Subject: RE: [Sipping] b2bua and cc-transfer

From: "Ian Elz \(CV/ETL\)" <[email-masked]>
Date: Wed, 2 May 2007 17:22:10 +0200

Peter,
 
I only included the call-id mapping as an example. I showed the call-id
as mapped in the original call to highlight the issue with the b2bua in
that the Replaces header will need to be different on either side of the
b2bua. It may well be that the to-tag and from-tag have also been mapped
and they will need to be changed across the b2bua as well.
 
If a REFER is sent on a new dialog, e.g. to add a new participant to a
conference, then the Target-dialog header may have to be used.
 
Unfortunately this will be different depending upon where the Focus
contact ( as sent from the b2bua) is included in the REFER.
 
If the REFER is for a dial in conference and the conference focus
contact is included in the Refer-to header then the target-dialog must
be as a header parameter of the Refer-To.
 
If the REFER is for a dial out conference and the conference focus
contact is in the Request URI then a target-dialog header must be used.
 
In the case where an existing dialog is being replaced in either of
these cases there is no need to include both the Replace and
Target-dialog as they convey the same information.

Ian Elz 

Office: + 44 24 764 35256 
gsm: +44 7801723668 
[email-masked] 

________________________________

From: Peter Musgrave 
Sent: Monday, April 30, 2007 10:13 AM
To: [email-masked]'; [email-masked]';
[email-masked]'
Cc: [email-masked]'
Subject: RE: [Sipping] b2bua and cc-transfer

Hi all, 

In addition to mapping the Call Id and the contact header, the B2B will
need to map the to-tag and from-tag information in the Replaces header. 

According to RFC3891 Section 3:

The User Agent Server

(UAS) matches the to-tag and from-tag parameters as if they were tags
present in an incoming request.  In other words, the to-tag parameter is
compared to the local tag, and the from-tag parameter is compared to the
remote tag.

This introduces an additional wrinkle. 

+-----+             +------+           +------+            +-----+

|UA -A|             | UA-B |           |b2bua |            |UB-C |

+-----+             +------+           +------+            +-----+

                                     maps: call-id

                                           Contact

Assume C calls B and establishes a dialog. B then calls A and sends A a
REFER to C with a Replaces telling it to replace the dialog C has with
B. So the B2B must adjust the call id, and ensure that the to-tag in the
resulting INVITE with replaces matches the local tag provided by C in
it's initial call to B (i.e. the tag in the From header). 

The other scenario is as above but when the initial call is caused by B
calling C. In this case C's local tag will be in the To: header. When
the transfer occurs and an INVITE with replaces goes through to C, the
B2B now needs to ensure the to-tag value comes from the To: header in
the initial dialog. 

As long as the B2B keeps track of "local" and "remote" tags for each
dialog, this mapping should be fairly straight-forward. 

Peter

_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: "Peter Musgrave" <[email-masked]>
Date: Wed, 2 May 2007 10:01:54 -0600

Hi Ian, 

Fair enough. I wasn't sure what level of detail was appropriate. 

It might be useful to include a list of headers which will require
careful inspection and possible mapping in e.g.
draft-marjou-sipping-b2bua

The REFER case has raised several issues (and I had not thought of the
target-dialog issue). 

I'm sure there are other headers which even in a transparent B2B will
need examination and mapping. It would be great to have a list
somewhere...

Off the top of my header any messages as part of the dialog event
package would need mapping (and require inspection of the XML content).

Ah, the joys of being a B2BUA.

Peter

From: Ian Elz (CV/ETL) [mailto:[email-masked]] 
Sent: Wednesday, May 02, 2007 11:22 AM
To: Peter Musgrave
Cc: [email-masked]
Subject: RE: [Sipping] b2bua and cc-transfer

Peter,

Ian Elz 

 

From: Peter Musgrave 

Hi all, 

The User Agent Server

                                     maps: call-id

                                           Contact

Peter

---

From: "Xavier Marjou" <[email-masked]>
Date: Wed, 2 May 2007 18:13:04 +0200

> It might be useful to include a list of headers which will require careful
> inspection and possible mapping in e.g. draft-marjou-sipping-b2bua

I think it's a good idea. I will also include a section for the REFER
case based on the content of this thread.

> I'm sure there are other headers which even in a transparent B2B will need
> examination and mapping. It would be great to have a list somewhere…

What about: In-Reply-To, Join, Refer-To, Replaces, and Target-Dialog ?

> Off the top of my header any messages as part of the dialog event package
> would need mapping (and require inspection of the XML content).

I will also add that one.

---

From: "Peter Musgrave" <[email-masked]>
Date: Wed, 2 May 2007 10:21:46 -0600

Hi Marjou, 

Great. It will be useful to have this recorded in the b2bua draft

>What about: In-Reply-To, Join, Refer-To, Replaces, and Target-Dialog ?

Perhaps also:
History-Info (if reqUri is retargeted by b2b)

Also, depending on exactly how transparent the B2B is it may need to
adjust the contents of Supported, Allow and Allow-Events...

Peter

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Xavier Marjou
Sent: Wednesday, May 02, 2007 12:13 PM
To: Peter Musgrave
Cc: Ian Elz (CV/ETL); [email-masked]
Subject: Re: [Sipping] b2bua and cc-transfer (and marjou-sipping b2bua)

> It might be useful to include a list of headers which will require
careful

> I'm sure there are other headers which even in a transparent B2B will
need
> examination and mapping. It would be great to have a list somewhere...

> Off the top of my header any messages as part of the dialog event
package

---

From: Paul Kyzivat <[email-masked]>
Date: Wed, 02 May 2007 17:21:51 -0400

> Ah, the joys of being a B2BUA.

If more people realized the complexities of implementing a B2BUA 
correctly, maybe there would be less inclination to use B2BUAs.

	Paul

---

From: "Ian Elz \(CV/ETL\)" <[email-masked]>
Date: Thu, 3 May 2007 13:25:40 +0200

Peter, Xavier

I was going to ask Xavier, off list (I did not wish to hijack his
draft), if he thought that his draft would be a suitable place to
capture the b2bua requirements and the associated actions required by
UAs to support networks with b2bua functionality. I don't think that
there is anything new for the UAs but some of the functionality should
be highlighted by examples.

I must admit that I have not yet looked at In-Reply-To, Join and History
as my main focus has been on transfer and conference. These headers will
need to be examined though so that any proposal will work with all
impacted headers.

The issues relating to Supported, Allow and Allow-Events is different
from the mapping and routing issues which I have raised but do need to
be considered.

I can send some sequences which show the Refer-To ?Replaces for
consideration. Is it OK if I send these as pictures in an attachment
(e.g. rtf format) as I currently have them in visio and converting them
to text as normally put into drafts will take time and I would prefer
not to do this until we have some agreement.

Ian Elz

-----Original Message-----
From: Peter Musgrave [mailto:[email-masked]] 
Sent: 02 May 2007 17:22
To: Xavier Marjou
Cc: Ian Elz (CV/ETL); [email-masked]
Subject: RE: [Sipping] b2bua and cc-transfer (and marjou-sipping b2bua)

Hi Marjou, 

Perhaps also:

Peter

-----Original Message-----

careful

need

package