8/8/2019 Paper5 Review CS536

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Paper review

Floyd, Sally; Jacobson, Van (August 1993). "Random Early Detection (RED) gateways for CongestionAvoidance". IEEE/ACM Transactions on Networking 1 (4): 397-413. doi:10.1109/90.251892

The paper presents Random Early Detection(RED) gateways for congestion avoidance in packetswitched network. The main goal of RED is to provide congestion avoidance by controlling the averagequeue size. Additional goal includes the avoidance of global synchronization and of a bias againstbursty traffic and the ability to maintain average queue size even in the absence of co-operation fromtransport layer. The key argument put forward by the authors is that the most effective detection ofcongestion can occur in the gateway itself as only the gateway has the unified view of the queuingbehavior over time.

The authors have briefly discussed the previous work on the congestion avoidance gateways andhighlighted the anomalies with early methods like global synchronization ad bias against bursty trafficand how RED has addressed those challenges. The proposed method RED is a different approach forcongestion avoidance in a way that it has different method for detecting congestion and for choosingwhich connection to notify of this congestion. Firstly the author quoted a study be Hashen[11] to pointout the short comings of Random drop and Drop tail gateways , that they drop each packet arriving atthe gateway with a fixed drop probability. This approach results into issue of global synchronization inthe network. Then the paper highlighted an improvised method called Early Random Drop Gatewayswhich drops each arriving packet with probability of 0.02 , however the study by Zhang[36] shows thatthis version was not successful in controlling the Mis-behaving users. Finally the paper compare indetail the difference between DECbit congestion avoidance scheme and RED.

The paper has provided the mathematical formulation and design details of RED algorithm andcalculated the parameters like average queue length and the packet marking probability. The proposedconcept of RED has been verified and backed through a simple simulation of multiple FTPconnections comparing drop tail and RED algorithm. Finally authors analyzed and verified theeffectiveness of RED algorithm in providing fairness to bursty traffic and handling of Mis-behavingusers.

The most important point highlighted in this paper was the method of notifying congestion to aconnection. The probability that a connection is notified of the congestion is proportional to that ofconnection's share of throughput through the gateway. This is a really effective approach to avoid a biasagainst the bursty traffic. Another important factor is deploy-ability of the RED approach as thegateway can mark packet by dropping them, rather then setting a bit in the packet header thus the REDgateway controls the average size even in the absence of a cooperating transport protocol. Thus it canbe implemented gradually in the current TCP/IP networks with no change to transport protocols.Another interesting but not so important fact that has been highlighted is RED gateways can be usefulwith a range of packet scheduling and packet dropping preference algorithms.

The paper is well presented and supported , however it left some points open ended like how theperformance will be impacted if we deploy RED in some section of networks and other section hassome other technique like Drop Tail. Also what should be the average queue size and alsoimplementation details are not discussed in concrete manner.

http://www.icir.org/floyd/papers/early.twocolumn.pdfhttp://www.icir.org/floyd/papers/early.twocolumn.pdfhttp://www.icir.org/floyd/papers/early.twocolumn.pdfhttp://www.icir.org/floyd/papers/early.twocolumn.pdf