RE: [Sip] From and To-header confusion in draft-ietf-sip-replaces -04.txt

["Paul D.Smith" <[e-mail]>]

Christian,
 
If I understand you correctly, you are pointing out the following.
 
If a target receives an INVITE with Replaces headers, it has to somehow use
the Replaces To/From fields to identify a dialog.  If this dialog were
originally started by the target then there may be a mapping of:
 
To field of original INVITE ==> target's idea of remote tag
From field of original INVITE ==> target's idea of local tag.
 
However if the target did not start the dialog, the mapping is reversed.
 
To field of original INVITE ==> target's idea of local tag
From field of original INVITE ==> target's idea of remote tag.
 
And your question is... how does the Replaces To/From get mapped to the
targets idea of local/remote tags?
 
Unfortunately, this can't be resolved into a simple mapping.  A third party
REFER modifying an INVITE may not know who started the dialog and so
renaming the Replaces fields makes no difference since the referrer still
doesn't know which tag to place in which field.  The target has to perform a
lookup using both mappings - often one will find a dialog and the other will
not.
 
There is a possible issue with "loopback" type dialogs where a UA, with
multiple personalities (i.e. a gateway) may have two dialogs, one in each
direction.  In this case, it may be impossible to map to a single dialog,
which is where the following sentence from page 5 of the draft is headed...
 
  "If the Replaces header field matches more than one dialog, the UA MUST
act as if no match is found."
 
Is this a correct understanding of your posting?
 
Regards,
Paul DS.
Paul D.Smith 
Network Protocols Group 
Data Connection Ltd (DCL) 
Tel: [phone]  Email: [e-mail] 
Fax: [phone]  Web:   http://www.dataconnection.com
<http://www.dataconnection.com/>  
-----Original Message-----
From: Christian Stredicke [mailto:[e-mail]]
Sent: 27 November 2003 17:45
To: SIP (E-mail)
Subject: [Sip] From and To-header confusion in
draft-ietf-sip-replaces-04.txt



Hi!

 

I think there is some from and to-header confusion in the Replaces header.

 

Depending on who initiates the call, the to and from must be exchanged.
Maybe it would be better to use the term local and remote-tag instead or to
allow mixing from and to.

 

Christian

--

Christian Stredicke

tel:[phone] (ENUM & PSTN)