[apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13

ht@inf.ed.ac.uk (Henry S. Thompson) Mon, 16 May 2011 09:04 UTC

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To: apps-discuss@ietf.org, Mary Barnes <mary.ietf.barnes@gmail.com>, Chris Boulton <chris@ns-technologies.com>, Simon Pietro Romano <spromano@unina.it>, Henning Schulzrinne <hgs+xcon@cs.columbia.edu>, Alan Johnston <alan.b.johnston@gmail.com>, Richard Barnes <barnes@bbn.com>, iesg@ietf.org
From: ht@inf.ed.ac.uk (Henry S. Thompson)
Date: Mon, 16 May 2011 10:04:29 +0100
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Subject: [apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13
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I have been selected as the Applications Area Review Team reviewer for
this draft (for background on apps-review, please see

Please resolve these comments along with any other Last Call comments
you may receive. Please wait for direction from your document shepherd
or AD before posting a new version of the draft.

Document: draft-ietf-xcon-ccmp-13

Title: Centralized Conferencing Manipulation Protocol

Reviewer: Henry S. Thompson

Review Date: 2011-05-13

Summary: This draft is almost ready for publication as a Proposed
Standard but has a few issues that should be fixed before publication

Major Issues: 

4.2 Data Management

1) The approach to detecting competing updates and their consequences
   specified here seems unnecessarily complex.  Was the alternative of
   including version numbers in _update_ messages (so that the server
   could reject any update whose target version had been superseded)
   considered and rejected?  If so, perhaps a brief explanation of why
   it was rejected might be helful at this point.

2) In a related point, the statement at the end of this section that
   "a client subscribed to . . . notifications . . . will always have
   the most up-to-date version" is clearly false, in-so-far as it
   implies that such a client is guaranteed success for any update, as
   there is clearly a race condition here.

4.3 Data Model Compliance

1) Again this approach seems unnecessarily complex -- why does the
   data model have to constrain the initiation of a conference in this
   way.  why not simply have messages which request new conference or
   new user IDs?

2) I'm also confused by the fact that _elements_ described here as
   "mandatory" are not required by the schema.  Specifically in 5.1 we
   will see that the 'confUserID' and 'confObjID' elements, which
   correspond precisely to XCON-USERID and XCON-URI which are
   described here as mandatory, appear in message type definitions as
   minOccurs="0", i.e. as optional.  If they are optional, why is the
   above gensym complexity needed?  If they are not optional, why
   doesn't the schema say so?

3) It is unusual to refer to aspects of a data model with words such
   as 'element' and 'attribute', which are better reserved for use
   with respect to _XML serializations_ of data model instances.  Ah,
   I see by looking at draft-ietf-xcon-common-data-model that the XCON
   data model is defined as an XML document.  It's undoubtedly too
   late to do anything about that, but confounding data models and XML
   serializations is usually considered to be a mistake. . .

11. XML Schema

An http URI should be provided where this schema document can be found
on its own, and an update policy for it (or, preferably, _two_ URIs,
one for exactly this schema document, and one which will be updated if
this document is revised or superseded).  (Likewise for DataModel.xsd
and rfc4575.xsd.)

12.5 CCMP Protocol Registry

Why are these registries needed?  No role is specified for them
anywhere in the body of the document. Registries are not free, and if
all the information in the registry is also in the published schemas
it's not at all clear what purpose they will serve.

Minor Issues: 

6.2. Alice gets detailed information about a specific blueprint

The blueprintResponse message is not schema-valid per ccmp.xsd.  On
lines 32 and 33 of the example read
The problem really lies in DataModel.xsd -- whereas (correctly)
ccmp.xsd uses xs:token as the base type for enumerated types,
DataModel.xsd (in draft-ietf-xcon-common-data-model) uses xs:string,
and the string value of the above element is "confirm
                      ", which is not one of the allowed values.  The
example should be corrected, or, for preference, the schema in
draft-ietf-xcon-common-data-model should be changed to use xs:token as
the base type for join-handling-type and all other enumerated types.

A similar problem occurs in the response in 6.3

6.9 Alice exploits a CCMP server extension

For compatibility with the actual response given, the extension schema
document should have a target namespace, as follows:

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

     <xs:element name="confSummary" type="conf-summary-type"/>

     <xs:complexType name="conf-summary-type">
	 <xs:element name="title" type="xs:string"/>
	 <xs:element name="status" type="xs:string"/>
	 <xs:element name="public" type="xs:boolean"/>
	 <xs:element name="media" type="xs:string"/>


Or, better, the example _and_ the schema should be changed to read as

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <ccmp:ccmpResponse xmlns:info="urn:ietf:params:xml:ns:conference-info"
      <ccmpResponse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

		 <title> Alice's conference </title>
		 <status> active </status>
		 <public> true </public>
		 <media> audio </media>

    <?xml version="1.0" encoding="UTF-8"?>
    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

      <xs:element name="confSummary" type="conf-summary-type"/>

      <xs:complexType name="conf-summary-type">
	  <xs:element name="title" type="xs:string"/>
	  <xs:element name="status" type="xs:string"/>
	  <xs:element name="public" type="xs:boolean"/>
	  <xs:element name="media" type="xs:string"/>


Otherwise I've checked all the schemas for conformance and the
examples for schema-validity.

12.2 XML Schema Registration

Should include pointers to the RFCs which include the text of the
schema documents named as "DataModel.xsd" and "rfc4575.xsd" in the
schema docuemnt given in section 11.

12.3 Media Type Registration

It seems unlikely that the proposed extension of 'ccmpxml' will see
much use---4 characters seems to be the practical limit for

Nits: One more proofreading pass over the first three sections would
be a good idea. . .

       Henry S. Thompson, School of Informatics, University of Edinburgh
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
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