Re: [Dart] ICE might send your traffic over TCP

Jonathan Lennox <> Thu, 24 July 2014 13:00 UTC

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From: Jonathan Lennox <>
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Thread-Topic: ICE might send your traffic over TCP
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Date: Thu, 24 Jul 2014 13:00:49 +0000
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Subject: Re: [Dart] ICE might send your traffic over TCP
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I don’t think different drop precedences would be useful in respect to TCP.

The problem is that the way the WebRTC APIs are structured, it’s not necessarily clear to an application that its media traffic is indeed going over TCP, so it might make precedence requests that the browser implementing the APIs can’t (and shouldn’t try to) satisfy.

The question is how the browser should behave when that happens.  I spoke to Cullen about this, offline, after the DART session, and I believe he had a simple proposal.

On Jul 24, 2014, at 3:54 AM, wrote:

> Jonathan,
> Let's briefly discuss your point below: Different drop precedences are required if congestion within a PHB group may occur. TCP is designed for reliable transport. In case of a loss, TCP will reduce bandwidth and retransmit the dropped information. I'm not an RTP expert. The few applications known to me don't seem to benefit from such a behavior, if a single application flow uses different drop precedence levels in combination with TCP.
> It may make sense to have different TCP flows marked by different drop precedences. The less important TCP flows get throttled in the case of congestion. But is there a need to avoid re-ordering across different drop precedences, which is an AF PHB group feature? Again, I'm not an RTP expert - but that doesn't sound like making a lot of sense too. 
> In general, I'd be interested to learn, if some applications were benefitting from ECN (or a congestion indication by marking rather than by dropping). Independent from the question whether they use TCP or RTP transport. 
> Regards,
> Ruediger
> -----Message-----
> From: Dart [] On behalf of Jonathan Lennox
> Subject: [Dart] ICE might send your traffic over TCP
> [snip]
> How (say) a WebRTC implementation should handle API requests for multiple drop precedences when the underlying ICE channel is TCP is unclear to me.
> Jonathan Lennox