Re: [MMUSIC] RTSP 2.0 SDP issue: Directionality attribute

[Sean Sheedy <[e-mail]>]

This change sounds good to me.  I would recommend changing "In SDP 
provided ..." to "SDP provided ...".

Sean


On 03/14/2013 07:12 PM, Magnus Westerlund wrote:
> WG,
>
> Flemming has found an issue in Section D.1.5. This is that this section
> actually redefined the default behavior of the a=sendrecv, a=recvonly,
> a=sendonly. This is clearly unsuitable and I propose that we change the
> current text:
>
> D.1.5.  Directionality of media stream
>
>     The SDP attributes "a=sendrecv", "a=recvonly" and "a=sendonly"
>     provide instructions about the direction the media streams flow
>     within a session.  When using RTSP the SDP can be delivered to a
>     client using either RTSP DESCRIBE or a number of RTSP external
>     methods, like HTTP, FTP, and email.  Based on this the SDP applies to
>     how the RTSP client will see the complete session.  Thus media
>     streams delivered from the RTSP server to the client, would be given
>     the "a=recvonly" attribute.
>
>     The direction attributes are not commonly used in SDPs for RTSP, but
>     may occur. "a=recvonly" in a SDP provided to the RTSP client MUST
>     indicate that media delivery will only occur in the direction from
>     the RTSP server to the client.  In SDP provided to the RTSP client
>     that lacks any of the directionality attributes (a=recvonly,
>     a=sendonly, a=sendrecv) MUST behave as if the "a=recvonly" attribute
>     was received.  Note that this overrules the normal default rule
>     defined in SDP[RFC4566].  The usage of "a=sendonly" or "a=sendrecv"
>     is not defined, nor is the interpretation of SDP by other entities
>     than the RTSP client.
>
> To instead become:
>
> D.1.5.  Directionality of media stream
>
>     The SDP attributes "a=sendrecv", "a=recvonly" and "a=sendonly"
>     provide instructions about the direction the media streams flow
>     within a session.  When using RTSP the SDP can be delivered to a
>     client using either RTSP DESCRIBE or a number of RTSP external
>     methods, like HTTP, FTP, and email.  Based on this the SDP applies to
>     how the RTSP client will see the complete session.  Thus media
>     streams delivered from the RTSP server to the client, would be given
>     the "a=recvonly" attribute.
>
>     "a=recvonly" in a SDP provided to the RTSP client indicates that
>     media delivery will only occur in the direction from the RTSP server
>     to the client.  In SDP provided to the RTSP client that lacks any of
>     the directionality attributes (a=recvonly, a=sendonly, a=sendrecv)
>     would be interpreated as having a=sendrecv.  At the time of writing
>     there exist no RTSP mode suitable for media traffic in the direction
>     from the RTSP client to the server.  Thus all RTSP SDP SHOULD have
>     a=recvonly attribute when using the PLAY mode defined in this
>     document.  If future modes are defined for media in client to server
>     direction, then usage of a=sendonly, or a=sendrecv may become
>     suitable to indicate intended media directions.  The usage of
>     "a=sendonly" or "a=sendrecv" SHOULD then be well defined.
>
> This means that we expect SDP files for RTSP 2.0 to do contain the
> directionality attribute.
>
> Please provide feedback on this proposal.
>
> Cheers
>
> Magnus Westerlund
>
> ----------------------------------------------------------------------
> Multimedia Technologies, Ericsson Research EAB/TVM
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Sean Sheedy
Staff System Software Engineer, Media and Communications Systems
[e-mail] | 503-495-9454 (Phone)
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