Subject: [Sipping] Review of draft-drage-sipping-service-identification-02

From: "Andrew Allen" <[email-masked]>
Date: Sun, 23 Nov 2008 22:19:29 -0500

I have reviewed draft-drage-sipping-service-identification-02

Here are my comments

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Abstract

This URN can be used to identify services within the

   SIP header fields defined in this document, and also within the

   framework defined for caller preferences and callee capabilities in

   to identify usage of both services and applications between end UAs.

Proposed Rephrase

This URN can be used within the SIP header fields defined in this
document 

to identify services, and also within the framework defined for caller 

preferences and callee capabilities to identify usage of both services
and 

applications between end UAs.

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1.	Introduction

   P-Asserted-Service: urn-xxx:exampletelephony.version1

Add

      Note to RFC editor: replace xxx with the assigned 3 numeric digit

      Identifier

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4.2.  The P-Preferred-Service Header

   The P-Preferred-Service header field is used from a user agent to a

   trusted proxy to carry the preferred service of the user sending the

   SIP request that the user wishes to be used for the P-Asserted-

   Service field value that the trusted element will insert.

Proposed rewrite:

   The P-Preferred-Service header field is used by a user agent 

   sending the SIP request to provide a hint to a trusted proxy of the 

   preferred service that the user wishes to be used for the P-Asserted-

   Service field value that the trusted element will insert.

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Propose add RFC 3840

4.3.  Service and Application Definition

   The service and subservice identifiers identify the service as

   described in Section 1.  The URN may also be used to identify a

   service or an application between end users for use within the

   context of RFC 3841 [RFC3841] **and RFC 3840 [RFC3840]**.

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Update Registration Information

4.4 

   Registration Information:  Registration version: 1; registration

      date: 2007-04-21

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5.1.1

There is no text regarding the use of the P-Asserted-Service header by
UACs.

A UAC within the trust domain (such as a Media Gateway or Application
Server) 

Can also include a P-Asserted-Service header. This behavior should also
be 

documented in 5.1.1

Proposed text

A UAC that is within the same trust domain as the proxy it sends a
request

to, (e.g a Media Gateway or Application Server) MAY insert a 

P-Asserted-Service header in a request that creates a dialog, or a
request 

outside of a dialog. This information MUST NOT conflict with other SIP

or SDP information included in the request.  Furthermore, the SIP or

SDP information needed to signal functionality of this service MUST

be present.  

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5.1.2

There is no text regarding the use of the P-Preferred-Service header by
proxies. This needs to be added.

Proposed text

When a proxy receives a request containing a P-Preferred-Service header
the

Proxy MAY use the contents of that header to assist in determining the
service

to be included in a P-Asserted-Service header field, (for instance to
prioritize the

order of comparison of filter criteria for potential services that the
request could

match). The proxy MUST NOT use the contents of the P-Preferred-Service
header to

identify the service without first checking against the capabilities
(e.g.  SDP) contained in 

the request. If the proxy inserts a P-Asserted-Service header in the
request the proxy 

MUST remove the P-Preferred-Service header before forwarding the
request, otherwise the 

Proxy SHOULD include the P-Preferred-Service header when forwarding the
request.

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6 Examples

The text in 6 seems to originate from RFC 3325 and not modified as it
seems to relate to P-Asserted-Identity and not P-Asserted-Service

   In this example, proxy.example.com creates a P-Asserted-Service

   header field from the user identity it discovered from SIP Digest

   authentication, and the list of services appropriate to that user,

   and the services that correspond to the SDP information included in

   the request.  It forwards this information to a trusted proxy which

   forwards it to a trusted gateway.  Note that these examples consist

   of partial SIP messages that illustrate only those headers relevant

   to the authenticated identity problem.

The examples themselves seem identity related too with 407 Proxy
Authorization which is not related to the functionality in this draft.

Since SDP is the most likely means to determine the service I think this
should be shown in the examples

Probably two examples are needed one with P-Preferred-Service and one
without. Also I think we should have in one of the examples the  

proxy stripping the P-Asserted-Service header at the edge of the trust
domain,

Andrew Allen

Manager Standards

Research In Motion Ltd

Office +1 847-793-0861 x20824

BlackBerry Mobile +1 847 809 8636

http://www.rim.com/ <http://www.rim.com/> 

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