Re: [MMUSIC] [Technical Errata Reported] RFC4566 (3278)

"Stach, Thomas" <thomas.stach@siemens-enterprise.com> Fri, 06 July 2012 08:00 UTC

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From: "Stach, Thomas" <thomas.stach@siemens-enterprise.com>
To: "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] [Technical Errata Reported] RFC4566 (3278)
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Date: Fri, 06 Jul 2012 08:01:12 +0000
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Subject: Re: [MMUSIC] [Technical Errata Reported] RFC4566 (3278)
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All,

I think this errata should be rejected.

The text on page 9 is pretty clear and I don't see a conflict with the ABNF.
 
Under "Session description" it is explicitly stated that you can have zero or more media descriptions (as well as time descriptions)
Further down under "Media description, if present" it is elaborated what a media description includes. 
It must at least include exactly one m-line. The a,b,k,i,c-lines are optional.
Adding the asterisk as proposed would remove this subtlety.
The same technique is used for "Time description". The t-line is mandatory, the r-lines are optional. 

BTW: Being able to provide zero media descriptions is crucial for certain implementations. An example is tunneling QSIG in SIP.

Regards
Thomas  

> -----Ursprüngliche Nachricht-----
> Von: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] 
> Im Auftrag von RFC Errata System
> Gesendet: Dienstag, 03. Juli 2012 20:01
> An: M.Handley@cs.ucl.ac.uk; van@packetdesign.com; 
> csp@csperkins.org; gonzalo.camarillo@ericsson.com; 
> rjsparks@nostrum.com; fandreas@cisco.com; miguel.a.garcia@ericsson.com
> Cc: mmusic@ietf.org; rfc-editor@rfc-editor.org
> Betreff: [MMUSIC] [Technical Errata Reported] RFC4566 (3278)
> 
> 
> The following errata report has been submitted for RFC4566,
> "SDP: Session Description Protocol".
> 
> --------------------------------------
> You may review the report below and at:
> http://www.rfc-editor.org/errata_search.php?rfc=4566&eid=3278
> 
> --------------------------------------
> Type: Technical
> Reported by: Riccardo Bernardini <riccardo.bernardini@uniud.it>
> 
> Section: 5
> 
> Original Text
> -------------
> At page 9:
> 
> 
>       Media description, if present
>          m=  (media name and transport address)
> 
> Corrected Text
> --------------
> 
>       Media description, if present
>          m=* (media name and transport address)
> 
> 
> 
> Notes
> -----
> A '*' is added making "m=" lines optional
> 
> Rationale: 
> The description about media lines in section 5, page 9 is 
> conflicting with the ABNF syntax of media-description in 
> Section 9, page 40
> 
> media-descriptions =  *( media-field
>                          information-field
>                          *connection-field
>                          bandwidth-fields
>                          key-field
>                          attribute-fields )
> 
> According to the ABNF grammar, an SDP description can have 
> zero "m=" lines, but according to the description at page 9, 
> at least one line must be present.  Note that the conflict 
> could be solved also by replacing the media-descriptions 
> definition with 
> 
>    media-descriptions =  1*( media-field ... )
> 
> but at page 8 (still Section 5) it is said
> 
>    An SDP session description consists of a session-level section
>    followed by zero or more media-level sections. ...
>                ^^^^^^^^^^^^^^^^^^^^^^^^
> 
> so, I guess that the ABNF grammar is correct.
> 
> Instructions:
> -------------
> This errata is currently posted as "Reported". If necessary, please
> use "Reply All" to discuss whether it should be verified or
> rejected. When a decision is reached, the verifying party (IESG)
> can log in to change the status and edit the report, if necessary. 
> 
> --------------------------------------
> RFC4566 (draft-ietf-mmusic-sdp-new-26)
> --------------------------------------
> Title               : SDP: Session Description Protocol
> Publication Date    : July 2006
> Author(s)           : M. Handley, V. Jacobson, C. Perkins
> Category            : PROPOSED STANDARD
> Source              : Multiparty Multimedia Session Control
> Area                : Real-time Applications and Infrastructure
> Stream              : IETF
> Verifying Party     : IESG
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