Subject: [Fwd: Re: [Sip] Comments on draft-ietf-sip-multiple-refer-01.txt]

From: Neil Hampton <[email-masked]>
Date: Fri, 16 Feb 2007 13:26:32 +1300

Hi,

I was hoping to use building blocks too - since we already have and 
implementation that will turn a Refer-To (or whatever header) into an 
INVITE (or other) request it would have been very easy to extend this to 
act on multiple values. According to this draft, however, we must now 
support two different ways of specifying a destination.  While it is no 
great deal to add an XML parser to resource rich devices (e.g. a PC) it 
can have a significant impact on resource limited/restricted devices.

>From your response, I am not sure that I understand how XML documents 
for URI lists can be used for non-REFER methods.  You mention its use 
for the INVITE and MESSAGE methods - surely these already have bodies 
(i.e. SDP and the message).
What is wrong with re-using the method used by, for example, a '300 
Multiple Choices' response which specifies a list of URIs in Contact 
headers?
You also mention the ability to add attributes as an advantage of XML - 
this does also exists within the SIP format in the form of parameters.  
Is this not sufficient?

Normally when looking at a protocol I would expect the request for 
multiple elements to be an extension of the request for one element.
>From a reverse engineering case, after seeing a REFER message with an 
XML body containing a list URIs I would expect the case for a REFER with 
one element to be the same except there would only be one element in the 
XML body.  This is not the case (although it would probably work on 
devices that accept this extension).

I was expecting something simpler, along the lines of a SIP extension 
that implied multiple Refer-To headers are allowed in a REFER message.

Personally I think that XML is a bit of a bandwagon that gets used as a 
'solution for everyone' format (bit like ADA ;)).  It has its place for 
structured data, documents and so on; but I don't think it should be 
mixed with other protocols in this way.  I think that SIP should be used 
for the communications and getting the data to the right place and the 
XML should be left for document exchange, user directories, etc.

Regards,
Neil Hampton.
Hampton Software Ltd.
Tel: +64 9 974 3601
Mobile: +64 2102 344909
http://www.hamptonsoftware.co.uk

Hampton Software Limited is a company incorporated in England and Wales (Company Number 5563994)
and has its registered office at Hatherley House, Bisley Green, Bisley, Surrey.  GU24 9EW.

Miguel Garcia wrote:
> Hi Neil:
>
> The decision of using an XML document to convey the list of recipients 
> was taking long time ago. At that time, we wanted to re-use as much as 
> possible existing available building blocks, and XML documents for 
> URI-lists were already there. Especially, the first method that was 
> adopted to use a URI-list was INVITE, and there is no Refer-To header 
> in an INVITE request, so the Refer-To wasn't an option. Additionally, 
> we can reuse the same list format for other non-REFER URI-list 
> methods, such as MESSAGE, INVITE, and SUBSCRIBE. These methods do not 
> contain a Refer-To header, as I said.
>
> Using XML URI-lists has other advantages, such as the possibility to 
> add attributes, for example to qualify a recipient as a copied 
> (similar to e-mail cc:).
>
> The kind of lists that we are managing are fairly simple, so you don't 
> really need to build a general XML parser, if you don't want to do it, 
> but in any case, there are a few open source XML parsers out there. 
> Whether we like it or not, XML is more and more present in our SIPpish 
> lifes.
>
> /Miguel
>
>
>
> Neil Hampton wrote:
>

-- 
Regards,
Neil Hampton.
Hampton Software Ltd.
Tel: +64 9 974 3601
Mobile: +64 2102 344909
http://www.hamptonsoftware.co.uk

Hampton Software Limited is a company incorporated in England and Wales (Company Number 5563994)
and has its registered office at Hatherley House, Bisley Green, Bisley, Surrey.  GU24 9EW.

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