NS-2 is a discrete event network simulator for modelling network protocols and traffic. It models packets, links, queues and supports protocols like TCP and IP. NS-2 allows simulation of different network scenarios and is widely used for networking research. Simulations are created using OTcl scripts which interface with the C++-based simulator core. The document provides an overview of NS-2 architecture, usage and programming and includes an example simulation script.

1. 1
NS--2 IntroductionIntroduction
byby
Venkatamangarao NampallyVenkatamangarao Nampally
KattangurKattangur

2. 2
OutlineOutline
• BackgroundBackground
• ArchitectureArchitecture
• UsageUsage
• SimulationSimulation
• NS-programmingNS-programming
• ExampleExample
• SummarySummary

3. 3
ns-2, the Network Simulatorns-2, the Network Simulator
• AA discrete event simulatordiscrete event simulator modellingmodelling
network protocolsnetwork protocols
– Packets, links, queues, protocolsPackets, links, queues, protocols
– Visualizer (Visualizer (NAMNAM))
– Trace playbackTrace playback
– Error modelsError models
• Targeted at networking researchTargeted at networking research
• Supports for all types of simulationsSupports for all types of simulations

4. 4
HistoryHistory
• 1989:1989: REALREAL by Keshavby Keshav
• 1995:1995: nsns by Floyd, McCanne at LBLby Floyd, McCanne at LBL
• 1997:1997: ns-2ns-2 by the VINT projectby the VINT project
((Virtual InterNetwork TestbedVirtual InterNetwork Testbed) at) at
LBL, Xerox PARC, UCB, USC/ISILBL, Xerox PARC, UCB, USC/ISI
• 1999: Wireless models added @ CMU1999: Wireless models added @ CMU
• Now:Now: ns-2.29ns-2.29 maintained at USC/ISImaintained at USC/ISI
– ns-2.30ns-2.30 pending releasepending release

5. NS-2 OverviewNS-2 Overview
• TCP/IP NS2 OSI 7-LayerTCP/IP NS2 OSI 7-Layer
5
•Application
•Presentation
•Session
•Transport
•Network
•Data Link
•Physical
•Application
•Agent
•Node
•Link
•Application
•TCP/UDP
•IP
•Network
•Access

6. Platforms SupportedPlatforms Supported
• Most UNIX and UNIX-like systemsMost UNIX and UNIX-like systems
 FreeBSDFreeBSD
 LinuxLinux
 SolarisSolaris
• Windows 98/2000/2003/XPWindows 98/2000/2003/XP
– Cygwin requiredCygwin required
– Some work , some doesntSome work , some doesnt
6

7. User’s PerspectiveUser’s Perspective
• From the user’s perspective, NS−2 isFrom the user’s perspective, NS−2 is
an OTcl interpreter that takes an OTclan OTcl interpreter that takes an OTcl
script as input and produces a tracescript as input and produces a trace
file as output.file as output.
7

8. 8
NS-2 EnvironmentNS-2 Environment
•Simulation
Scenario
•Tcl Script
•C++
Implementation
•1 •2
•set ns_ [new Simulator]
•set node_(0) [$ns_ node]
•set node_(1) [$ns_ node]
•class MobileNode : public Node
•{
• friend class PositionHandler;
•public:
• MobileNode();
• •
• •
•}

9. 9
ComponentsComponents
• ns-2ns-2, the simulator itself, the simulator itself
– Specify simulation, generate tracesSpecify simulation, generate traces
– Depends on Tcl/Tk, OTcl, TclCLDepends on Tcl/Tk, OTcl, TclCL
• namnam, the network animator, the network animator
– Animate traces from simulationAnimate traces from simulation
– GUI for constructing simple simulationsGUI for constructing simple simulations
• Pre-processingPre-processing
– Traffic, topology generationTraffic, topology generation
• Post-processingPost-processing
– Analyse trace output withAnalyse trace output with awkawk, etc, etc

10. NS ModelsNS Models
• Traffic models and applications:Traffic models and applications:
– Web, FTP, telnet, constant-bit rateWeb, FTP, telnet, constant-bit rate
• Transport protocols:Transport protocols:
– unicast: TCP (Reno, Vegas, etc.), UDPunicast: TCP (Reno, Vegas, etc.), UDP
– Multicast: SRMMulticast: SRM
• Routing and queueing:Routing and queueing:
– Wired routing, ad hoc rtgWired routing, ad hoc rtg
– queueing protocols: RED, drop-tail, etcqueueing protocols: RED, drop-tail, etc
• Physical media:Physical media:
– Wired (point-to-point, LANs), wirelessWired (point-to-point, LANs), wireless
(multiple propagation models), satellite(multiple propagation models), satellite
10

11. Basic ArchitectureBasic Architecture
11
•An executable command ns
•Input: tcl simulation scripting file
•Output: trace file  Animation by NAM or
plotting graph by Xgraph (gunplot)

12. NS2-GoalsNS2-Goals
To support networking research andTo support networking research and
educationeducation
–– Protocol design, traffic studies, etc.Protocol design, traffic studies, etc.
–– Protocol comparison;Protocol comparison;
–– New architecture designs are alsoNew architecture designs are also
supported.supported.
•• To provideTo provide collaborativecollaborative environmentenvironment
–– Freely distributed, open source;Freely distributed, open source;
–– Increase confidenceIncrease confidence in resultin result
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13. 13
UsingUsing nsns
Simulation
model
Define
problem
Post-process
results
Execute
simulation
Extend
simulator

14. 14
UsingUsing nsns
• Create simulationCreate simulation
– Describe network, protocols, sources, sinksDescribe network, protocols, sources, sinks
– Interface via OTcl which controls C++Interface via OTcl which controls C++
• Execute simulationExecute simulation
– Simulator maintains event list (packet list), executesSimulator maintains event list (packet list), executes
next event (packet), repeats until donenext event (packet), repeats until done
– Events happen instantly inEvents happen instantly in virtual timevirtual time but could takebut could take
arbitrarily longarbitrarily long real timereal time
– Single thread of control, no locking, races, etcSingle thread of control, no locking, races, etc
• Post-process resultsPost-process results
– Scripts (awk, perl, python) to process text outputScripts (awk, perl, python) to process text output
– No standard library but some available on webNo standard library but some available on web

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LanguagesLanguages
• C++ forC++ for datadata
– Per-packet processing, the core ofPer-packet processing, the core of nsns
– Fast to run, detailed, complete controlFast to run, detailed, complete control
• OTcl forOTcl for controlcontrol
– Simulation descriptionSimulation description
– Periodic or triggered actionsPeriodic or triggered actions
– Manipulating existing C++ objectsManipulating existing C++ objects
– Faster to write and change codeFaster to write and change code
» (a matter of opinion)(a matter of opinion)

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Basic TclBasic Tcl
# Variables:# Variables:
setset x 10x 10
setset xx
putsputs “x is $x”“x is $x”
# Functions and expressions:# Functions and expressions:
setset y [pow x 2]y [pow x 2]
setset y [expr x*x]y [expr x*x]
# Control flow:# Control flow:
ifif {$x > 0} {{$x > 0} { returnreturn $x }$x } elseelse {{
returnreturn [expr -$x] }[expr -$x] }
whilewhile { $x > 0 } {{ $x > 0 } {
putsputs $x$x
incrincr x –1x –1
}}
forfor {{setset i 0} {$i<10} {i 0} {$i<10} {incrincr i} {i} {
putsputs “$i == $i”“$i == $i”
}}
# Procedures:# Procedures:
procproc pow {x n} {pow {x n} {
ifif {$n == 1} {{$n == 1} { returnreturn $x }$x }
setset part [part [powpow x [x [exprexpr $n-1]]$n-1]]
returnreturn [[exprexpr $x*$part]$x*$part]
}}
# Files:# Files:
setset file [file [open “open “nstrace.txt” w]nstrace.txt” w]
setset line [line [getsgets $file]$file]
puts –nonewlineputs –nonewline $file “hello!”$file “hello!”
closeclose $file$file

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App1
Agent1
App2
Agent2
Node
From Network to SimulationFrom Network to Simulation
Application,
Agent & Node
LinkNode
App1
Agent1
App2
Agent2
Node
App1
Agent1
App2
Agent2
Node
App1
Agent1
App2
Agent2
Node
Node Node Node
Link
Link
Link Link
Link
Link
Link
Link
App1
Agent1
App2
Agent2
Node
App1
Agent1
App2
Agent2
Node

18. Visualization ToolsVisualization Tools
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•nam-1 (Network AniMator Version 1)
•Packet-level animation
•Well supported by ns
•xgraph
•Simulation results

19. NAMNAM
19

20. Elements for NS-2 simulationElements for NS-2 simulation
20
•Create the event scheduler
•Turn on tracing
•Create network
•Setup routing
•Create transport connection
•Create traffic
•Transmit application-level data

21. Creating Simulation environmentCreating Simulation environment
21
 Create event scheduler
 set ns [new Simulator]
 Schedule events
 $ns at <time> <event>
 <event>: any legitimate ns/tcl commands
 Start scheduler
 $ns run

22. TracingTracing
22
 Turn on tracing on specific links
 $ns trace-queue $n0 $n1
 $ns namtrace-queue $n0 $n1

23. Creating nodes, links and queuesCreating nodes, links and queues
23
 Nodes
 set n0 [$ns node]
 set n1 [$ns node]
 Links and queuing
 $ns duplex-link $n0 $n1 <bandwidth> <delay>
<queue_type>
 <queue_type>: DropTail, RED, CBQ, FQ, SFQ,
DRR

24. Creating connection :UDPCreating connection :UDP
24
 UDP
 set udp [new Agent/UDP]
 set null [new Agent/Null]
 $ns attach-agent $n0 $udp
 $ns attach-agent $n1 $null
 $ns connect $udp $null

25. Creating Traffic : on top of UDPCreating Traffic : on top of UDP
25
 CBR
 set src [new
Application/Traffic/CBR]

26. Creating connection : TCPCreating connection : TCP
26
 TCP
 set tcp [new Agent/TCP]
 set tcpsink [new Agent/TCPSink]
 $ns attach-agent $n0 $tcp
 $ns attach-agent $n1 $tcpsink
 $ns connect $tcp $tcpsink

27. Creating Traffic : on top of TCPCreating Traffic : on top of TCP
27
 FTP
 set ftp [new Application/FTP]
 $ftp attach-agent $tcp
 Telnet
 set telnet [new
Application/Telnet]
 $telnet attach-agent $tcp

28. Simple Simulation ExampleSimple Simulation Example
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•This network consists of 4 nodes (n0, n1, n2, n3)
•The duplex links between n0 and n2, and n1 and n2 have
•The duplex link between n2 and n3 has 1.7 Mbps of bandwidth and 20 ms of
delay 2 Mbps of bandwidth and 10 ms of delay.
•Each node uses a DropTail queue,of which the maximum size is 10
•ftp session is based on tcp
•tcp agent: generate packet (l=1k bytes)
•sink: generate ack and free packets
•cbr session is based on udp
•udp agent: generate packet (l=1k bytes)
@ 1 Mbps
•null: free packets

29. Script structureScript structure
29
# parameters and options
set ns [new Simulator]
# [Turn on tracing]
# Create topology
# Setup packet loss, link dynamics
# Create routing agents
# Create:
# - protocol agents
# - application and/or setup traffic sources
# Post-processing procs
# Start simulation

30. Final Topology Generated (final screenshot)Final Topology Generated (final screenshot)
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31. 31
SummarySummary
• BackgroundBackground
• ArchitectureArchitecture
• UsageUsage
• SimulationSimulation
• NS-programmingNS-programming
• ExampleExample
• SummarySummary

32. 32
Thank You!Thank You!