[Codel] About Packet Drop in Codel

[divya singla]

But Sir i heard that UDP does not respond to congestion.Even though its
packets are lost, it keeps sending packets at the same rate(unlike tcp)

-- please answer this too:
 Does codel implement concept of marking(ECN)  in ns2?


On Tue, Mar 3, 2015 at 12:37 AM, Jonathan Morton <chromatix99 at gmail.com>
wrote:

> With UDP, you're at the mercy of the application using it. With TCP,
> you're merely at the mercy of the operating system.
>
> AQM acts on UDP packets in the same way as TCP packets - in fact it can't
> tell them apart. So any application which detects and responds to UDP
> packet loss in the same way as TCP does, will back off just the same.
>
> In practice, UDP is used for several different types of application:
>
> - simple request response, such as DNS and NTP, where eliminating TCP's
> connection setup overhead is important. In any case, TCP's congestion
> control doesn't get a chance to do any good on such s short-lived
> connection. Packet loss in this situation is tolerated by retry, with
> exponential backoff as an alternative congestion control measure.
>
> - latency sensitive and often isochronous (inelastic) flows like VoIP.
> Packet loss may lead to a loss of quality, but there is little the
> application can do to reduce its loss except dropping the call completely.
>
> - as a way to implement delay sensitive and pacific congestion control
> algorithms, as in uTP.
>
> A flow isolation system, such as that in fq_codel, will often leave UDP
> flows alone completely, because they tend not to be the ones using the bulk
> of the bandwidth. Conversely, if a single UDP flow was responsible for the
> congestion, it would let the other traffic bypass it. This is why fq_codel
> is better than just plain codel, if you can get it.
>
> - Jonathan Morton
>
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