Subject: [rmcat] Review of draft-ietf-rmcat-cc-requirements-02

From: Mirja Kühlewind <[email-masked]>
Date: Wed, 12 Mar 2014 15:39:53 +0100

Hi (as individual contributor),

find below some comments. I might repeat some of the comment that have already 
be made, but I also think those points are important. 

A few general comments:
1) Would be helpful to spell out most of the acronyms and give the respective 
references as Magnus already mentioned.
2) I know you told me that the order does not have a specific meaning, but it 
might still be useful the rethink the order to e.g. group more related points 
together. Some more concrete remarks below.

More detailed comments:

Abstract:
I think the scope of the document is just right but the abstract does not 
really reflect the content very well. Let me just try to propose a different 
abstract:

"Due to an increasing amount of (RTP-based) the real-time media traffic in 
today's Internet (e.g. with the introduction of RTCweb [ref]), it is 
especially important to ensure that this kind of traffic is congestion 
controlled to provide a proper capacity sharing between different flows and 
avoid a congestion collapse. As the requirements for interactive, 
point-to-point real time multimedia are quite different from the requirements 
for traditional congestion control as developed for bulk transfers like FTP 
or bursty transfers like web, this document describes a set of requirements 
that can be used to design and evaluate such new RTP Media Congestion 
Avoidance Techniques (rmcat)."

1. Intro
s/The traditional TCP congestion control requirements were developed in
   order to promote efficient use of the Internet for reliable bulk
   transfer of non-time-critical data/
   Most of today's TCP congestion control schemes were developed with a focus 		 
   on an use of the Internet for reliable bulk transfer of non-time-critical 
   data/

100s -> ITU-T names 150ms in G.114

As already said by a couple of reviewers, please don't only point to 
rtcweb-overview but also list the relevant terminology (because this is rmcat 
and not rtcweb wg).

2. Requirements

Req 1) 
- This seems to be two requirements in one: as-low-as-possible delay and 
useful amount of bandwidth. While the useful amount of bandwidth req seems 
also be part of Req 2 and 8... maybe split up or have separate subbullets on 
these two things
- Don't really get the different between 1C and 1D...?
- s/They are often are layered/They are often layered/

Req 2)
- I agree with other reviewers that fair is not a good word here. I would 
instead say 'must be able to get a proper share of the bandwidth'.
- Then one could merge Req 8 as one point into a new requirement 2B ( or at 
least req 2 and req 8 should be listed right next to each other).

Req 3)
s/between the same endpoints/that share a common bottleneck/

Req 4) 
please spell out ECN and give a ref

Req 5)
Not sure what is actually a requirement in 5 or what are just some explanation 
on RTP. Maybe you add the assumption that we talk about RTP traffic and stuff 
that needs to be know about RTP/RTCP in the Introduction (incl. respective 
references) and make the requirements a little more clear?

Req 6)
Do not really understand what the actually requirement is -> there should be 
a 'should' somewhere....

Req 7)
no comments :-)

Req 8)
said this already: merge with 2 or move below 2

Req 9)
could potentially be merged with 4 or moved below 4

Req 10)
This is an important point which I'm, coming from CC design, didn't think 
about at the beginning. I would list this requirement right after req 2 as 
there are also some similarities.

Req 11)
Please remove, there shouldn't be a requirement for CC design that the design 
should be evaluated based on this requirement... You could add this text in 
the intro but as we have an own doc on evaluation I don't think this point is 
needed here.

Req 12)
Isn't this maybe a subbullet of 10?

4. Security
Not sure if we actually need this text here, because there is nothing specific 
for rmcat here (that's all true for cc in general) and if we really need a 
text like this, it probably should be part of the candidate document. There 
doesn't really need to be security considerations in an requirements 
document. If you really, really want to say something, than just say, that 
requiring cc for rt media is a very important for the stability of the 
Internet.

Mirja