Re: Definition of a=rid in draft-ietf-mmusic-rid-09 (was WGLC on draft-ietf-mmusic-sdp-simulcast-07)

Dale,

The "a=rid" line syntax you are quoting from -mmusic-rid-09 below is not the formal definition and it is therefore not meant to interpret formally, specifically not the "..." at the end, but only meant to provide an example. The text in -mmusic-rid-09 just above that quoted line also refers to section 10 for the formal definition. ISTM that the formal definition is entirely correct, not lacking the ";" between rid parameters that formal interpretation of "..." would imply:

   rid-syntax        = "a=rid:" rid-id SP rid-dir
                       [ rid-pt-param-list / rid-param-list ]

   rid-id            = 1*(alpha-numeric / "-" / "_")

   alpha-numeric     = < as defined in {{RFC4566}} >

   rid-dir           = "send" / "recv"

   rid-pt-param-list = SP rid-fmt-list *(";" rid-param)

   rid-param-list    = SP rid-param *(";" rid-param)

   rid-fmt-list      = "pt=" fmt *( "," fmt )

   fmt               = < as defined in {{RFC4566}} >

   rid-param         = rid-width-param
                       / rid-height-param
                       / rid-fps-param
                       / rid-fs-param
                       / rid-br-param
                       / rid-pps-param
                       / rid-bpp-param
                       / rid-depend-param
                       / rid-param-other

<definition continues with defining the individual rid-param components>

It is probably unfortunate that the quoted "a=rid" line is not 100% compliant ABNF, but I don't see the point in having (different) formal definitions in two places in the document and the text already says that this is not the formal definition.

/Bo
(as individual)


> -----Original Message-----
> From: mmusic [mailto:[email protected]] On Behalf Of Dale R. Worley
> Sent: den 6 mars 2017 20:50
> To: Paul Kyzivat <[email protected]>
> Cc: [email protected]
> Subject: [MMUSIC] Definition of a=rid in draft-ietf-mmusic-rid-09 (was WGLC on draft-ietf-mmusic-sdp-simulcast-07)
> 
> Paul Kyzivat <[email protected]> writes:
> > On 3/3/17 10:56 AM, Dale R. Worley wrote:
> >> Inaki Baz Castillo <[email protected]> writes:
> >>>> but according to
> >>>> https://tools.ietf.org/html/draft-ietf-mmusic-rid-09
> >>>> it seems that "direction" (send/recv) should be placed *before*
> >>>> "pt=xx":
> >>>>
> >>>> a=rid:<rid-id> <direction> [pt=<fmt-list>;]<restriction>=<value>...
> >>>
> >>> In fact, pt=xx seems to be yet another "param".
> >>
> >> That purported BNF is really bizarre, since it generates the clearly
> >> incorrect form:
> >
> > IIUC you are commenting on the ABNF in draft-ietf-mmusic-rid-08, not
> > in draft-ietf-mmusic-sdp-simulcast-07, right?
> >
> >>    a=rid:<rid-id> <direction>
> >> <restriction>=<value><restriction>=<value>
> >
> > I'm not seeing how the ABNF generates that.
> 
> What I'm commenting on is this line way back in the innermost quoted message
> 
> >>>> a=rid:<rid-id> <direction> [pt=<fmt-list>;]<restriction>=<value>...
> 
> which was in turn quoted from draft-ietf-mmusic-rid-09.
> 
> In BNF-like notations, "..." means "repetition of the preceding thing", which I took to mean repetition of
> "<restriction>=<value>".  Although that's probably not the correct interpretation, and rather it means repetition of
> "<value>".
> 
> >> A correct description is:
> >>
> >>    a=rid:<rid-id> <direction> ( pt=<fmt-list> | <restriction>=<value>
> >> ) *( ; <restriction>=<value> )
> >
> > ISTM the ABNF in the draft is equivalent to what you have written.
> > (Though yours is clearer.)
> 
> What I don't see is why mmusic-rid-09 requires the pt restriction to be in first position.  I'm not read into it, but it seems
> that there's no semantic reason why it must be first, and it makes the grammar messier to force it to be so.  Without that
> restriction, you could just say
> 
> >>    a=rid:<rid-id> <direction> <restriction>=<value> *( ;
> >> <restriction>=<value> )
> 
> and allow pt to be one of the <restriction>s.
> 
> Dale
> 
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