[R-C] Modular Congestion Control in rtcweb

[Michael Welzl]

On Mar 28, 2012, at 11:33 AM, Piers O'Hanlon wrote:

>
> On 28 Mar 2012, at 10:33, Eggert, Lars wrote:
>
>> On Mar 28, 2012, at 9:56, Piers O'Hanlon wrote:
>>> It may well have been covered already but since SCTP is already  
>>> proposed for data transport and it supports unreliable transport  
>>> and has some support for pluggable congestion control then if one  
>>> could specify RTP over SCTP which could provide another possible  
>>> approach? It could also potentially simplify some aspects of inter- 
>>> stream congestion control.
>>
>> I think that the SCTP BSD *implementation* has pluggable congestion  
>> control (because Lawrence Stewart added that for TCP and SCTP  
>> benefits as a side effect.) I don't think the SCTP *spec* has  
>> support for pluggable congestion control. AFAIK only the DCCP spec  
>> has pluggable congestion control.
>>
>> (And note that I personally have no strong feelings about SCTP vs.  
>> DCCP for rtcweb. I just want to make sure that we have all the  
>> facts when we decide.)
>>
> Ok - I wasn't quite clear on SCTP's support for pluggable CC -  but  
> having looked at the SCTP RFC I can see it is not part of the spec.  
> I had wondered about the multipath-SCTP providing support but that  
> doesn't either. Having seen pluggable CC for SCTP implementations  
> for BSD, LInux, and Solaris, it seemed it wasn't too hard - and may  
> have some of the benefits I mentioned, but since it would need  
> additional specification then one could use something else...

Just as a datapoint, working pluggable CC for Linux SCTP (in the  
kernel) doesn't seem to exist, I think, or at least it didn't one year  
ago when we made it but never really finished... see my related  
message to TSVWG yesterday:
http://www.ietf.org/mail-archive/web/tsvwg/current/msg11212.html

I also have no strong personal feelings on DCCP vs. SCTP and see your  
point about the benefits. Then again, DCCP was brought up in this  
discussion because it can negotiate congestion controls, and that  
functionality isn't there in SCTP, because pluggable CC. in SCTP isn't  
a part of the standard, as Lars said.

Cheers,
Michael