-----Original Message-----
From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org]On Behalf Of
Colin Perkins
Sent: Donnerstag, 5. August 2004 19:09
To: IETF AVT WG
Cc: Magnus Westerlund
Subject: [AVT] RTP and Media Types
Folks,
The working group recently sent the registration for the text/red
media
type <draft-ietf-avt-text-red-05.txt> to the IESG for publication as a
Proposed Standard RFC. The IESG asked for expert review of the draft
by
MIME experts (as is normal for media type registrations). The
reviewers
found a number of problems with the draft, and these issues
potentially
affect all other RTP payload types.
It was noted that the rules for registering media types under the
"text" top level type are stricter than those for audio and video
types. In particular, it is expected that text media types are, to
some
extent,
readable even without the software that interprets them [RFC 2046].
This rule is derived from email client behaviour, where one wants to
pass the message to a dumb pager if there is no better display option,
and have something reasonable happen.
This is clearly not the case for the "text/red" or "text/parityfec"
media types, which are error correcting codes sent over a stream of
unreliable datagrams, and require complex processing at the receiver
before text can be recovered. The "text/t140" format is arguably
justified since packets contain plain text in UTF-8 format, and can be
directly displayed once they have been received.
The discussion of our use of the "text" top level type led to a review
of our other uses of media types with RTP. It was noted that the rules
for media type registrations don't currently allow for domain specific
types: it is not legal to register a media type saying "this type is
defined only for use over RTP". This conflicts with the rules in RFC
3555, and affects all the media types registered for use with RTP.
After much discussion between the chairs, area directors, and MIME
experts, it was concluded that is it appropriate to relax the rules
for
media type registrations in two ways:
- Allow domain specific media type registrations
- Allow complex text formats, provided they have restricted domain
of applicability and do not affect backwards compatibility for
email clients
This change will be discussed on the <ietf-types at iana.org> mailing
list.
These updates will allow us to continue basically unchanged with our
use of
media types in AVT. However, they will take time to complete, since we
must update the media type registration rules for both MIME and RTP.
The immediate consequence for the AVT working group is that the
publication of draft-ietf-avt-text-red-05.txt may be slightly delayed
(we do not expect any change to this draft, but it cannot be published
until the MIME type registration rules have changed). In addition, the
media type registration guidelines in RFC 3555 will need to be
updated.
The chairs will co-ordinate this - please contact us if you have any
questions on the change.
In future, as new RTP payload formats are developed, we will require
expert
review of the media type registration as part of the working group
last
call process. Please contact the chairs for guidance on the procedure
for this review, when you believe your draft is ready for working
group
last call. We will not forward drafts to the IESG for publication
unless they have received such review.
--
Colin Perkins
http://csperkins.org/
_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt