[e2e] RED parameters

Rahul Verma _97D07016_ rahulv at ee.iitb.ac.in
Mon Dec 10 00:57:19 PST 2001

Hi all,

The recommendations for setting RED paramters at


suggest that
a) max_th should be set to three times min_th and
b) min_th should be set to 5 packets.

However, shouldn't the value of max_th be based on maximum buffer size
too? For example, if the buffer size is large, max_th should also be
large, otherwise it might result in a high packet drop rate. A number of
papers on RED (in the simulation results) mention max_th and min_th
without mentioning the buffer size. Do max_th and min_th make sense if the
buffer size is not specified?

Also as far as reducing the drop rate is concerned, some simple
simulations in ns show that max_th set close to the buffer size gives the
least drop rate. (for example, the default ns settings use B=50 packets,
max_th=15 and min_th=5. Simply changing max_th to 45-50 results in a
drastic improvement in drop rate in a congested scenario.) What is the
motivation behind setting max_th to 15 when the buffer size is 50?

Also, for low buffer sizes, the performance of Drop-Tail is better than
RED in terms of drop rate. What advantage(s) does RED give in such
scenarios? The reduction is average delay might not be significant
compared to the increase in the packet drop rate if RED is used.


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