Subject: [Ecrit] Callbacks and phonebcp

From: "Perry Prozeniuk" <[email-masked]>
Date: Wed, 30 Apr 2008 15:26:07 -0400

As part of the NENA CPE IP Capable PSAP working group we have been
looking into the SIP callback information and how the PSAP will use
this.
 
In phonebcp, following references are found:
 
==============
 
   3.   The From header MUST be present and SHOULD be the AoR of the
        caller.
...
   6.   A Contact header MUST be present which MUST be globally
        routable, for example a GRUU [I-D.ietf-sip-gruu], to permit an
        immediate call-back to the specific device which placed the
        emergency call.
 
And a little later:
   5.  Either a P-Asserted-Identity [RFC3325] or an Identity header
       [RFC4474], or both, MUST be included to identify the sender.
 
=============
 
Specifically in reference to (6) above, I believe that there is a
potential issue.  The statement that the contact header MUST be globally
routable is not sufficient.  It MUST also be usable for a period of time
after the call completes.  
 
If one looks at a situation where there is a Session Border Controller
(SBC) between the SIP phone and the PSAP, the SBC may replace the
contact header with a temporary address that although is globally
routable is ONLY valid for the duration of the call.  A GRUU would
satisfy both of these conditions, however so would any other globally
routable SIP URI for the originating phone that remained valid after the
call completion.  A GRUU would be preferred.
 
 I am suggesting the the wording be strengthened somewhat to ensure that
the Contact URI MUST be usable for callback for a short period of time
after the call completes (e.g. a few minutes) and the a GRUU SHOULD be
specified.
 
Of course if the phone is disconnected, etc then the contact may not be
usable at all after the call and the other address fields (e.g. the AOR)
will need to be used for callback which may or may not reach the caller
directly.  In most cases the phone will remain operational following the
call completion and the contact information should allow the originating
phone to be reached directly.
 
Perry
 
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---

From: "DRAGE, Keith \(Keith\)" <[email-masked]>
Date: Thu, 1 May 2008 10:55:45 +0200

There is no point in writing a MUST unless you tell us what the period
of time is. How can I assess the conformance without knowing that value.
We have certainly been round that loop in 3GPP and noone has been able
to specify how long after the initial call a callback must be possible.
 
Further this is a set of CPE requirements, and the CPE does not have
complete control over whether the Contact header remains valid.
 
regards
 
Keith

________________________________

	From: [email-masked] [mailto:[email-masked]] On
Behalf Of Perry Prozeniuk
	Sent: Wednesday, April 30, 2008 8:26 PM
	To: [email-masked]
	Subject: [Ecrit] Callbacks and phonebcp

	As part of the NENA CPE IP Capable PSAP working group we have
been looking into the SIP callback information and how the PSAP will use
this.

	==============
	 
	   3.   The From header MUST be present and SHOULD be the AoR of
the
	        caller.
	...
	   6.   A Contact header MUST be present which MUST be globally
	        routable, for example a GRUU [I-D.ietf-sip-gruu], to
permit an
	        immediate call-back to the specific device which placed
the
	        emergency call.
	 
	And a little later:
	   5.  Either a P-Asserted-Identity [RFC3325] or an Identity
header
	       [RFC4474], or both, MUST be included to identify the
sender.
	 
	=============
	 
	Specifically in reference to (6) above, I believe that there is
a potential issue.  The statement that the contact header MUST be
globally routable is not sufficient.  It MUST also be usable for a
period of time after the call completes.  
	 
	If one looks at a situation where there is a Session Border
Controller (SBC) between the SIP phone and the PSAP, the SBC may replace
the contact header with a temporary address that although is globally
routable is ONLY valid for the duration of the call.  A GRUU would
satisfy both of these conditions, however so would any other globally
routable SIP URI for the originating phone that remained valid after the
call completion.  A GRUU would be preferred.
	 
	 I am suggesting the the wording be strengthened somewhat to
ensure that the Contact URI MUST be usable for callback for a short
period of time after the call completes (e.g. a few minutes) and the a
GRUU SHOULD be specified.
	 
	Of course if the phone is disconnected, etc then the contact may
not be usable at all after the call and the other address fields (e.g.
the AOR) will need to be used for callback which may or may not reach
the caller directly.  In most cases the phone will remain operational
following the call completion and the contact information should allow
the originating phone to be reached directly.
	 
	Perry