Subject: [AVT] draft-ietf-avt-evrc-07: Marker Bit

From: Randall Gellens <[email-masked]>
Date: Wed, 29 Aug 2001 14:41:21 -0700

Previous versions of the draft specified "this payload type MUST 
never have the marker bit set".  This has been changed to "It is 
recommended that the marker bit should not be set".  The change, as 
I understand it, is to allow a conforming implementation to use the 
marker bit for custom (non-standard) purposes.

I think better wording to achieve this might be "This specification 
does not use the marker bit.  Implementation SHOULD set the marker 
bit to zero when sending, and SHOULD ignore the marker bit when 
receiving."

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
http://www1.ietf.org/mailman/listinfo/avt

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From: Colin Perkins <[email-masked]>
Date: Wed, 29 Aug 2001 21:33:46 -0400

>bit to zero when sending, and SHOULD ignore the marker bit when 

An EVRC sender could feasibly use silence suppression, in which case the M
bit would be required. There was considerable discussion on this subject in
July - it might be worth reviewing the list archive for the rationale for 
the change.

Colin

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From: Stephen Casner <[email-masked]>
Date: Thu, 30 Aug 2001 11:28:21 -0700 (PDT)

On Wed, 29 Aug 2001, Randall Gellens wrote:

> recommended that the marker bit should not be set".

I don't find that text anywhere in draft-ietf-avt-evrc-07.txt.  What
it says about the marker (M) bit is:

   The M bit
   should be set as specified in the applicable RTP profile, for
   example, RFC 1890. Note that RFC 1890 specifies that if the sender
   does not suppress silence (i.e., sends a frame on every 20
   millisecond interval), the M bit will always be zero.

>  The change, as

Definitely not correct.  We try hard to keep the use of the marker bit
consistent.  It would be useful to know what led you to your
misunderstanding.

The reason that was discussed for a recommendation that the bit not be
set is to avoid reducing header compression efficiency.

							-- Steve