Registration review for vnd.americandynamics.acc
gsands at tycoint.com
Fri Dec 14 12:15:12 CET 2007
Thanks for your advice. I'll submit the registration request with your
suggestions for RTP only as follows.
Type name: video
Subtype name: vnd.americandynamics.acc
Required parameters: rate (RTP only)
Optional parameters: none
Encoding considerations: This media type is framed binary data (see
RFC 4288, Section 4.8)
Security considerations: ACC is a binary file format that contains no
active content and no textual information.
Interoperability considerations: none
Published specification: none
Applications that use this media type: Intellex DVMS, Intellex
File extension(s): acc
Macintosh file type code(s):
Person & email address to contact for further information: gsands AT
Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP (RFC 3550). Transfer within
other framing protocols is not defined at this time.
Author: gsands AT tycoint.com
Change controller: gsands AT tycoint.com
Tyco Safety Products/CEM Systems Ltd.
Registered in Northern Ireland: NI 25728. Registered Office: Unit 4 Ravenhill Business Park, Ravenhill Road, Belfast, BT6 8AW..
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From: Colin Perkins [mailto:csp at csperkins.org]
Sent: 12 December 2007 18:38
To: Sands, Gary
Cc: ietf-types at iana.org
Subject: Re: Registration review for vnd.americandynamics.acc
On 10 Dec 2007, at 14:23, Sands, Gary wrote:
> My intention was to register this type for RTP use only - hence my
> statement for "Restrictions on usage" that the type could be
> transmitted over RTP. I was following RFC 4855 Section 2 part (a)
> "Not yet registered as a media type" (or so I thought) by stating
> it defined for RTP transfer and saying nothing else.
> It probably would be better phrased as "This type may *only* be
> transmitted over RTP". Admittedly the original statement is rather
> terse and the comment for "Encoding considerations" about non-
> binary transports may have implied the possibility of other
> transport methods.
Right - I read the registration as allowing transfer over RTP, but
not being restricted to that environment.
> If someone wanted to use a media sub-type over other transports
> would a statement for "Restriction on usage" such as the following
> "Restrictions on usage - This type may be transmitted over RTP.
> However the file format is equivalent to the concatenated sequence
> of payloads from RTP packets not including the RTP headers or any
> RTP payload-format headers. Therefore the type may be shared for
> non-RTP file-based transmission. The file format may/shall include
> a magic number/header at the start of the file that is not included
> when the data is transferred via RTP."
If the intent is to register a type for use with RTP only, then the
usual approach is to state "This media type is framed binary data
(see RFC 4288, Section 4.8)" under Encoding Considerations (this is
different to binary data, since it requires knowledge of the framing
protocol to make sense of the data), and in Restrictions on usage,
state "This media type depends on RTP framing, and hence is only
defined for transfer via RTP (RFC 3550). Transfer within other
framing protocols is not defined at this time".
If you want to define framing for other environments, that's
appropriate given the constraints from RFC 4855 section 2.2 (that the
media data is the same in all cases, and only the framing protocol
differs), but you need to change the wording to indicate what types
of framing are acceptable, and specify how the framing protocols
encapsulate the media type. This can be done in the Restrictions on
Use section, stating something similar to "This media type requires
knowledge of the framing mechanism to interpret the data. RTP [RFC
3550] provides one appropriate framing protocol. Alternatively, a
sequence of complete frames may be concatenated preceded by the magic
number [whatever] for file storage, or for transport over reliable
byte stream protocols".
It would be helpful if the RTP payload format or details of the media
format were publicly documented. The IETF AVT working group can give
advice on the development and publication an RTP payload format, if
desired. Note: this doesn't require publishing the codec specification.
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