[Codel] FQ_Codel v. FQ_LQD

James Roberts James.Roberts at inria.fr
Tue Feb 12 04:29:45 EST 2013

I have not been following Bufferbloat but a colleague forwarded to me the latest post from Dave Täht about FQ_Codel. It is good to see the virtues of fair queuing are being rediscovered. 

I think the work by Suter and co-authors on FQ in high capacity routers is particularly relevant:

B. Suter, T. Lakshman, D. Stiliadis, A. Choudhury, Buffer Management Schemes
for Supporting TCP in Gigabit Routers with Per-Flow Queuing, IEEE Journal in
Selected Areas un Communications, August 1999. (http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=772451)

They may have been the first to introduce "head drop". Actually they advocated dropping from the front of the flow queue with longest backlog (FQ_LQD). I am not sure why a more sophisticated AQM, like RED, ARED or Codel, is better than longest queue drop.

Another advantage of FQ_Codel highlighted in the report by Toke Høiland-Jørgensen (notified on the list) is to give priority to packets of newly active flows. This idea was already proposed in our papers:

A. Kortebi, S. Oueslati and J. Roberts. Cross-protect: implicit service differentiation and admission control,  IEEE HPSR 2004, Phoenix, USA, April 2004. 
A. Kortebi, S. Oueslati, J. Roberts. Implicit service differentiation using Deficit Round Robin,  Proceedings of ITC 19, Beijing, August 2005. 

I have long been advocating per flow fairness as the basis of effective traffic control so I hope you won't mind me recalling this prior work.

Jim Roberts

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