Subject: [MMUSIC] SDP 'gpmd' (General Purpose Media Descriptor) attribute

From: Rajesh Kumar <[email-masked]>
Date: Mon, 30 Sep 2002 10:21:34 -0700

Dear MMUSIC colleagues,

A while back, I sent this request for discussion on  the qualification of 
media formats with generic parameters. There have been no comments on the 
issue, or on the referenced internet draft. Please do provide me with your 
feedback.  If approved, this will impact the representation of media 
formats in SDP.

My original email is below...

There is a need for an SDP attribute that allows the qualification of media
formats with generic parameters. By "generic" we mean that these parameters
are not part of the standard  (e.g. MIME) definition of the media format. In
general, the media format may be RTP or non-RTP.

Please take a look at the internet draft,
http://www.ietf.org/internet-drafts/draft-rajeshkumar-mmusic-gpmd-00.txt,
which defines such an attribute. It is meant to replace the internet draft
http://www.ietf.org/internet-drafts/draft-rajeshkumar-mmusic-gfmtp-04.txt.
We withdrew the other internet draft because we changed the parameter name
to gpmd. Although the basics remain unchanged, there older internet draft
had inconsistencies which we have corrected based on feedback from Colin
Perkins.

At the parser level, this attribute is completely optional. However, some
applications might require the use of this attribute and one or more generic
parameters. The format of this attribute is:

      a=gpmd:<format><generic parameter list>

For example,

     m=audio 3456 RTP/AVP 0 15
     a=gpmd:0 vbd=yes

and

      m=application 3456 udp wb
      a=gpmd:wb someParameter=someValue

As an example, we have defined the generic parameter 'vbd' (Voiceband data)
in the internet draft. Unfortunately, we did not limit ourselves to the
semantics of the generic parameter. We specified an implementation. We will
be removing all implementation-specific information from the RFC that might
come out of this internet draft. Thanks, Colin, for pointing out the need
to, in this case, limit the discussion to the semantics of this parameter.

Of course, generic parameters that do not being with the experimental prefix
"X-" will need to be registered with the IANA. We have stated the need for
an IANA registry for this purpose.

A predecessor of this internet draft have been reviewed at the London and
Minneapolis IETF's. Another predecessor of this internet draft was reviewed
on this mailing list and commented on. All comments provided are factored
in.

Please do provide me with your comments!!  I look forward to a cycle of
fruitful discussion on why this attribute should or should not be
standardized in the IETF, and if standardized, what changes might be
appropriate. On a tangential note, please note that the TIA TR.30.1 MoIP
standardization group is actively using this attribute (albeit under its
older name, 'gfmtp', something that needs to be fixed).

Thanks for your attention, help, and suggestions,

Rajesh

---

From: Tom Marshall <[email-masked]>
Date: Mon, 30 Sep 2002 10:45:23 -0700

I question the need for this when the a= line is freefrom and you are free
to put whatever information in whatever format you like.  An application
that does not understand a particular entry/parameter will be no better off
because it cannot use the information, and one that already understands the
current form gains nothing either.

Of course, you are free to use this convention in your SDP.  Our system also
has a convention for passing generic key/value pairs with datatype info.

On Mon, Sep 30, 2002 at 10:21:34AM -0700, Rajesh Kumar wrote:
> Dear MMUSIC colleagues,
> 
> A while back, I sent this request for discussion on  the qualification of media
> formats with generic parameters. There have been no comments on the issue, or
> on the referenced internet draft. Please do provide me with your feedback.  If
> approved, this will impact the representation of media formats in SDP.
> 
> _h_t_t_p_:_/_/_w_w_w_._i_e_t_f_._o_r_g_/_i_n_t_e_r_n_e_t_-_d_r_a_f_t_s_/_d_r_a_f_t_-_r_a_j_e_s_h_k_u_m_a_r_-_m_m_u_s_i_c_-_g_p_m_d_-_0_0_._t_x_t,
> _h_t_t_p_:_/_/_w_w_w_._i_e_t_f_._o_r_g_/_i_n_t_e_r_n_e_t_-_d_r_a_f_t_s_/_d_r_a_f_t_-_r_a_j_e_s_h_k_u_m_a_r_-_m_m_u_s_i_c_-_g_f_m_t_p_-_0_4_._t_x_t.

-- 
Nothing will dispel enthusiasm like a small admission fee.
        -- Kim Hubbard
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