[Codel] why RED is not considered as a solution to bufferbloat.

sahil grover sahilgrover013 at gmail.com
Tue Feb 24 12:29:41 EST 2015

Thanks a lot Jonathan,Eddy and Richard.
With the help of you people i have cleared many concepts.
But still one point is not clear.
Richard Sir you said that Codel is better in notifying congestion to TCP
But Sir how,i know codel does it at dequeue stage while RED does at enqueue
The thing is  congestion signal has to traverse the buffer.
Then how does it make difference that whether it is at enqueue or dequeue.i
mean how it is quicker with codel?

On Tue, Feb 24, 2015 at 8:33 AM, Richard Scheffenegger <rscheff at gmx.at>

>  Sahil.,
> Codel tries to address the problems that RED couldn't; First, the input
> signal into the algorithm (sojourn time vs. average queue depth) is of a
> different quality; Second, Codel (in it's plain form) does drop/mark on
> dequeue, while RED drops/marks on enqueue. This means, that [TCP]
> congestion control loop is much quicker with Codel over RED; thus the
> reaction by the sender will probably be timely and relevant for that
> congestion epoch.  With RED; the congestion signal (that lost packet) has
> to traverse the filled-up buffer first, thus the control loop time is much
> larger (includes the instantaneous queue length of the buffer) - and is
> further delayed by the averaging going on.
> Codel, by design, doesn't need to be tuned specifically for one particular
> drain rate (bandwidht) of the queue - unlike RED; So it adjusts much better
> to variable bandwidth MACs (Wifi, DOCSIS).
> I've been told, that RED is easier to implement in HW due to that action
> being all done on enqueue. With PIE, there exists another AQM that tries to
> re-use the hw engines that exist for RED, but the control algorithms try to
> use a different input signal - making the best of that.
> If you follow the AQM work in IETF, there is strong consensus steer to
> these more modern AQMs.
> Best regards,
>   Richard
> ----- Original Message -----
> *From:* sahil grover <sahilgrover013 at gmail.com>
> *To:* Jonathan Morton <chromatix99 at gmail.com>
> *Cc:* codel at lists.bufferbloat.net
> *Sent:* Tuesday, February 24, 2015 5:20 PM
> *Subject:* Re: [Codel] why RED is not considered as a solution to
> bufferbloat.
> So we can say Codel is better than other AQM???
> On Tue, Feb 24, 2015 at 9:24 PM, Jonathan Morton <chromatix99 at gmail.com>
> wrote:
>> Simply put, RED is a very old algorithm, one of the first viable AQM
>> algorithms. However, it proved to be so difficult to configure properly
>> that almost nobody uses it, even though many carrier grade routers
>> implement it.
>> Codel not only performs better than an ideally configured RED, but is far
>> easier to configure. This makes it much more deployable.
>> - Jonathan Morton
>  ------------------------------
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