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Review by : Haris Volos Paper : Random Early Detection Gateways for Gongestion Avoidance

Summary: Review by : Haris Volos
Paper : Random Early Detection Gateways for Gongestion Avoidance
Authors : Sally Floyd and Van Jacobson
The paper presents an active queue management technique of preventing congestion in packet-switch net-
works called Random Early Detection (RED) gateways. RED is based on the observation that congestion
can most accurately be understood at the gateway, since it can distinguish high propagation delay from
high delay brought on by increasing queue lengths. Therefore, they suggest that congestion detection
should be done at the gateway. Congestion is detected in the gateway by measuring the average queue
length, and notification of congestion to sources is done by either dropping packets or marking them. This
mechanism has some desirable properties, including not being biased against bursty traffic, and being able
to avoid global synchronization, a problem where all hosts in a network are notified of congestion at the
same time and simultaneously reduce their window size and output to the network. The key way that
RED follows to achieve the above properties is through its randomization mechanism. When packets are
marked randomly, the probability that a particular packet is marked is proportional to the bandwidth that
the connection it is on is consuming.
Concerning some weak points of the paper, I think while the paper gives some good science on the
parameters of the RED gateways, how to select the values of the parameters is an open engineering problem.
It seems to me that the network engineer has to try a lot to tune the RED gateways under different traffic
loads. Another issue is related with fairness and misbehaviour. Although RED could identify connections
using a large share of the total bandwidth using the marking-probability method, it could realize the


Source: Akella, Aditya - Department of Computer Sciences, University of Wisconsin at Madison


Collections: Computer Technologies and Information Sciences