Subject: SIP-INFO instead of NOTIFY

From: Blanchard Jacqueline <[email-masked]>
Date: Tue, 23 Nov 1999 11:47:32 +0100

Hi,

In PINT Session Monitoring simplest case,  where notifications are sent from
the PINT gateway to
the PINT client during a call, I would like to use the new SIP SIP-INFO 
method instead of the SUBSCRIBE/NOTIFY/UNSUBSCRIBE methods.

What do you think about this idea ?
 
Jacqueline

> Jacqueline Blanchard
	SIEMENS Réseaux Informatiques et Télécommunications
> 22300 LANNION
> 
> Phone :	+ 33 2 96 48 73 81
> Fax :	+ 33 2 96 48 74 73
> 
> Email :	[email-masked]
> 
> 
> 
> 
> 
> 

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From: Lawrence Conroy <[email-masked]>
Date: Thu, 25 Nov 1999 15:25:59 +0000

>What do you think about this idea ?

Here's my two pounds worth:

Re. Jacqueline's comments:

In summary, Yes you can, but No, you wouldn't want to this.

*   One can, apparently, send anything attached to an INFO message
     (except, perhaps, DTMF :). Thus, one could send (for example) text
     between parties to a SIP session.

*   Problem is, whether they understand the content is another matter.
     It isn't clear how one indicates that there is service status
     information inside this INFO message; all one has is a sub-part.
     Thus, the use of INFO (as it is defined at present) is going
     to be proprietary.
    
-   If you want to inter-operate, you could add some further semantics
     to the SIP INFO method. BTW, IMHO that work would need to be done
     in the SIP WG, not here, as it would require changes to a ->SIP<-
     extension. I guess the alternative is writing an an RFC for
     "application/pintstatus" (or "application/vnd.siemensfr-pintstatus").

-   Sub*scribe/Notify/Unsub*scribe was designed as a general method
     to indicate status. There's no need to guess what the content
     of the NOTIFY messages is; by definition it's status on the
     SUB*scribed session.

*   The SIP INFO method allows User-to-User signalling to be sent
     inside an existing SIP session. By definition, PINT is based on
     SIP, so it is possible for the PINT Gateway to pass back INFO
     messages. It can do this without any SUB from the Client.

     Of course, a PINT Client may not be expecting anything; the PINT
     architecture allows very simple clients to be produced (that was
     the plan :); these are akin to Web Clients in that they send a
     request and await responses to that request. They need not listen
     for any spontaneous messages to be sent back; in PINT, once the 200
     has been sent back and they've sent the ACK, that's it for the
     session. Any monitoring session is just that; another (extended)
     session. This allows very simple clients, whilst also allowing
     "full service" PINT Clients to be developed.
    
     Sending an INFO message back to these simple clients will not be
     successful; they aren't listening.
    
*   I think that it may need some analysis of security; it seems
     to me that if the implementation is done less than perfectly, it's
     an invitation to a denial of service attack. With SUB/NOT/UNSUB the
     client requests the monitoring session. This allows them to open
     pinholes to carry such information only if they need it, and
     they will know to expect notifications - they asked for them.
     This is not possible using "naked" INFO messages.
    
*   Also, how does the client stop the Gateway sending these INFO
     messages? The only way I can see to do this is to reject each
     unwanted INFO message and hope that the Gateway gets the point.

     I'm reminded of the first PIN BOF, where a similar proposal
     (un-requested information messages) was not well received...
     it was categorized as "the PSTN spamming the Internet"
All the best, Lawrence
-----------------------------------------------------------------------
| Lawrence Conroy,    | "These Opinions must be mine, 'cos if they    |
| Roke Manor Research |  were my Company's they'd pay me for them"    |
|- [email-masked]  ---+- Tel: +44 1794 833666  Fax: +44 1794 833434 --|

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