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Re: [Hls-interest] FYI: new LL-HLS over HTTP/3 prioritization proposal

Lucas Pardue <lucaspardue.24.7@gmail.com> Mon, 12 October 2020 19:54 UTC

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From: Lucas Pardue <lucaspardue.24.7@gmail.com>
Date: Mon, 12 Oct 2020 20:54:20 +0100
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To: Roger Pantos <rpantos=40apple.com@dmarc.ietf.org>
Cc: hls-interest@ietf.org
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Subject: Re: [Hls-interest] FYI: new LL-HLS over HTTP/3 prioritization proposal
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Hi Roger and LL-HLS folks,

I'm one of the editors of the Extensible Priorities document. Roger's given
a salient and accurate description but I thought I might provide a little
bit more color.

HTTP/2 provided a very expressive scheme to communicate priorities:
dependencies and weights. A server can use this to schedule resources,
typically bandwidth allocation of concurrent responses. But they also have
to trade off what a client wants against local operator concerns like
preventing DoS.

Getting prioirites right is hard and some implementations never really got
it right with HTTP/2. HTTP/3 made things harder because QUIC provides no
ordering across streams; that breaks dependencies in fun ways.

This lead the QUIC and HTTP WGs to Extensible priorities, a simplified
scheme that can be applied to both HTTP/2 and HTTP/3.

Both tree priorities and extensible priorities focus on signalling, and
leave a lot of details about scheduling to the server. I think Roger's
proposal is equally applicable to either priority scheme. Detailing
effective, application-specific ordering and bandwidth allocation
recommendations for servers irrespective of client signals.

I do encourage comments here or on the issue.

Cheers
Lucas


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