Buffer Management: - Random Early Detection (RED)

Posted by AJ × 07:35

*An approach to preventing unfair buffer hogging by detecting congestion when a

buffer begins to reach certain level and it notifies the source to reduce the rate at

which they send packets.

*Packets produced by TCP will reduce input rate in response to network congestion

*RED is a buffer management technique that attempts to provide equal access to FIFO

system by randomly dropping arriving packets before the buffer overflows.

*A dropped packet provides feedback information to the source and informs the

source to reduce its transmission rate.

*Early drop: discard packets before buffers are full

*Random drop causes some sources to reduce rate before others, causing gradual

reduction in aggregate input rate.

*Minth and Maxth are the two thresholds defined

*RED algorithm uses average queue length, when average queue length is below

Minth , RED does not drop any arriving packets.

*When average queue length is between Minth and Maxth, RED drops an arriving

packet with an increasing probability as the average queue length increases.

*Packet drop probability increases linearly with queue length

*RED improves performance of cooperating TCP sources.

*RED increases loss probability of misbehaving sources

Algorithm:

*Maintain running average of queue length

*If Qavg < minthreshold, do nothing

*If Qavg > maxthreshold, drop packet

*If in between, drop packet according to probability

*Flows that send more packets are more likely to have packets dropped

Packet Drop Profile in RED

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