Subject: [sipcore] Summary: number of location headers

From: Adam Roach - SIPCORE Chair <[email-masked]>
Date: Tue, 09 Nov 2010 17:10:20 +0800

[as chair]

I just wanted to summarize where it looks like the discussion ended up 
on whether we constrain the number of location header fields in a SIP 
message. From my review of the discussion, I believe that four people 
have weighed in on the topic to voice support for an arbitrary number of 
location headers (albeit with a implementation warning that doing so is 
not advisable):

Martin Thompson: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03576.html
Richard Barnes: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03580.html
Keith Drage: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03600.html
Hannu Hietalahti: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03619.html

And two people have agreed to go along with that direction, with 
expressed reservations:

Jon Peterson: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03601.html
James Polk: 
http://www.ietf.org/mail-archive/web/sipcore/current/msg03603.html

If any other working group participants have comments on this topic, 
they are encouraged to make them quickly. Lacking any further input, the 
authors will be instructed to revise the document to allow an arbitrary 
number of location header fields, with an accompanying warning that 
doing so is not recommended.

/a

---

From: "Elwell, John" <[email-masked]>
Date: Wed, 10 Nov 2010 02:46:46 +0100

I think we have to make provision for >1, and limiting it to 2 probably doesn't make sense. However, the warnings must include the fact that anyone inserting an additional location and then getting back a 424 has no way of knowing whether the 424 applies to the location it inserted or a location already present.

John 

> -----Original Message-----
> From: [email-masked] 
> [mailto:[email-masked]] On Behalf Of Adam Roach - 
> SIPCORE Chair
> Sent: 09 November 2010 09:10
> To: SIPCORE (Session Initiation Protocol Core) WG
> Subject: [sipcore] Summary: number of location headers
> 
> [as chair]
> 
> _______________________________________________
> sipcore mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/sipcore
>

---

From: "Thomson, Martin" <[email-masked]>
Date: Wed, 10 Nov 2010 09:53:09 +0800

That's sensible.

On 2010-11-10 at 09:46:46, Elwell, John wrote:
> I think we have to make provision for >1, and limiting it to 2 probably
> doesn't make sense. However, the warnings must include the fact that
> anyone inserting an additional location and then getting back a 424 has
> no way of knowing whether the 424 applies to the location it inserted
> or a location already present.
> 
> John
>

---

From: <[email-masked]>
Date: Thu, 11 Nov 2010 06:45:57 +0100

Thanks for summarising, Adam,

being one of those requesting this change I of course support it, but could we please also re-word the warning against adding multiple locations from "SHOULD NOT" to giving a warning that adding more location objects does not guarantee better accuracy and any possible conflict resolution is left for the receiver of this information.

The issue is real and I am not arguing to remove this warning. But in case of emergency calls just strongly recommending against multiple location objects with "SHOULD NOT" does not help much if both the terminal and the network *have to* insert their best understanding of the user's location.

BR,
Hannu Hietalahti
3GPP TSG CT Chairman
tel: +358 40 5021724

>[mailto:[email-masked]] On Behalf Of ext Adam Roach 
>- SIPCORE Chair
>Sent: 09 November, 2010 11:10

---

From: "James M. Polk" <[email-masked]>
Date: Thu, 11 Nov 2010 00:15:02 -0600

Hannu

One aspect you do not mention below is how erroring is handled with 
multiple locations in the same SIP request. As the doc stands today, 
there is no consideration for who receives the 424 as to which 
location was in error. If there is only 1 location, this is simple to 
correlate.

I am sympathetic to the emergency services case, and I'm hesitant to 
call that one case out as an exception because in the future there 
might be an equally valid case that hasn't been called out - then 
where are we (i.e., is the RFC then accurate?).

Therefore, I think the emergency case can be an example of why 
"SHOULD NOT" doesn't apply, but that it is justified in an emergency 
document, and not here in the general purpose document (i.e., this is 
better suited IMO for ECRIT phonebcp or ECRIT framework documents).

With that logic, respectfully, I think SHOULD NOT is appropriate here.

James

At 11:45 PM 11/10/2010, [email-masked] wrote:
>being one of those requesting this change I of course support it, 
>but could we please also re-word the warning against adding multiple 
>locations from "SHOULD NOT" to giving a warning that adding more 
>location objects does not guarantee better accuracy and any possible 
>conflict resolution is left for the receiver of this information.
>
>The issue is real and I am not arguing to remove this warning. But 
>in case of emergency calls just strongly recommending against 
>multiple location objects with "SHOULD NOT" does not help much if 
>both the terminal and the network *have to* insert their best 
>understanding of the user's location.
>
>BR,
>Hannu Hietalahti
>3GPP TSG CT Chairman
>tel: +358 40 5021724
>
>

---

From: <[email-masked]>
Date: Thu, 11 Nov 2010 09:51:04 +0100

Thanks James,

I agree. Jon already gave me his explanation which was pretty similar to yours and therefore I am willing to withdraw my request to avoid the "SHOULD NOT". While saying SHOULD NOT, we might also want to give the reason to that strong recommendation, though?

We know at least one case where it will be mandatory for the terminal and the network to insert the user location. I hope the problem with correlating 424 reject to any of the multiple location objects does not stop us keeping the option of multiple location objects.

BR,
Hannu Hietalahti
3GPP TSG CT Chairman
tel: +358 40 5021724

>From: ext James M. Polk [mailto:[email-masked]] 
>Sent: 11 November, 2010 08:15
>To: Hietalahti Hannu (Nokia-CIC/Oulu); 
>[email-masked]; [email-masked]
>Subject: Re: [sipcore] Summary: number of location headers
>
>Hannu
>