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[ns] [bug] A bug in nortel DiffServ implementation?
[Bug Report]
-----------------------------
Category: Other
Package: ns ns-allinone-2.1b8a
OS: Linux
Environment Variables:
LD_LIBRARY_PATH=
TCL_LIBRARY=
TK_LIBRARY=
-----------------------------
Description:
Description of Problem:
There seems to be a problem with the idle-flag of the queues which results in a false calculation of the average queuelength in some cases.
How Easily Reproducible:
(e.g. every time, intermittent, once only, etc.)
every time
Steps to Reproduce:
(describe the minimal set of steps necessary to trigger the bug)
1. Run my attached example script ds_bug.tcl to see the result of that bug
2.
3.
Actual Results:
(describe what the application did after performing the above steps)
If a queue is empty (idle-flag is set to 1) and a new packet arrives to the queue, the idle-flag is set in dsredq::enqueue to 0. In the next step it decides if the packet can be queued or has to be dropped. If the packet gets dropped (for example due to an early drop) the queue is still empty but now the idle-flag is set to 0 but it should be 1.
In the attached simulationscript I have the following result of this bug:
I'm simulating some tcp-traffic (FTP) with udp-background (CBR) traffic over an diffserv network. tcp- und udp-traffic are queued to different physical queues at a core-node.
At one point of the simulation the average queuelength of the tcp-queue at the core-node is >= max-threshold so all new arriving packets are dropped and the queuelength decreases down to 0 as packets get dequeued but now new ones enqueued. At the point where the queue is empty (at simulationtime 7.13 seconds) the average queuelength is still quite high and idle-flag is set to 1. Until now everything is as expected.
But then a new tcp-packet arrives after some time (at about 9.09 seconds). In dsredq::enqueue the idle-flag is set to 0, then the packet gets dropped. Now the queue is empty but idle-flag is set to 0.
At 11.07 seconds the next tcp-packet arrives. idle is still 0 but the queue is now already quite a time idle. As idle is 0 the parameter m is set to 0 when calculating the average queuelength. So the (wrong) result of average queuelength calculation is still quite high and packet gets dropped again.
This happens now a number of times. Queuelength is 0 for several seconds but average queuelength stays almost constant over this time (but it should decrease to 0)
The only location where the idle-flag is set to 1 is in dequeue but this gets only executed if there is a packet to be dequeued in the queue.. but there can't be any packets in the queue because they get dropped due to the wrong value in the idle-flag ....
Expected Results:
(describe what the application should have done, were the bug not present)
The idle flag should still be 0 after the packet was dropped when the queuelengt is 0.
Additional Information:
(the following infomation is helpful to debug:
1. simulation script
------ begin of ds_bug.tcl --------
set simulation_time 60
set ns [new Simulator]
set nf [open out.nam w]
$ns namtrace-all $nf
for {set i_ 1} {$i_ < 3} {incr i_} {
set current_tr($i_) [open queuelen-$i_.tr w]
set average_tr($i_) [open average-$i_.tr w]
}
proc finish {} {
global ns nf current_tr average_tr
$ns flush-trace
close $nf
exec nam -a out.nam &
for {set i_ 1} {$i_ < 3} {incr i_} {
close $current_tr($i_)
close $average_tr($i_)
exec xgraph queuelen-$i_.tr average-$i_.tr -geometry 600x450 &
}
exit 0
}
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]
set n5 [$ns node]
set n6 [$ns node]
$ns color 1 Green
$ns color 2 Red
# n0 n5
# \ /
# n2--n3--n4
# / \
# n1 n6
#
$ns duplex-link $n0 $n2 2Mb 15ms DropTail
$ns duplex-link $n1 $n2 2Mb 15ms DropTail
$ns simplex-link $n2 $n3 2Mb 15ms dsRED/edge
$ns simplex-link $n3 $n2 2Mb 15ms dsRED/core
$ns simplex-link $n3 $n4 409600 10ms dsRED/core
$ns simplex-link $n4 $n3 409600 10ms dsRED/edge
$ns duplex-link $n4 $n5 2Mb 60ms DropTail
$ns duplex-link $n4 $n6 409600 60ms DropTail
$ns duplex-link-op $n0 $n2 orient right-down
$ns duplex-link-op $n1 $n2 orient right-up
$ns duplex-link-op $n2 $n3 orient right
$ns duplex-link-op $n3 $n4 orient right
$ns duplex-link-op $n4 $n5 orient right-up
$ns duplex-link-op $n4 $n6 orient right-down
$ns queue-limit $n3 $n4 100
$ns queue-limit $n4 $n5 100
$ns duplex-link-op $n3 $n4 queuePos 0.5
set qE1C [[$ns link $n2 $n3] queue]
set qE2C [[$ns link $n4 $n3] queue]
set qCE1 [[$ns link $n3 $n2] queue]
set qCE2 [[$ns link $n3 $n4] queue]
$qE1C meanPktSize 1000
$qE1C set numQueues_ 3
$qE1C setNumPrec 3
$qE1C setSchedularMode RR
$qE1C setMREDMode RIO-C
$qE1C addPolicyEntry [$n0 id] -1 TokenBucket 18 5000000 4000
$qE1C addPolicyEntry [$n1 id] -1 TokenBucket 26 5000000 4000
$qE1C addPolicerEntry TokenBucket 18 20
$qE1C addPolicerEntry TokenBucket 26 28
$qE1C addPHBEntry 18 1 0
$qE1C addPHBEntry 20 1 1
$qE1C addPHBEntry 26 2 0
$qE1C addPHBEntry 28 2 1
$qE1C configQ 0 0 8 16 0.02
$qE1C configQ 0 1 4 8 0.10
$qE1C configQ 0 2 2 4 0.50
$qE1C configQ 1 0 8 16 0.02
$qE1C configQ 1 1 4 8 0.10
$qE1C configQ 1 2 2 4 0.50
$qE1C configQ 2 0 8 16 0.02
$qE1C configQ 2 1 4 8 0.10
$qE1C configQ 2 2 2 4 0.50
$qE2C meanPktSize 1000
$qE2C set numQueues_ 3
$qE2C setNumPrec 3
$qE2C setSchedularMode RR
$qE2C setMREDMode RIO-C
$qE2C addPolicyEntry -1 [$n0 id] TokenBucket 18 5000000 4000
$qE2C addPolicyEntry -1 [$n1 id] TokenBucket 26 5000000 4000
$qE2C addPolicerEntry TokenBucket 18 20
$qE2C addPolicerEntry TokenBucket 26 28
$qE2C addPHBEntry 18 1 0
$qE2C addPHBEntry 20 1 1
$qE2C addPHBEntry 26 2 0
$qE2C addPHBEntry 28 2 1
$qE2C configQ 0 0 8 16 0.02
$qE2C configQ 0 1 4 8 0.10
$qE2C configQ 0 2 2 4 0.50
$qE2C configQ 1 0 8 16 0.02
$qE2C configQ 1 1 4 8 0.10
$qE2C configQ 1 2 2 4 0.50
$qE2C configQ 2 0 8 16 0.02
$qE2C configQ 2 1 4 8 0.10
$qE2C configQ 2 2 2 4 0.50
$qCE1 meanPktSize 1000
$qCE1 set numQueues_ 3
$qCE1 setNumPrec 3
$qCE1 setSchedularMode RR
$qCE1 setMREDMode RIO-C
$qCE1 addPHBEntry 18 1 0
$qCE1 addPHBEntry 20 1 1
$qCE1 addPHBEntry 22 1 2
$qCE1 addPHBEntry 26 2 0
$qCE1 addPHBEntry 28 2 1
$qCE1 addPHBEntry 30 2 2
$qCE1 configQ 0 0 8 16 0.02
$qCE1 configQ 0 1 4 8 0.10
$qCE1 configQ 0 2 2 4 0.50
$qCE1 configQ 1 0 8 16 0.02
$qCE1 configQ 1 1 4 8 0.10
$qCE1 configQ 1 2 2 4 0.50
$qCE1 configQ 2 0 8 16 0.02
$qCE1 configQ 2 1 4 8 0.10
$qCE1 configQ 2 2 2 4 0.50
$qCE2 debugmessages 0 0
$qCE2 debugmessages 1 0
$qCE2 debugmessages 2 1
$qCE2 meanPktSize 1000
$qCE2 set numQueues_ 3
$qCE2 setNumPrec 3
$qCE2 setSchedularMode RR
$qCE2 setMREDMode RIO-D
$qCE2 addPHBEntry 18 1 0
$qCE2 addPHBEntry 20 1 1
$qCE2 addPHBEntry 22 1 2
$qCE2 addPHBEntry 26 2 0
$qCE2 addPHBEntry 28 2 1
$qCE2 addPHBEntry 30 2 2
$qCE2 configQ 0 0 8 16 0.01
$qCE2 configQ 0 1 4 8 0.02
$qCE2 configQ 0 2 2 4 0.05
$qCE2 configQ 1 0 16 32 0.01
$qCE2 configQ 1 1 8 16 0.02
$qCE2 configQ 1 2 4 8 0.04
$qCE2 configQ 2 0 4 12 0.01
$qCE2 configQ 2 1 4 8 0.02
$qCE2 configQ 2 2 2 4 0.04
for {set s_count 0} {$s_count < 4} {incr s_count} {
set tcp($s_count) [new Agent/TCP/Reno]
$tcp($s_count) set class_ 2
$ns attach-agent $n1 $tcp($s_count)
set ftp($s_count) [new Application/FTP]
$ftp($s_count) attach-agent $tcp($s_count)
set sink($s_count) [new Agent/TCPSink]
$ns attach-agent $n6 $sink($s_count)
$ns connect $tcp($s_count) $sink($s_count)
$tcp($s_count) set packetSize_ 1000
}
set udp0 [new Agent/UDP]
$udp0 set class_ 1
set cbr0 [new Application/Traffic/CBR]
$ns attach-agent $n0 $udp0
$cbr0 attach-agent $udp0
$cbr0 set packetSize_ 1000
$cbr0 set rate_ 320000
set null0 [new Agent/LossMonitor]
$ns attach-agent $n5 $null0
$ns connect $udp0 $null0
proc ds_stats {} {
global qE1C qCE1 qE2C qCE2
puts "\n\n**** edge1 -> core ****"
$qE1C printStats
puts "\n\n**** core -> edge2 ****"
$qCE2 printStats
puts "\n\n**** edge2 -> core ****"
$qE2C printStats
puts "\n\n**** core -> edge1 ****"
$qCE1 printStats
}
proc queue_stats {queue} {
global current_tr average_tr
set time 0.1
set ns [Simulator instance]
set now [$ns now]
for {set i_ 1} {$i_ < 3} {incr i_} {
set current_ [$queue getCurrent $i_]
set average_ [$queue getAverage $i_]
puts $current_tr($i_) "$now $current_"
puts $average_tr($i_) "$now $average_"
}
$ns at [expr $now+$time] "queue_stats $queue"
}
for {set s_count 0} {$s_count < 4} {incr s_count} {
$ns at 0.$s_count "$ftp($s_count) start"
$ns at $simulation_time "$ftp($s_count) stop"
}
$ns at 0.0 "$cbr0 start"
$ns at 0.0 "queue_stats $qCE2"
$ns at $simulation_time "$cbr0 stop"
$ns at [expr $simulation_time + 5] "ds_stats"
$ns at [expr $simulation_time + 5] "finish"
$ns run
------ end of ds_bug.tcl ------