Subject: Re: PINT: Question to SUBSC RIBE / BYE

From: [email-masked] (Igor Faynberg)
Date: Tue, 24 Aug 1999 13:04:39 -0400

Bernie wrote:
>
>Hi,
>
>Some part of the PINT prot draft I don't understand fully:
>
>In general my question is:
>How  a BYE request to close the SUBSCR IBE session
>and  a BYE request to terminate the (phone-) call session
>are distinguished in PINT?
>
>I assume the different Call-IDs are used. Is this so?

I believe you are absolutely right. SUBSCR IBE would need another Call-ID
in order not to make BYE ambigous, if I remember the discussions of the
LA (?) meeting and subsequent decisions. But I may be wrong, so I invite
the editors and others to comment.

>...
>Sorry for the spaces within the word SUBSCR IBE, but the mailing list
>can't handle automatically messages containing this word in the first 10
>lines (see http://www.bell-labs.com/mailing-lists/pint/19992/0003.html)

Many thanks for being both observant and sensitive!

Igor

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From: Scott Petrack <[email-masked]>
Date: Tue, 24 Aug 1999 16:09:12 -0400 (EDT)

The agree that the text is less clear than it should be. Here is the
intent of all this:

1. A BYE is sent to terminate a call. Such a request also terminates any
SUBSCRIBE that was sent. 

2. The response to this BYE can contain an Expires: header. The value in
the expires header lists for how long the server will keep state about 
the call. This allows clients to send a SUBSCRIBE request later, even
after the call was terminated, in order to see how the call completed. A 
practical example would be a request to send a fax which completes
successfully. Perhaps someone would like to send a SUBSCRIBE the following
morning to check how the fax session completed.

2. If the client wishes to terminate a subscription, but NOT terminate the
call, it should send a SUBSCRIBE with an Expires: header of 0. This is
rather like how REGISTER works. A successful response will contain the
current status, and there will be no further NOTIFY sent.

Thus it is possible to terminate the receipt of NOTIFYs by sending a new
SUBSCRIBE with the same Call-ID as was in the INVITE, but with Expires:
header set to 0.

3. When it is the PINT gateway which sends the BYE, the gateway might wish
to include an Expires: header within the BYE request. This will tell the
receiver for how long the PINT gateway will retain state about the call.
Note that this BYE terminates the call, so there will be no future changes
in state. Thus, it does not matter what Exipres: header is in any future
SUBSCRIBE request -- a successful response will contain the state of the
session when it ended, and it will never change, so there will be no
further NOTIFY. 

I agree that the section 3.5.3.3 contains an error. A BYE message will
terminate the call (in addition to terminating the "monitoring" session).
The first sentence of that section should have the word "monitoring"
removed. Then section 3.5.3.3 is about the side effect of sending a BYE
and terminating a session -- that the monitoring is also terminated.

This was my intent, in any case. Does anyone disagree?

Scott

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