Subject: Re: [MMUSIC] Re: Tool starting mode attributes in SDP

From: Bryan Thale <[email-masked]>
Date: Fri, 26 Jul 2002 15:15:43 -0500

Right.  To do it properly you need something like

"a=toolmode:" ("recvonly" / "sendonly" / "sendrecv") [ 1*SP "inactive" ] CRLF

to group the values of the toolmode attribute together but such a change is not
backward compatible with current implementations.  You could get most of the
benefits of such a change with a combination of a change to the ABNF and a
change to the text describing the recvonly, sendonly, sendrecv, and inactive
attributes.

  1. Change the ABNF to allow only one of recvonly, sendonly, and sendrecv to
     appear in a session or media description and to allow inactive to appear
     only in combination with one of those three.
  2. Change the text to state that the appearance of any of the three at the
     media level overrides any setting at the session level.

Bryan.

--
Bryan Thale
Networks & Infrastructure Research, Motorola Labs
mailto:[email-masked]

Colin Perkins wrote:

> Right, the problem is the override between session and media level. I don't
> think we can express that in the ABNF.
>
> Colin
>

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From: [email-masked]
Date: Mon, 12 Aug 2002 10:28:04 +0300 (EEST)

Hello,

Sorry for the delay.
When I've posted the mail about the four complementary attributes
I was thinking only of changing the text protocol(something like:
'Only one of these attibutes MAY appear at session level and at each
media level').

I think that changing the ABNF syntax may be postponed to the next version
of the SDP protocol (v=3).

Dan Firac,
Software Engineer,
Redline Communications, Romania.

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From: [email-masked]
Date: Mon, 12 Aug 2002 11:52:01 +0300 (EEST)

See below,

> of the SDP protocol (v=3).
Oops,  I meant v=1.

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From: Bryan Thale <[email-masked]>
Date: Mon, 12 Aug 2002 13:35:30 -0500

> > 'Only one of these attibutes MAY appear at session level and at each

Well, you really need to say more than that to adequately clear up that part of the
spec.  For example, what does it mean if the session is set to sendonly and the media
to recvonly?  Each section contains only a single directive, but there is nothing to
explain the relationship between them.  The current mechanism in the spec says the two
attributes are unrelated since they have different attribute names.

> > of the SDP protocol (v=3).

Unlikely since I think XML-based SDPng is meant to replace the current v=0 version of
SDP.

Bryan.