Dear Harald, just to be clear, I was considering DCCP (at userspace) only because it supports pluggable congestion control (which was the main point of the thread "Modular congestion control"), so that it could be used as a starting point at least for the definition of a common interface for congestion control algorithms. Cheers, Luca On Wed, Mar 28, 2012 at 11:20 PM, Harald Alvestrand <harald@alvestrand.no> wrote:
If you are thinking of DCCP as "DCCP in the kernel, using proto=33 on the network", the answer is simple: This is not deployable as a part of a browser deployment.
Browsers are deployed fairly rapidly across the Net, but have to run on a variety of platforms, and have no control over the platform they run on. Installing a new protocol is not an option; limiting deployment to the subset of the market that supports DCCP today, and is behind firewalls and NATs that do the right thing with DCCP now (or within 12 months) is also not an option.
So DCCP in the kernel is not compatible with the goals of RTCWeb.
DCCP over UDP is more realistic to deploy, given that UDP already passes firewalls. This is the major reason why, for a peer-to-peer data protocol, the SCTP/DTLS/UDP stack was felt to be a reasonable option; another major factor was the fact that we have code for an userland stack that is known to run on several OSes already available.
Given the lack of tested userland stacks for DCCP, and the wide availability of userland stacks, protocol analyzers and other tools for RTP over UDP, the RTCWEB WG chose to not investigate the use of DCCP for RTP transport any further.
Others who were part of that discussion may have more to contribute.
Harald
On 03/27/2012 03:15 PM, Luca De Cicco wrote:
Well, that's a good point, of course there are pros and cons here.
The pro is that using the socket interface is super-simple from the application point of view, the downside (and that's a though one) is that having a new protocol developed for an operating system is not a piece of cake. For what I know, DCCP is only supported by the Linux kernel as of today.
I think developing the congestion control in the userspace is still a good idea to speed up deployment.
Cheers, -- Luca De Cicco, PhD, Eng. Politecnico di Bari Dipartimento di Elettrotecnica ed Elettronica Via Re David, 200 - Bari - ITALY Office: +39 080 596 3851
On Tue, Mar 27, 2012 at 3:00 PM, Wesley Eddy<wes@mti-systems.com> wrote:
I think the first question that should be answered is why not just use DCCP where this modularity already exists.
I think the answer might be that if you buy the requirement to operate across multiple flows, and that you're doing the muxing of them via RTP, then the feedback also needs to come via RTP rather than on an aggregate below that DCCP might provide.
This should probably be discussed though.
On 3/27/2012 8:46 AM, Luca De Cicco wrote:
Well, I guess the first step is to define an interface that congestion control modules should use. We could base this effort on the requirements defined in draft-jesup-rtp-congestion-reqs.
From the implementation point of view, we should discuss how to distribute congestion control algorithms. Should we allow distribution of cc algos as browser plug-ins to extend the ones standardized by the webrtc effort?
What do you think?
Cheers, -- Luca De Cicco, PhD, Eng. Politecnico di Bari Dipartimento di Elettrotecnica ed Elettronica Via Re David, 200 - Bari - ITALY Office: +39 080 596 3851
On Tue, Mar 27, 2012 at 2:24 PM, Wesley Eddy<wes@mti-systems.com> wrote:
On 3/27/2012 7:25 AM, Luca De Cicco wrote:
Dear all,
this mail follows a thread I've recently started at rtcweb@ietf.org. and moved to this mailing list following Harald's suggestion.
Since congestion control is a fundamental building block for a multimedia communication framework such as webrtc, I think it makes sense to design the framework to allow using different congestion control algorithms such as it is done with audio/video codecs.
Are there any plans to make the congestion control algorithm modular for multimedia transmission via PeerConnections?
This would require the peers to select a particular congestion control algorithm at the establishment of the PeerConnection similarly to how the DCCP [1] protocol does at kernel level.
It seems like a good idea to me, in order to make it potentially easier to deploy upgrades to the algorithms over time (especially since it seems that the algorithms will start as question marks).
This also motivates the question of why RTP over DCCP isn't a potential solution.
-- Wes Eddy MTI Systems
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-- Wes Eddy MTI Systems
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