RED dropping packets bug?
Wed, 29 Oct 1997 11:52:25 PST
>There is something odd with packets dropping behavior for RED and
>If I change the 800Kb link of net0 (test-suite.tcl) from DropTail to
>RED and compare the xgraph output, the DropTail packet lost at time
>1.9 does not appear for RED. With other words, DropTail drop a
>packet because of queue overflow, but there is no such queue
>overflow for RED, which doesn't make any sense.
Thanks for the report. I just checked it out, and it turns out
that DropTail and RED count queues differently, and are off by one,
relative to each other -
$ns duplex-link $node_(r1) $node_(k1) 800Kb 100ms DropTail
$ns queue-limit $node_(r1) $node_(k1) 6
gives the same behavior as
$ns duplex-link $node_(r1) $node_(k1) 800Kb 100ms RED
$ns queue-limit $node_(r1) $node_(k1) 5
for this simulation.
Clearly we should standardize on whether we do or do not count the
packet currently being transmitted as a member of the queue, so that
DropTail and RED are in sync about queue sizes...