[ns] effective ENC implementation in NS-2

["Joshua Mentz" <jmentz@cs.uct.ac.za>]

I have spent the whole of today trying to implement ECN effectively but have encountered the following problems:

 

*Firstly, I have had difficulty finding appropriate values for thresh_ , maxthresh_ and q_weight.  In general I have used defaults or made educated guesses.

 

*Looking at the RED queue trace reveals that the E flag (congestion experienced) is seldom set.

 

*In addition to that, there are no instances of the C flag (ECN echo) being set during congestion.  It is only set during the TCP initialization.

 

*Enabling the setbit_ option doesn't result in reduced packet losses. Fairness is very low.

 

I would be grateful for any pointers.

 

Thank you                               

Joshua Mentz

Following is my tcl script:

 

#Create a simulator object
set ns [new Simulator]

 

#Define different colors for data flows (for NAM)
$ns color 1 Blue
$ns color 2 Red
$ns color 3 green

 

#Open the NAM trace file   
set nf [open sim1.nam w]
$ns namtrace-all $nf

 

#--------------Define a 'finish' procedure---------------------
proc finish {} {
        global ns nf f
        $ns flush-trace
        #Close the NAM trace file
        close $f
 close $nf
        #Execute NAM on the trace file
        exec nam.exe sim1.nam &  
        exit 0    
}

 

#Create four nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]

 

#-----------CLASS VARIABLE MODIFICATIONS---------------------------
#modify agent class vairables
Agent/TCP/Sack1 set window_ 100       
Agent/TCP/Sack1 set packetSize_ 1500   
Agent/TCP/Sack1 set ecn_ true 
      
Application/Traffic/Pareto set rate_ 1mb

 

Queue/RED set setbit_ true
#Queue/RED set thresh_ 2
#Queue/RED set maxthresh_ 8
#Queue/RED set q_weight_ 0.002

 

#Create links between the nodes
$ns duplex-link $n0 $n3 10Mb 1ms DropTail
$ns duplex-link $n1 $n3 10Mb 1ms DropTail
$ns duplex-link $n2 $n3 10Mb 1ms DropTail
$ns duplex-link $n3 $n4 20Mb 5ms RED
  
#Set Queue Size of link (n4-n5) to 10 packets
$ns queue-limit $n3 $n4 20

 

set f [open sim1Q.tr w]
$ns trace-queue $n3 $n4 $f

 

#Give node position (for NAM)
$ns duplex-link-op $n0 $n3 orient right-down
$ns duplex-link-op $n1 $n3 orient right
$ns duplex-link-op $n2 $n3 orient right-up
$ns duplex-link-op $n3 $n4 orient right

 

#Monitor the queue for link (n4-n5). (for NAM)
$ns duplex-link-op $n3 $n4 queuePos 0.5

 

#---------TCP connection 0-------------------------------
set tcp0 [new Agent/TCP/Sack1]
$tcp0 set class_ 2    
$ns attach-agent $n0 $tcp0

 

set sink [new Agent/TCPSink/Sack1]
$ns attach-agent $n4 $sink
$ns connect $tcp0 $sink
$tcp0 set fid_ 0

 

set cbr0 [new Application/Traffic/Pareto]
$cbr0 attach-agent $tcp0

 

#---------TCP connection 1-------------------------------
set tcp1 [new Agent/TCP/Sack1]   
$ns attach-agent $n1 $tcp1

 

set sink [new Agent/TCPSink/Sack1]
$ns attach-agent $n4 $sink
$ns connect $tcp1 $sink
$tcp1 set fid_ 1

 

set cbr1 [new Application/Traffic/Pareto]
$cbr1 attach-agent $tcp1

 

#---------TCP connection 2-------------------------------
set tcp2 [new Agent/TCP/Sack1]   
$ns attach-agent $n2 $tcp2

 

set sink [new Agent/TCPSink/Sack1]
$ns attach-agent $n4 $sink
$ns connect $tcp2 $sink
$tcp2 set fid_ 2

 

set cbr2 [new Application/Traffic/Pareto]
$cbr2 attach-agent $tcp2

 

#-----------------Schedule events----------------------------

 

$ns at 0.0 "$cbr0 start"
$ns at 0.0 "$cbr1 start"
$ns at 0.0 "$cbr2 start"
$ns at 1.0 "$cbr0 stop"
$ns at 1.0 "$cbr1 stop"
$ns at 1.0 "$cbr2 stop"

 

$ns at 1.2 "finish"

 

#Print CBR packet size and interval
#puts "CBR packet size = [$cbr0 set packet_size_]"
#puts "CBR interval = [$cbr0 set interval_]"

 

#Run the simulation
$ns run