 481?
> > > This would allow the UAC to decide the 
> > > importance of the re-invite.
> > 
> > bis-05 doesn't actually have this above text 
> > anymore; it talks about client
> > transactions sending timeouts to the TU, 
> > but I couldn't find any matching
> > text that describes how the ua core or 
> > proxy cores handle the timeouts.
> > Thats a bug.
> > 
> > Assuming it generates either a 408 or 481, 
> > the spec is clear that both
> > terminate a dialog anyway, so there is no 
> > difference.
> 
> Thanks for pointing out the change in bis-05.
> Why should a 408 automatically terminate a 
> dialog?

Well, like 481, you'd send a BYE to actually terminate. But, the idea is
that something has failed badly, so you clean up.

> 
> This change will result in proxy failure 
> causing a call to be released after 
> approximately half Session-Expires instead 
> of allowing approximately half Session-Expires 
> for the proxy to recover.

What if the INVITE was needed to convey something important? Or you tried to
transfer? You can't afford to wait for an hour for the proxies to recover in
these cases. In any case, a robust system would ensure that a request was
routed to an available proxy in the event one failed, instead of waiting for
the failed proxy to come back. This is why we have SRV records. So, I don't
see this as a real problem.

-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

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