Subject: [SIP] Session timer comments (2)

From: Benny Prijono <[email-masked]>
Date: Wed, 26 Apr 2000 11:55:38 +0100

>From Session Timer draft dated March 2000 (page 5):

   If no 200 OK response to a refreshing re-INVITE is 
   received before the expiration of the session, the 
   UAC SHOULD send a BYE request to terminate the call. 
   It SHOULD send this BYE slightly before   expiration 
   of the session. Ten seconds is RECOMMENDED.

I believe this paragraph is intended to deal with two different issues.
First, when the re-INVITE failed, and, second when the UAC doesn't want
to send re-INVITE to refresh the timer. 

For the first issue, ie. when the re-INVITE failed, I think the UAC
should send the BYE immediately. For the second issue, i.e if the UAC
doesn't want to refresh the timer, then it should send the BYE slightly
before the expiration of the session (10 seconds recommended).

If my interpretation above correct, then that paragraph needs to be
modified because it is confusing. And also you need to change comments
in sample call flow in page 9:

   For whatever reason, the calling UA decides not 
   to refresh. So, after 120 seconds, it sends a BYE.

The correct timeout value should be 110 seconds.

-- 
cheers,
Bennylp

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 27 Apr 2000 01:47:24 -0400

Benny Prijono wrote:
> should send the BYE immediately. 

What do you mean by failed? Generated a non-200 class response? In this
case, definitely not, since the re-INVITE can fail for legitimate
reasons, for which you don't want to hang up the call.

If you mean fail in the sense that no response is received at all, I
guess you can send a BYE immediately if thats what you want. However,
the problem may be some kind of temporary network partition, in which
case I can envision other implementations which might prefer to retry
until the expiration of the session timer. I do believe the spec should
discuss options in the case where no response is ever received for
re-INVITE (no final response, that is).

> The correct timeout value should be 110 seconds.

Right, thanks.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (732) 741-4778
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From: Benny Prijono <[email-masked]>
Date: Thu, 27 Apr 2000 12:44:01 +0100

Jonathan Rosenberg wrote:
> > ...

Quite on the contrary, I think most of the time I will disconnect the
call when non-200 response is received, because it just means
something is wrong. The only exception I can think of is when the
re-INVITE failed because glare condition happens, which in this case
the client should retry the re-INVITE.

> re-INVITE (no final response, that is).

It's a good idea to discuss the options, but I think the spec should
not recommend any actions, because this will be too specific to the
applications. Some applications (like yours?) use session-expires to
keep the call alive, while some others (like mine) use it to clean-up
resources when the remote party is suspected to be dead. The
difference is that the later is more willing to send BYE than the
first.

Thanks,

Bennylp

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 27 Apr 2000 11:34:33 -0400

Benny Prijono wrote:
> something is wrong.

Thats not a good idea. Re-invites may fail for many reasons, including
the fact that the far side doesn't want to change the media session to
what was requested. For example, if the caller wants to add a video
stream, but the server doesn't.

-Jonathan R.