Re: [aqm] ping loss "considered harmful"

David Lang <david@lang.hm> Mon, 02 March 2015 23:15 UTC

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From: David Lang <david@lang.hm>
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To: Joe Touch <touch@isi.edu>
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Cc: Brian Trammell <ietf@trammell.ch>, bloat <bloat@lists.bufferbloat.net>, Dave Taht <dave.taht@gmail.com>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] ping loss "considered harmful"
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On Mon, 2 Mar 2015, Joe Touch wrote:

> On 3/2/2015 1:40 AM, Brian Trammell wrote:
> ...
>> The real solution is to create a utility called "ping" that uses
>> traffic that gets prioritized the same way as the traffic you care
>> about instead of ICMP echo request/reply. Users don't care about
>> the packets on the wire so much as they do that you're supposed to
>> ping things.
>
> There are three separate problems:
>
> 1. a ping that doesn't use ICMP
> 	there are dozens of these
>
> 2. needing a reflector
> 	ping gets around this only because the reflector is widely
> 	deployed (and integrated into most OSes)
>
> 3. using the same port as the traffic you care about
> 	transport protocol is only one problem (ICMP being a "transport
> 	protocol" by virtue of using the IP protocol number field)
>
> 	the other is differential prioritization based on port number
>
> 	there's no easy solution to that;
> 	every service would need an integrated
> 	ping reflector
>
> I suspect #3 is the ultimate killer of this idea.

The service you are trying to contact acts as a reflector for TCP traffic. If 
you send a syn you will get back a syn-ack from the TCP stack of the receiving 
system.

For UDP systems, it gets more interesting and service specific. But for TCP 
systems it works today.

David Lang