Subject: [Sip] History-Info: UA loose route versus Target header

From: "Mary Barnes" <[email-masked]>
Date: Thu, 13 Mar 2008 10:34:13 -0500

Per my comments at the microphone, here's my assessment of the
difference between the two documents as they apply to History-Info as a
potential solution.

draft-rosenberg-sip-ua-loose-route-02 clearly states that History-Info
functionally can be used to solve the problem described in that
document.  However, Jonathan's objective is to solve a fundamental
problem of not distinguishing routing versus re-targeting (read section
5).  This document would actually change the content of the History-Info
headers for the same requests, just as it's already identified in RFC
4244 that if you have loose routing in general, that the information is
different in History-Info. 

The document  draft-holmberg-sip-target-uri-delivery-01.txt  doesn't do
anything to change fundamental SIP processing. It just adds another
header that contains information that would already be contained in
History-Info. History-info provides a complete history of the processing
of a request, with the indexing provided by the entries and the reasons,
you know exactly why a request was either "retargetted" or "re-routed".
The examples in the appendix would apply to the use cases you are
attempting to solve as described in Jonathan's document. 

Mary. 
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---

From: "Francois Audet" <[email-masked]>
Date: Thu, 13 Mar 2008 12:43:21 -0500

Thanks Mary.
 
By the way, RFC 4458 (voicemail URI) describes in the last paragraph of section 4 how History-Info solves the problem of URI parameters being dropped as a result of routing or retargeting.
 
Therefore, if we chose the History-Info route for this problem, RFC 4458 would magically be forward compatible.

________________________________

	From: [email-masked] [mailto:[email-masked]] On Behalf Of Barnes, Mary (RICH2:AR00)
	Sent: Thursday, March 13, 2008 08:34
	To: [email-masked]
	Subject: [Sip] History-Info: UA loose route versus Target header

	Per my comments at the microphone, here's my assessment of the difference between the two documents as they apply to History-Info as a potential solution.

	draft-rosenberg-sip-ua-loose-route-02 clearly states that History-Info functionally can be used to solve the problem described in that document.  However, Jonathan's objective is to solve a fundamental problem of not distinguishing routing versus re-targeting (read section 5).  This document would actually change the content of the History-Info headers for the same requests, just as it's already identified in RFC 4244 that if you have loose routing in general, that the information is different in History-Info. 

	The document  draft-holmberg-sip-target-uri-delivery-01.txt  doesn't do anything to change fundamental SIP processing. It just adds another header that contains information that would already be contained in History-Info. History-info provides a complete history of the processing of a request, with the indexing provided by the entries and the reasons, you know exactly why a request was either "retargetted" or "re-routed".   The examples in the appendix would apply to the use cases you are attempting to solve as described in Jonathan's document. 

	Mary.

---

From: "Elwell, John" <[email-masked]>
Date: Thu, 13 Mar 2008 18:30:27 +0000

One problem identified with Target-Id was that a proxy that retargets
and doesn't support Target-Id might just forward an existing Target-Id
rather than remove it. I think history-info has a similar property,
i.e., the last history entry will not necessarily reflect the most
recent target. Would anybody care to comment on this?
 
John

	From: [email-masked] [mailto:[email-masked]] On
Behalf Of Mary Barnes
	Sent: 13 March 2008 15:34
	To: [email-masked]
	Subject: [Sip] History-Info: UA loose route versus Target header

	draft-rosenberg-sip-ua-loose-route-02 clearly states that
History-Info functionally can be used to solve the problem described in
that document.  However, Jonathan's objective is to solve a fundamental
problem of not distinguishing routing versus re-targeting (read section
5).  This document would actually change the content of the History-Info
headers for the same requests, just as it's already identified in RFC
4244 that if you have loose routing in general, that the information is
different in History-Info. 

	The document  draft-holmberg-sip-target-uri-delivery-01.txt
doesn't do anything to change fundamental SIP processing. It just adds
another header that contains information that would already be contained
in History-Info. History-info provides a complete history of the
processing of a request, with the indexing provided by the entries and
the reasons, you know exactly why a request was either "retargetted" or
"re-routed".   The examples in the appendix would apply to the use cases
you are attempting to solve as described in Jonathan's document. 

	Mary.

---

From: "Francois Audet" <[email-masked]>
Date: Thu, 13 Mar 2008 14:07:03 -0500

Well, yes, of course.  That is not a solvable problem.

	From: [email-masked] [mailto:[email-masked]] On Behalf Of Elwell, John
	Sent: Thursday, March 13, 2008 11:30
	To: Barnes, Mary (RICH2:AR00); [email-masked]
	Subject: Re: [Sip] History-Info: UA loose route versus Target header

	One problem identified with Target-Id was that a proxy that retargets and doesn't support Target-Id might just forward an existing Target-Id rather than remove it. I think history-info has a similar property, i.e., the last history entry will not necessarily reflect the most recent target. Would anybody care to comment on this?
	 
	John

		From: [email-masked] [mailto:[email-masked]] On Behalf Of Mary Barnes
		Sent: 13 March 2008 15:34
		To: [email-masked]
		Subject: [Sip] History-Info: UA loose route versus Target header

		Mary.

---

From: "Hans Erik van Elburg" <[email-masked]>
Date: Thu, 13 Mar 2008 20:48:12 +0100

Hi Mary,
 
I dont think that the objective should be to change the fundamental
nature of SIP processing for no good reason. It will break things.
 
The probem with the History-Info is that one can not distinguish
reroutes from retargets and hence it can not be used for this. If you
disagree with that could you address why you think this is not the case?
 
/Hans Erik

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Mary Barnes
Sent: Thursday, March 13, 2008 11:34 AM
To: [email-masked]
Subject: [Sip] History-Info: UA loose route versus Target header

Mary.

---

From: "Mary Barnes" <[email-masked]>
Date: Thu, 13 Mar 2008 16:43:04 -0500

You will know whether or not  the last entity that retargeted or routed
the request to the terminator added an HI entry, since the concept of
the old and new is captured - i.e., the entity receiving the request
determines whether the last HI entry matches the request-URI in the
request.  It was a fundamental requirement (CONTENT-Req) that both the
new URI and the one that was retargetted are captured.  In that case,
you can know that the previous HI entry was the request-URI for the
previous hop.   
 
So, in that respect History-Info is better than the Target-ID.  I also
think that if you do the detailed flows for your scenarios, including
the complete HI, you can see the pattern for determining the right entry
to use due to the indices and reasons included in the entries.
Basically, you're moving the logic to the endpoint that receives the
request rather than having the proxies do extra work along the way to
determine what the Target-ID should be.
 
Mary. 

From: Audet, Francois (SC100:3055) 
Sent: Thursday, March 13, 2008 2:07 PM
To: Elwell, John; Barnes, Mary (RICH2:AR00); [email-masked]
Subject: RE: [Sip] History-Info: UA loose route versus Target header

	From: [email-masked] [mailto:[email-masked]] On
Behalf Of Elwell, John
	Sent: Thursday, March 13, 2008 11:30
	To: Barnes, Mary (RICH2:AR00); [email-masked]
	Subject: Re: [Sip] History-Info: UA loose route versus Target
header

	One problem identified with Target-Id was that a proxy that
retargets and doesn't support Target-Id might just forward an existing
Target-Id rather than remove it. I think history-info has a similar
property, i.e., the last history entry will not necessarily reflect the
most recent target. Would anybody care to comment on this?
	 
	John

		From: [email-masked] [mailto:[email-masked]]
On Behalf Of Mary Barnes
		Sent: 13 March 2008 15:34
		To: [email-masked]
		Subject: [Sip] History-Info: UA loose route versus
Target header

		Per my comments at the microphone, here's my assessment
of the difference between the two documents as they apply to
History-Info as a potential solution.

		draft-rosenberg-sip-ua-loose-route-02 clearly states
that History-Info functionally can be used to solve the problem
described in that document.  However, Jonathan's objective is to solve a
fundamental problem of not distinguishing routing versus re-targeting
(read section 5).  This document would actually change the content of
the History-Info headers for the same requests, just as it's already
identified in RFC 4244 that if you have loose routing in general, that
the information is different in History-Info. 

		The document
draft-holmberg-sip-target-uri-delivery-01.txt  doesn't do anything to
change fundamental SIP processing. It just adds another header that
contains information that would already be contained in History-Info.
History-info provides a complete history of the processing of a request,
with the indexing provided by the entries and the reasons, you know
exactly why a request was either "retargetted" or "re-routed".   The
examples in the appendix would apply to the use cases you are attempting
to solve as described in Jonathan's document. 

		Mary.

---

From: "Mary Barnes" <[email-masked]>
Date: Thu, 13 Mar 2008 16:46:40 -0500

You can tell retargets versus rerouting due to combination of the
reasons in the various responses and the indices.  With the indices you
can get a trace (in the form of a tree structure due to the nesting of
the indices) that shows the entire history of a request. 
 
Mary. 

From: Hans Erik van Elburg [mailto:[email-masked]] 
Sent: Thursday, March 13, 2008 2:48 PM
To: Barnes, Mary (RICH2:AR00); [email-masked]
Subject: RE: [Sip] History-Info: UA loose route versus Target header

Hi Mary,

 
/Hans Erik

Mary.

---

From: "Hans Erik van Elburg" <[email-masked]>
Date: Mon, 17 Mar 2008 11:39:46 +0100

A reroute and a retarget (using the definitions of the ua-loose-route
draft) may both be caused by some local policy deployed on a proxy, it
is not clear how they should be distinguished by reason values. And it
is certainly nowhere defined what different reasons would be applicable
in these cases.
 
To complicate things further to RFC4244 any rewrite of the Request URI
is a retarget, not so in the more subtle definitions used in the
ua-loose-route draft which distinguishes retargets from reroutes.
 
Therefore I insist that History-Info as it is today, does not cover
this.
 
/Hans Erik

From: Mary Barnes [mailto:[email-masked]] 
Sent: Thursday, March 13, 2008 10:47 PM
To: Hans Erik van Elburg; [email-masked]
Subject: RE: [Sip] History-Info: UA loose route versus Target header

Mary. 

Hi Mary,

 
/Hans Erik

Mary.

---

From: "Hans Erik van Elburg" <[email-masked]>
Date: Mon, 17 Mar 2008 12:31:03 +0100

When an entity receives a History-Info with the last entry not being
equal to the Request URI, the only thing that it can infer from that, is
that the one or more previous traversed entities do not support the
History-Info. I do not see how that helps in determining what the
current target is.
 
/Hans Erik

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Mary Barnes
Sent: Thursday, March 13, 2008 10:43 PM
To: Francois Audet; Elwell, John; [email-masked]
Subject: Re: [Sip] History-Info: UA loose route versus Target header

 
Mary. 

	 
	John

		The document

		Mary.

---

From: "Mary Barnes" <[email-masked]>
Date: Mon, 17 Mar 2008 09:01:01 -0500

The reason every rewrite of a Request URI is a retarget is because the
base SIP spec did not distinguish reroute from retargeting, which is the
gist of Jonathan's proposal.  There are explicit reasons associated with
some of the retargets (e.g., 3xx redirections), but I would agree that
isn't always the case. But, I still contend that you can tell from the
structure of the combination of routes/retargets what was the intended
target, especially considering the use cases given.   It does require
that the entity that does the retargeting to capture the History-Info,
but the "Target" header solution has the same requirement.  
 
If the concern is the processing to sort through the HI entries (the
reason that Jonathan's draft suggests HI is not a good solution), then
you could add a "retarget" (and "reroute") tags to the appropriate HI
entry, since History-Info was designed to be extensible. 
 
Mary. 

From: Hans Erik van Elburg [mailto:[email-masked]] 
Sent: Monday, March 17, 2008 5:40 AM
To: Barnes, Mary (RICH2:AR00); [email-masked]
Subject: RE: [Sip] History-Info: UA loose route versus Target header

 
 
/Hans Erik

 
Mary. 

Hi Mary,

 
/Hans Erik

Mary.

---

From: "Francois Audet" <[email-masked]>
Date: Mon, 17 Mar 2008 11:16:54 -0500

Right. I think adding something indicating it's a reroute for the last hop would be useful.

	From: [email-masked] [mailto:[email-masked]] On Behalf Of Barnes, Mary (RICH2:AR00)
	Sent: Monday, March 17, 2008 07:01
	To: Hans Erik van Elburg; [email-masked]
	Subject: Re: [Sip] History-Info: UA loose route versus Target header

	The reason every rewrite of a Request URI is a retarget is because the base SIP spec did not distinguish reroute from retargeting, which is the gist of Jonathan's proposal.  There are explicit reasons associated with some of the retargets (e.g., 3xx redirections), but I would agree that isn't always the case. But, I still contend that you can tell from the structure of the combination of routes/retargets what was the intended target, especially considering the use cases given.   It does require that the entity that does the retargeting to capture the History-Info, but the "Target" header solution has the same requirement.  
	 
	If the concern is the processing to sort through the HI entries (the reason that Jonathan's draft suggests HI is not a good solution), then you could add a "retarget" (and "reroute") tags to the appropriate HI entry, since History-Info was designed to be extensible. 
	 
	Mary. 

	A reroute and a retarget (using the definitions of the ua-loose-route draft) may both be caused by some local policy deployed on a proxy, it is not clear how they should be distinguished by reason values. And it is certainly nowhere defined what different reasons would be applicable in these cases.
	 
	To complicate things further to RFC4244 any rewrite of the Request URI is a retarget, not so in the more subtle definitions used in the ua-loose-route draft which distinguishes retargets from reroutes.
	 
	Therefore I insist that History-Info as it is today, does not cover this.
	 
	/Hans Erik

	You can tell retargets versus rerouting due to combination of the reasons in the various responses and the indices.  With the indices you can get a trace (in the form of a tree structure due to the nesting of the indices) that shows the entire history of a request. 
	 
	Mary. 

	Hi Mary,
	 
	I dont think that the objective should be to change the fundamental nature of SIP processing for no good reason. It will break things.
	 
	The probem with the History-Info is that one can not distinguish reroutes from retargets and hence it can not be used for this. If you disagree with that could you address why you think this is not the case?
	 
	/Hans Erik

	Mary.

---

From: "Hans Erik van Elburg" <[email-masked]>
Date: Mon, 17 Mar 2008 22:50:58 +0100

Exactly the sort through the HI entries approach is not well specified
and therfore the outcome is not predictable.
 
/Hans Erik

From: Mary Barnes [mailto:[email-masked]] 
Sent: Monday, March 17, 2008 3:01 PM
To: Hans Erik van Elburg; [email-masked]
Subject: RE: [Sip] History-Info: UA loose route versus Target header

 
Mary. 

 

/Hans Erik

 
Mary. 

Hi Mary,

 
/Hans Erik

Mary.