Re: [aqm] [tcpm] TCP ACK Suppression

Dave Taht <dave.taht@gmail.com> Sat, 10 October 2015 23:06 UTC

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Date: Sat, 10 Oct 2015 16:06:33 -0700
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From: Dave Taht <dave.taht@gmail.com>
To: David Lang <david@lang.hm>
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Cc: "tcpm@ietf.org" <tcpm@ietf.org>, Joe Touch <touch@isi.edu>, "mallman@icir.org" <mallman@icir.org>, "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <wolfram.lautenschlaeger@alcatel-lucent.com>, Greg White <g.white@cablelabs.com>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] [tcpm] TCP ACK Suppression
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I have been busy with other matters and unable to keep up on this thread.

I just wanted to say that I'm with dlang here... aggregated and
asymmetric transmits in wifi, cell, and cable, are here to stay. Deal
with it.

I would certainly have preferred a wifi world that instead of all
stations and APs highly contending for bursty access to a single
320mhz channel, we had 160 dedicated, low latency, 5mhz channels, but
that is not what the IEEE has handed us.


On Fri, Oct 9, 2015 at 10:58 PM, David Lang <david@lang.hm>; wrote:
> On Fri, 9 Oct 2015, Joe Touch wrote:
>
>> On 10/9/2015 7:14 PM, David Lang wrote:
>>>
>>> The problem with proposals like that is just like RFC3449 says, the
>>> source can't know what the network looks like to decide if there is a
>>> benefit to reducing ACKs.
>>
>>
>> To understand your position, is your conclusion that if it benefits a
>> single place in the network, then that's enough of a view to know that
>> it's safe and beneficial throughout the network?
>
>
> No.
>
> But when something shows clear beneifts when deployed, clear problems need
> to be identified to counter those benefits, or alturnative methods of
> solveing the problem need to be shown.
>
> I didn't know about it initially (I was working from experience and logic),
> RFC3449 has explored many of the problems that cause and result from fewer
> than 1 ACK per 2 data packets, including worrying about the timing of the
> ACK packets.
>
> As much as you seem to want to make this discussion about cable modems and
> highly assymetric links, this discussiona ctually started  from the position
> of packets in a particular flow being sent in bursts due to non-endpoint
> related reasons. It started with AQM queues, but radio networks (Wifi and
> Cell) have similar behavior (packets queue until a transmit window is
> available, tehn a bunch are sent at once)
>
> Cable modems were introduced to the discussion to counter the thought that
> sending fewer ACKs would destroy the Intenet.
>
> RFC3449 doesn't completely address the current situation, but it provides a
> very good place to start, and it seems to me that the solitions it explores
> to address the conerns that it (and you) raise are actually being addressed
> pretty completely. There are still some areas to talk about (ECN interaction
> for example) and we wshould be talking about those issues rather than
> arguing that the proposal violates holy writ.
>
> you want a network where packets are just forwarded with no modification and
> no delays. Unfortunantly such a network does not match the real world any
> longer (and it only approximated the real world in the first place) Shared
> media networks have existed since the earliest networking days. What is
> changing is theratio between the data speed when transmittingand the time
> available to transmit. Given the same number of stations in an area, I'll
> bet that old thinnet ethernet at 10Mb/s spent a significantly higher
> percentage of the time transmitting data than current Gb/s and immediate
> future 10Gb/s wireless networks. Just like wired network speeds are climbing
> with the MTU staying the ame, wireless network data rates are climbing but
> the time available for a given station is remaining the same (or shrinking),
> so the number of packets that get delayed until the next transmit slot are
> only going to keep climbing, no matter what anyone wants.
>
> The asymmetrical nature of the networks is just addng insult to injury, not
> the cause of the issues.
>
> Wireless networks are gaining the ability to transmit to multiple stations
> at once. But the nature of usage patterns and the physical geometry of the
> wired vs mobile ends of the link make the reality that only the wired end
> can effectively make use of this capability. this makes the availble
> downstream bandwidth on a network fabric grow much faster than the available
> upstream bandwidth. To some extent this will put less stress on the upstream
> side of the wired network it's attached to, but it will mean that the demand
> for mobile station transmit slots is only going to multiply. Just reducing
> the number of timeslots the base station uses isn't the answer because that
> will add latency to all the data downloads.
>
> IIRC, I saw a story today where one of the contenders for 5G cell networks
> is already at a ratio of 24:1 or worse.
>
> David Lang
>
>
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