Re: [rtcweb] Prioritization

Dave Taht <dave.taht@gmail.com> Wed, 30 April 2014 21:46 UTC

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Date: Wed, 30 Apr 2014 14:46:01 -0700
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From: Dave Taht <dave.taht@gmail.com>
To: "Matthew Kaufman (SKYPE)" <matthew.kaufman@skype.net>
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Cc: "Cullen Jennings \(fluffy\)" <fluffy@cisco.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Prioritization
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On Wed, Apr 30, 2014 at 2:36 PM, Matthew Kaufman (SKYPE)
<matthew.kaufman@skype.net> wrote:
>
>> -----Original Message-----
>> From: Martin Thomson [mailto:martin.thomson@gmail.com]
>> Sent: Wednesday, April 30, 2014 2:23 PM
>> To: Cullen Jennings (fluffy)
>> Cc: Matthew Kaufman (SKYPE); Simon Perreault; rtcweb@ietf.org
>> Subject: Re: [rtcweb] Prioritization
>>
>> On 30 April 2014 14:09, Cullen Jennings (fluffy) <fluffy@cisco.com> wrote:
>> > On Apr 25, 2014, at 11:03 AM, Matthew Kaufman (SKYPE)
>> <matthew.kaufman@skype.net> wrote:
>> >
>> >> If a "lower priority" packet is dispatched before a "higher priority" packet
>> in order to "prevent starvation", then what does "higher priority" mean?
>> >
>> > I think the labels reflect what "might" happen on average and not for any
>> particular packet.
>>
>> I think that Matthew was referring to the part where the browser is involved.
>> That is, the bit where, when presented with the option to send just one
>> packet from buckets A through D, how does it choose from those buckets.
>>
>> The implication was that if A is more important than B, then if A wants to
>> send, it gets to send.  Period.  The "prevents starvation"
>> view of the world says that work is shared between A-D, with increasingly
>> large proportions of the available capacity given to higher priority streams.
>> The problem with both these models is that they are crap in various ways.  In
>> one, you get cases where lower priority stuff never happens, even if that
>> isn't what you wanted; in another, lower priority stuff can get resources, and
>> that wasn't what you wanted.

It is extremely rare that you want a starvation queue. Two examples are
holding a port open through a natted device, and your typical keepalives.

If you want to support near-starvation queues, you could specify an outer
bound for the maximum time a lower priority queue can be starved.

otherwise a system of weights seems more appropo.

>> The DSCP markings and how they might interact with this are just an
>> additional layer of uncertainty, primarily.
>
> Accurate summary of my position.
>
> Matthew Kaufman
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb



-- 
Dave Täht

NSFW: https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_indecent.article