NS2 First Report
Submitters:
Stella Pantofel
Michael Halperin
Igor Berman
Simulation of
Explicit Congestion
Notification(ECN)
and
Random Early Detection(RED)
With TCP Reno and TCP Sack
The outline of the project
Using NS-2 simulator, we simulate a congested network that uses
RED with ECN with following options:
–
–
–
–
TCP Reno / TCP SACK
Different RED threshold parameters .
Variable number of connections.
The network will have usual links and a satellite link.
We will supply results (graphs) that compare the throughput and
the congestion window behavior.
Example Topologies :
The main idea of any chosen topology is to create a bottle
neck in order to simulate the congestion problem.
In the 1st case the link zero-one is the bottle neck of the
topology. In the 2nd case the link two-three is the bottle neck.
Description of NS2
options using Tcl
• Defining variables/constants:
– set NodeNumber 10
• Comments:
–
# this is comment
• New instance of simulator:
– set ns [new Simulator]
• New node:
– set N [$ns node]
• New link: $ns <kind of link> <src> <dst>
<bandwidth><delay><kind of queue>
– Example: set link [$ns simplex-link $N $D 2Mb 1ms RED]
Ns2 options continue…
• New protocol agent:
– set tcpAgent [new Agent/TCP/Newreno]
– set tcpAgetn [new Agent/TCP/Sack1]
• Attaching to node some agent
– $ns attach-agent $n0 $tcpAgent
• And sink agent
– set sink [new Agent/TCPSink/DelAck]
– set sink [new Agent/TCPSink/Sack1]
– $ns attach-agent $n4 $sink
• Connecting tcp and sink agents:
– $ns connect $tcp $sink
Parameters to Tcp Agent
• Size of window:
– $tcp set window_ 8000
• Size of packet
– $tcp set packetSize_ 552
• Flow id:
– $tcp set fid_ $k
• Ecn option:
– $tcp set ecn_ 1
Creating new application
over Tcp agent
• Creation:
– set ftp [new Application/FTP]
• Attaching:
– $ftp attach-agent $tcp
• Type:
– $ftp set type_ FTP
Scheduling Events
In format of: $ns2 at <time> <event>
• Examples:
– $ns at 0.1 "$ftp start“
– $ns at 124.0 "$ftp stop“
• And at the end:
– $ns run
Red Queue
Parameters:
• Queue/RED set thresh_ 5
• Queue/RED set maxthresh_ 15
• Queue/RED set q_weight_ 0.002
Remark:
Parameters should be set, before defining new instance of
queue.
ECN options
• Red queue marks messages rather than
throws them away:
– Queue/RED set setbit_ true : turning option on
– $redq set setbit_ true : defining particular queue
• Tcp agent have to support ecn option:
– Agent/TCP set old_ecn_ 1 : turning option on
– $tcpAgent set ecn_ 1 : defining particular agent
Error model over the link
• Creation of loss module:
– set loss_module [new ErrorModel]
• Rate of loosing packets:
– $loss_module set rate_ 0.2
• Loss module uses random generator of uniformly
distributed random variable:
– $loss_module ranvar [new RandomVariable/Uniform]
• Where go lost packets to:
– $loss_module drop-target [new Agent/Null]
• Connecting loss model with link between 2 nodes:
– $ns lossmodel $loss_module $n2 $n3
Random variables and their uses
• Uses:
– Delays between connections.
– Delays of the links.
– Size of data.
• Example:
– Delays between connections are distributed
exponentially:
Random variables and
their uses continue…
• Define generator for random variable:
– set rng [new RNG]
• Define seed to generator (if 0 generates each time new
sequence of values.
– $rng2 seed 2
• Define new random variable and parameters to it:
– set RV [new RandomVariable/Exponential]
– $RV set avg_ 0.3
– $RV use-rng $rng1
• Use:
– set t [expr $t + [$RV value]]
– $tcp set starts $t
Traces of the simulation
• Simulator allows to get information about the events
registered in the network.
• Example:
– $ns trace-all <filename>
• The output file will contain following data:
<event><time><source><destination><flags>
and more…
• By using these files as input to different scripts we can
calculate desired statistics.
– Example: throughput per time unit on any specified link.
Congestion Window Behavior
• Each time unit we sample the window size
of the given TCP connection.
– The command we use in order to sample:
• $tcp set cwnd_
• Cwnd_ is the current window size of the TCP
connection
• The result is recorded in a special file.
• Later on this file is processed and a graph is
created from its data