[R-C] Modular Congestion Control in rtcweb

[Luca De Cicco]

It's not clear to me how this discussion is developing: is there any
consensus about making congestion control modular in webRTC (which was
the original discussion here)?

I'm asking this because the discussion rapidly changed topic from
"should we make congestion control pluggable?" to "is DCCP a good
candidate?" to "what congestion control should we use?" and I just
feel kinda lost in these parallel discussions.

Thanks,
Luca

On Wed, Mar 28, 2012 at 2:13 PM, Piers O'Hanlon <p.ohanlon at gmail.com> wrote:
>
> On 28 Mar 2012, at 11:42, Michael Welzl wrote:
>
>>
>> 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
>>
> Yes I'd seen your one -  It was interesting - I wasn't implying that they were 'finished' and had made it into the main kernel.
>
> Though the userland SCTP stack from sctp.fh-muenster.de runs on Linux, BSD. OSX and Windows and it seems to have APIs in place for pluggable congestion control (though it seems to be limited in alternative algorithms for now). Since the RTCWeb folks are keen on userland approaches then this is more promising.
>
> Piers
>
>> 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
>>
>