Re: [aqm] ping loss "considered harmful"

Mikael Abrahamsson <swmike@swm.pp.se> Wed, 04 March 2015 08:12 UTC

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Date: Wed, 4 Mar 2015 09:12:02 +0100 (CET)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Dave Taht <dave.taht@gmail.com>
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Cc: Wes Felter <wmf@felter.org>, "aqm@ietf.org" <aqm@ietf.org>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, bloat <bloat@lists.bufferbloat.net>
Subject: Re: [aqm] ping loss "considered harmful"
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On Mon, 2 Mar 2015, Dave Taht wrote:

> I note that there are conflicting definitions of CS1 (background). 
> Comcast, re-marks about 90% I see to CS1 from whatever it was 
> originally, in the hope that it is treated as background. The ancient 
> firmware in commercial home routers *prioritizes* CS1 on etheret and 
> *deprioritizes it* on wifi, into the 802.11e background queue, when 
> enabled. CeroWrt tries to cons

This is the default I have seen in quite a few 4 queue L2 devices, I 
believe it comes from IEEE recommendations:

https://community.extremenetworks.com/extreme/topics/default_802_1p_priority_to_transmit_queue_mapping

     Product           802.1p Priority/CoS    Transmit Queue

Matrix N; non-Policy Priority, 'show port priority-queue'
  -4 or 8 queues-              0      4&8 Qs-> 1
     Fast Ethernet ports       1               0
                               2               0
                               3               1
                               4               2
                               5               2
                               6               3
                               7               3

Since a lot of products will mark IP PREC part of TOS directly into .1p 
bits, this means CS0 and CS3 goes into higher priority queues compared to 
CS1 and CS2.

http://www.hp.com/rnd/device_help/help/hpwnd/webhelp/HPJ4121A/qos_priority_map.html 
seems to indicate HP does the same.

http://alliedtelesis.com/manuals/GS900M_Series_Web_Browser_User_Guide_revA/aw1001299.html 
says the same.

However, I find devices that do differently by default as you have already 
discovered.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se