Subject: Re: I-D ACTION:draft-iesg-media-type-00.txt

From: Bruce Lilly <[email-masked]>
Date: Fri, 1 Jul 2005 15:36:47 -0400

>  Date: 2005-07-01 11:38
>  From: Magnus Westerlund <[email-masked]>

Magnus,

you wrote:
> I think there are good reasons for keeping the registry as one.

Let's look at your reasons:
> Both in  
> RTP and MIME usage the types are after all media formats with specified 
> represenations.

That's a good reason to have registries which share certain
characteristics, but it does not require sharing the same
registry and namespace.

> Having one registry with all representation instead of  
> separating does not simplify the process of maintaining good usage of 
> that registry and avoid duplicating entires when there actually are two 
> different representations.

I'm not sure that I completely understand what you mean.  Anyway:

If there is a single registry:
o each MIME and each RTP implementer will have to examine each entry
  and determine:
  * is this media type applicable to my work?
    - yes
    - no
    - unclear
  This is clearly more work for implementers if there is a combined
  registry.  To the extent that implementers ask questions ("what's
  this 'framed' stuff?"), it may be more work for registered contacts
  also.
o the registration procedures, forms, review forum, etc. will have
  to accommodate items which are the union of items which are
  individually applicable to different uses
  * MIME registrants will continually ask "what is this 'framed'
    encoding stuff?"
  * RTP registrants will continually be told "your 'text' type
    is incompatible with the requirements for 'no software required',
    'fallback to text/plain', etc."
  These have been observed issues with use of the MIME registry for RTP
o if there is some media type that is usable by MIME and by RTP, it
  need only be registered once (unless of course there are differences
  in parameters, security issues, etc, in the registration form that
  would indicate separate registration)
  * the key question is, are there any such types?
    - clearly you have said that, unlike MIME media types, the RTP
      types cannot be stored in a file, etc.  So it's clear that
      the RTP types cannot be used by MIME
    - can the MIME types be used by RTP?  For example, can RTP make
      use of the MIME media type application/vnd.ms-excel?
  This would be a point in favor of a combined registry -- if and only
  if there is a reasonable number of media types usable by both MIME
  and RTP.
o if there are two types with incompatible definitions which wish
  to use the same name, there will be a clash
  * the namespace is big enough so that names aren't scarce
  * however, there may be some user-land confusion, as sometimes
    users infer more from a name that just it being a tag for something
  This is a relatively minor point in favor of separate registries.

If there are separate registries:
o RTP implementers can look through an RTP registry, without having to
  wade through MIME types and vice versa.  Likewise for any other
  registries that might be desirable
  * MIME implementers can safely ignore the RTP registry and vice versa
    - any implementer who needs to be concerned with both can of course
      look at both
  Point in favor of separate registries.
o registration procedures, forms, review forums, etc. can be customized
  for the particular needs, simplifying matters for registrants, reviewers
  (including the IESG), and IANA (e.g. if one registry needs a way to
  an "obsolete" status and others do not, there is no conflict in
  information presentation)
  * reduces the number of questions/potential for confusion among
    - registrants
    - reviewers (including IETF Last Calls if issued, IESG)
    - implementers
  Point in favor of separate registries
o if there is some media type which is usable by both MIME and RTP,
  registration would have to be duplicated (modulo differences in forms
  and so on)
  * as above, are there any?
  * copy and paste...
  * maybe some incremental work for IESG and IANA -- *IF* there are any
    such types
  Point in favor of a combined registry, if and only if there is a
  reasonable number of such combined-use media types
o no clashes in the case of incompatible definitions, even if similar or
  the same name is used, provided that MIME and RTP do not interact in
  such a way as might cause confusion about whether media is a MIME
  type or an RTP type
  * as I understand it, there is no opportunity for confusion; any
    relationship would require some sort of conversion, and a software
    or protocol entity accepts/generates either one type or the other
  * names in each realm can be convenient for users, though there may
    be some potential for user confusion about whether a type is a MIME
    type or an RTP type
  Point in favor of separate registries.

Issues which might be unclear:
o Expert reviewer/review forum workload
  * clearly there is a flow of MIME registrations; it also appears that
    there is a flow of RTP registrations
    - Is the combined total too much for one reviewer/one review forum?
    - Is there enough flow of both types to support two reviewers (reviews
      happen frequently enough that the reviewer hasn't retired or moved
      on between reviews)?
    - if the answers are:
      yes/no -- inconsistent
      yes/yes -- indicates in favor of separate registries
      no/no -- use one reviewer (doesn't matter if registries are combined
               or separate)
      no/yes -- indicates in favor of separate registries
  Either inconclusive or favors separate review forums (and registries, to
  avoid clashes).
o Expert reviewer/review forum expertise:
  * I believe that past discussion on the media types review list and here
    indicates that while reviewers are familiar with MIME issues, RTP
    issues have not always been well-understood.  While we can learn/adapt,
    separate review forums, possibly also separate reviewers might be
    more productive for all parties
  Seems to favor separate review forums, probably separate registries (to
  avoid clashes)

As I see it, most of the issues seem to favor separate registries, the
exception hinging on whether or not there are any media types which are
usable by both MIME and RTP.  If I understand the bulk of your message
correctly (which is similar to explanations made on the media types
review list some weeks ago), there aren't any.

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---

From: Magnus Westerlund <[email-masked]>
Date: Tue, 05 Jul 2005 17:18:46 +0200

Hi Bruce,

I will comment some of the arguments that you list. And if we where 
having this discussion before any RTP payload name registry existed at 
all I would definitely be tempted by separated registries. However the 
fact that we have used an IETF established policy for more than 5 years 
and registered a large amount of names (>70) makes it very hard to see 
that moving into separated registries will resolve any confusion. In 
addition it will require a huge work effort to move to the new registry.

I can also contest that AVT doesn't have a hoard of people interested in 
updating media types registrations. We can barely manage to perform 
updates of our own major RTP payload formats. When it comes to RTP 
payload formats there are always demand for new ones as new media codecs 
are defined, but the ones are already out-dated and sees less and less 
use there is little interest for. Especially to perform an exercise that 
provides no improvement.

To me the best way forward is that we clean up the registration 
procedures of the current media types registry. Clearly document the 
fact that there are at least two different usages for the media types 
registry. It will help reduce the confusion that exist and have minimal 
workload.

> characteristics, but it does not require sharing the same

The issue I see is that with two separate registries one will not 
seriously consider the names in the other registry.

> I'm not sure that I completely understand what you mean.  Anyway:

Sorry for the bad sentence structure. What I intended to stress was that 
  having cross review between registries is a hard way of avoiding 
having two different formats register the same name but in different 
registries. As the name structure looks the same, it is very hard to 
determine to which registry such a name would belong. Thus one needs to 
look up both if checking.

I think having a single registry with clearly marked usage is a 
simplification.

>   this 'framed' stuff?"), it may be more work for registered contacts

 From my perspective a implementor normally know what it needs to 
support on a fundamental level. I need to support the AMR codec. From 
that perspective looking up audio/amr in either of the registries will 
be simple. In fact this is one of the media types that are both RTP and 
file format. This would need to be doubly registered and thus needs 
links to the other registry to have people avoid taking the wrong 
version if they are lacking the necessary knowledge.

If the registry page would include columns that indicated usage of the 
media type this can easily be resolved.

>     'fallback to text/plain', etc."

These reasons you list are due to the unclarity regarding the procedure. 
If one clears this up and makes it clear what is applicable and provide 
more concrete example then I don't think it will be a big problem.

 > These have been observed issues with use of the MIME registry for RTP

What are you referring to. I don't think there has been any serious 
issues other than the ones that occur at registration time due to 
unclear process. That I think can be understood also by those 
registering for MIME usage only.

>   if there is a reasonable number of media types usable by both MIME

I think this is one of the points of contentions in the earlier 
discussions we have had regarding this topic. This in the light of 
registrations like audio/amr (RFC 3267) that are for both file format 
and RTP.

In my view the MIME and RTP usage can share huge parts of code, but they 
both needs some special adaptation. Me and Colin are not agreeing with 
Ned on what is considered required overlap between the RTP domain and MIME.

>   This is a relatively minor point in favor of separate registries.

I agree that it is not a problem if we are capable of detecting and 
keeping the review to actually look in both registries and ensure that 
the other work is not trying to use the same name.

>   Point in favor of separate registries.

I can agree with that if one comes looking at names from that direction. 
However I think the most common is that one either comes from the 
defining RFC or have the type name and want to look it up. In these 
cases separate registries do not provide any benefit. This only exist if 
you have the task of implementing all relevant audio/ types.

>   Point in favor of separate registries

However the will actually be an increase in questions as you will also 
need to ask: Are this name registered in the other registry?
If yes, is this a type that are the same or should it use another name?

>   reasonable number of such combined-use media types

There are 5 or so that are combined registered.

>   Point in favor of separate registries.

The confusion on this level do exist more in the head of implementors 
and users. Looking at the name audio/amr can you determine what registry 
it belongs in? And the answer is no, you need to have the application 
context to determine that. I think the work of educating these people is 
the same independent of one or several registries.

>   Either inconclusive or favors separate review forums (and registries, to

I agree with the concern these question raises. However from my 
perspective there will be need to have cross review between the 
different domains. Thus having two review forums will only result in 
need for coordination.

>   Seems to favor separate review forums, probably separate registries (to

I think that we need reviewers that learn to understand both issues. 
Also that appointed reviewers belong to both sides to ensure correct 
review.

> review list some weeks ago), there aren't any.

There are at least 5 types that are both RTP payload formats and file 
formats. They are all having the same smallest unit that the codec 
handles. The difference between RTP and files are that RTP uses explicit 
timing while the files are using implicit by the order the data is 
stored. Small variations in packetization do also occur and in most 
cases there are also an magic word starting the file.

There are a lot of pro and con and I don't see a lot of decisive 
arguments. Therefore I would like to point out the issue of workload. I 
think we should select the way forward that results in least work why 
still improves the situation. To me that is to keep a single registry 
and improve the registration process and information.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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