Subject: [Sip] INFO message belongs only to INVITE dialog usage?

From: Nina Garaca <[email-masked]>
Date: Thu, 31 May 2007 11:19:45 +0200

Hi all,

I have read rfc2976 - The SIP INFO Method, but I haven't really 
understood that INFO message belongs only to INVITE dialog usage, which 
however draft-ietf-sipping-dialogusage-04 claims in its part 5.3:

      5.3. Matching requests to usages

   For many mid-dialog requests, identifying the usage they belong to is
   obvious.  A dialog can have at most one invite usage, so any INVITE,
   UPDATE, PRACK, ACK, CANCEL, BYE, or INFO requests belong to it.

So my, question is:
    Can INFO message  belong to other usages, besides INVITE, such are  
SUBSCRIBE  or REFER?

Thanks in advance,
Nina.

-- 
Nina Garaca
Software Development & Testing

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From: Paul Kyzivat <[email-masked]>
Date: Thu, 31 May 2007 11:20:47 -0400

My understanding is consistent with what dialogusage says - INFO is 
specific to the INVITE dialog usage. But off the top of my head I can't 
recall where that is specified.

	Paul

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From: "Gilad Shaham" <[email-masked]>
Date: Thu, 31 May 2007 16:21:03 +0100

Typically an INFO method would be part of an INVITE usage. As far as I
know the Event header is not defined for INFO. I wouldn't count on the
other end to associate the INFO request to the subscription even if you
were to include the Event header.
Basically there is no need to have INFO on a subscription usage because
all information could be passed via SUBSCRIBE and NOTIFY. Furthermore, I
have rarely seen INFO used in practice, usually used just to pass some
proprietary information.

-----Original Message-----
From: Nina Garaca [mailto:[email-masked]] 
Sent: Thursday, May 31, 2007 12:20 PM
To: [email-masked]
Subject: [Sip] INFO message belongs only to INVITE dialog usage?

Hi all,

So my, question is:

Thanks in advance,
Nina.

---

"ZESIUM mobile" d.o.o.
Valentina Vodnika 8/9
21000 Novi Sad
Serbia

---

From: Dean Willis <[email-masked]>
Date: Thu, 31 May 2007 11:05:23 -0500

On May 31, 2007, at 4:19 AM, Nina Garaca wrote:

> understood that INFO message belongs only to INVITE dialog usage,  
> which however draft-ietf-sipping-dialogusage-04 claims in its part  
> 5.3:
>
>
>    Can INFO message  belong to other usages, besides INVITE, such  
> are  SUBSCRIBE  or REFER?
>

There was IIRC no intent in the writing of RFC 2976 to restrict INFO  
to occurring within an INVITE dialog usage. So it could technically  
be used outside of one, including in non-dialog cases.

However, RFC 2976 is considered to be somewhat underspecified, and so  
far the only place we've further specified its usage is in the  
context of transporting binary data for telephony protocol tunelling.  
We have a standing consensus to NOT use it for arbitrary data at this  
time. If we were to start using it, we'd need to do something like  
the event-packages model for INFO. So don't use it, and you won't  
have to deal with this . . .

--
Dean

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From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Thu, 31 May 2007 22:44:26 +0200

Hi, 

>>   For many mid-dialog requests, identifying the usage they  belong to

>>   is obvious.  A dialog can have at most one invite usage, so 
>>   any INVITE, UPDATE, PRACK, ACK, CANCEL, BYE, or INFO requests
belong to it.
SUBSCRIBE  or REFER?
>be used outside of one, including in non-dialog cases.

Chapter 2 of 2976 says:

"The INFO method is used for communicating mid-session signaling
information along the signaling path for the call."

I think "mid-session" rules out the non-dialog cases, doesn't it?

On the other hand, chapter 4 says:

"There is potential that INFO messages could be forked by a SIP Proxy
Server."

That should not happen in a mid-dialo case, should it?

>We have a standing consensus to NOT use it for arbitrary data 
>at this time. If we were to start using it, we'd need to do something
like  
>have to deal with this . . .

Eventhough not specified, in real life it IS used for sending DTMFs
(which is also listed in 2976 as an example usage, eventhough we may
have standing consensus on something else) and "non-telephony protocol"
information. I would even use the word "de facto standard" in some
cases. However, I am not aware of any non-INVITE dialog usage.

Regards,

Christer