802.11 Simulations Using ns2

Evan Jones

ejones@uwaterloo.ca

What can I do with ns2?

• Wired network simulations
• Wireless network simulations
• Includes common protocols (TCP, RealAudio, etc)
• Many low level details are configurable (queuing policy, MAC protocol, etc)

High Level Structure

• Library of C objects with TCL interfaces
  • Nodes
  • Routing Protocols
  • Application Protocols
  • etc.
• Connect the objects together via TCL

Workflow

1. (Optional) Create custom ns2 object
2. Create TCL scenario file
3. Run the scenario to produce a trace file
4. Process the trace file to get results

Basic Wireless Scenario

simple.tcl [view] [download]:

• Chain of 5 nodes, spaced 200m apart
• Use DSDV routing
• FTP transfer from one end to the other
• Want to measure the throughput

Diagram

Options

# ===============
# Define options
# ===============
set val(chan)         Channel/WirelessChannel  ;# channel type
set val(prop)         Propagation/TwoRayGround ;# radio-propagation model
set val(ant)          Antenna/OmniAntenna      ;# Antenna type
set val(ll)           LL                       ;# Link layer type
set val(ifq)          Queue/DropTail/PriQueue  ;# Interface queue type
set val(ifqlen)       50                       ;# max packet in ifq
set val(netif)        Phy/WirelessPhy          ;# network interface type
set val(mac)          Mac/802_11               ;# MAC type
set val(rp)           DSDV                     ;# ad-hoc routing protocol  
set val(nn)           5                        ;# number of mobilenodes

Set Up Simulator

# Create simulator
set ns_    [new Simulator]

# Set up trace file
$ns_ use-newtrace
set tracefd [open simple.tr w]
$ns_ trace-all $tracefd

# Create the "general operations director"
# Used internally by MAC layer: must create!
create-god $val(nn)

# Create and configure topography (used for mobile scenarios)
set topo [new Topography]
# 1000x1000m terrain
$topo load_flatgrid 1000 1000

Configure Nodes

$ns_ node-config -adhocRouting $val(rp) \
        -llType $val(ll) \
        -macType $val(mac) \
        -ifqType $val(ifq) \
        -ifqLen $val(ifqlen) \
        -antType $val(ant) \
        -propType $val(prop) \
        -phyType $val(netif) \
        -channel [new $val(chan)] \
        -topoInstance $topo \
        -agentTrace ON \
        -routerTrace ON \
        -macTrace OFF \
        -movementTrace OFF

Create Nodes

for {set i 0} {$i < $val(nn) } {incr i} {
        set node_($i) [$ns_ node]       
        $node_($i) random-motion 0              ;# disable random motion
        $node_($i) set X_ 0.0
        $node_($i) set Y_ 0.0
        $node_($i) set Z_ 0.0
}

$node_(0) set X_ 0.0
$node_(1) set X_ 200.0
$node_(2) set X_ 400.0
$node_(3) set X_ 600.0
$node_(4) set X_ 800.0

Source and Destination

# 1500 - 20 byte IP header - 40 byte TCP header = 1440 bytes
Agent/TCP set packetSize_ 1440 ;# This size EXCLUDES the TCP header

set agent [new Agent/TCP]
set app [new Application/FTP]
set sink [new Agent/TCPSink]

$app attach-agent $agent

$ns_ attach-agent $node_(0) $agent
$ns_ attach-agent $node_(4) $sink
$ns_ connect $agent $sink

Node Structure

Run It

# 120 seconds of running the simulation time
$ns_ at 0.0 "$app start"
$ns_ at 120.0 "$ns_ halt"
$ns_ run

$ns_ flush-trace
close $tracefd

Trace File

s -t 0.000000000 -Hs 0 -Hd -2 -Ni 0 -Nx 0.00 -Ny 0.00 -Nz 0.00 -Ne -1.000000 -Nl AGT …
r -t 0.000000000 -Hs 0 -Hd -2 -Ni 0 -Nx 0.00 -Ny 0.00 -Nz 0.00 -Ne -1.000000 -Nl RTR …

• Each line represents a message being transferred
• Common fields:
  • Event type (s = send, r = received, d = drop)
  • Time stamp
  • Source and destination
  • XYZ co-ordinates of the node
  • Network layer (AGT = agent, RTR = router, …)
  • … many many others

Miscellaneous Tools

• Both command line tools and a Python API [details]
• ns2stats.py: Aggregate statistics
• throughputOverTime.py: Throughput per second
• stupidplot.py: Plot data from Python

Throughput Over Time Output

Time    0:0 -> 4:0      4:0 -> 0:0
1.0     0.0     0.0
2.0     0.0     0.0
3.0     0.0     0.0
4.0     0.0     0.0
5.0     0.0     0.0
6.0     0.0     0.0
7.0     0.0     0.0
8.0     0.0     0.0
9.0     0.0     0.0
10.0    0.0     0.0

Stick it in GnuPlot

if len( sys.argv ) != 3:
        print "example.py <trace file> <output eps file>"
        sys.exit( 1 )

input = file( sys.argv[1] )
flows = flowanalysis.parseFlowsFromTrace( input )
input.close()

data = throughputOverTime.throughputOverTime( flows )

stupidplot.gnuplotTable( data, sys.argv[2] )

Results

Random Tips and Tricks

• Automate everything
• Use command line parameters to customize scenario
• Read the trace files to understand what is happening
• GnuPlot sucks, but its the best thing available

Resources

http://evanjones.ca/ns2.html

Includes:

• This presentation
• The sample scripts used in this presentation
• The Python tools
• Links to other ns2 resources (tutorials, documentation, etc.)

Questions?