Subject: Re: [Sip] INFO method used for ISUP to SIP IW

From: [email-masked]
Date: Wed, 6 Jul 2005 13:35:08 EDT

In a message dated 7/6/2005 11:47:52 AM Eastern Daylight Time, 
[email-masked] writes:

> If I remember correctly, INFO follows the rules of BYE. And, a BYE cannot 
> be sent in the backword direction for an early dialog, I think.
> 

RFC 2976 says that the INFO follows the rules for BYE as contained in RFC 
2543, which is now obsolete, so where does that leave us? RFC 2543 didn't mention 
"early dialog". Can anyone say that RFC 3261 is exactly the same in this 
area?

We've already seen at least three different opinions on this question.

Mike
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---

From: xupeili <[email-masked]>
Date: Thu, 07 Jul 2005 10:54:42 +0800

Hi,

Now there are 2 questions: 

(1) When can INFO be sent? Can it be sent from callee to caller?

At the time when RFC2976 is created, "early dialog" is not introduces.
Although RFC2976 said that it follows the rules for BYE. 
I guess the indended meaning is that it should follow the rules for messages
inside dialog such as BYE.
Since it can be used to carry end-to-end information(sometimes before dialog
is confirmed like UPDATE), there is no reason to prohibit it from being sent
by callee within dialog.

Where it can be sent before early dialog is an interesting question, It may
depend on the intent of the message. 
Considering the forking issure, if it carries the information which must be
sent to the designated recipient, it`s better to send in within a dialog.

In this case, my personal opinion is that early dialog should be established
as early as possible to make UPDATE or INFO possible to be delivered. 
even there is no explicit progress indicator for ringing  or queing etc.

(2) for ISUP interworking where to encapsulate backword ISUP message like
INR? INFO or reliable 1xx?

If we agree that INFO can be sent in both direction. It may be sent either
in reliable 1xx or INFO. 

RFC3398 section 13.1 have some rule: 
"From the caller to the callee, other ISUP messages SHOULD be
   encapsulated (see [3]) inside INFO messages, even if the INVITE
   transaction is still not finished. "

"From the callee to the caller, if a message is received by a gateway
   before the call has been answered (i.e., ANM is received) it SHOULD
   be encapsulated in an INFO, provided that this will not be the first
   SIP message sent in the backwards direction (in which case it SHOULD
   be encapsulated in a provisional 1xx response). Similarly a message
   which is received on the originating side (probably in response to an
   INR) before a 200 OK has been received by the gateway should be
   carried within an INFO.  "

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
[email-masked]
Sent: Thursday, July 07, 2005 1:35 AM
To: [email-masked]; [email-masked];
[email-masked]; [email-masked]; [email-masked]
Subject: Re: [Sip] INFO method used for ISUP to SIP IW

If I remember correctly, INFO follows the rules of BYE. And, a BYE cannot be
sent in the backword direction for an early dialog, I think.

RFC 2976 says that the INFO follows the rules for BYE as contained in RFC
2543, which is now obsolete, so where does that leave us? RFC 2543 didn't
mention "early dialog". Can anyone say that RFC 3261 is exactly the same in
this area?

Mike