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From: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To: Forums1000 <forums1000@gmail.com>
References: <CANfPCkU91zn-_oVSJyaN0_BukKY4YSCzagB=V5GwuocQYuowdw@mail.gmail.com>
Date: Mon, 12 May 2014 22:21:37 +0200
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	(Forums's message of "Mon, 12 May 2014 09:11:10 +0200")
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Cc: bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] How is bufferbloat prevented/fixed for UDP?
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Forums1000 <forums1000@gmail.com> writes:

> 1) With UDP, you cannot uniquely identify a flow? This prevents an
> AQM-algorithm to drop packets for an (several) offending UDP flow(s).

For most cases UDP flows are determined by port number pairs, same as
TCP. Multiple flows can be multiplexed over one "connection", but this
is no different from TCP.

> 2) Unlike TCP, UDP does not back down when encountering packet loss

This is true; i.e. not back-off mechanism is built into the protocol.
However, it is quite possible to build in such a mechanism in whatever
protocol is running *on top of* UDP. Indeed this is done for things like
real-time media protocol, and also bittorrents uTP protocol runs on top
of UDP.

So I guess the answer is "it all depends".

As an aside, if you *do* have an unresponsive UDP flow (whether
misconfigured or malignant), having a flow queueing mechanism like that
of fq_codel helps a lot; the bad UDP flow is then isolated and only
hurts itself, so to speak. :)

-Toke

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