1. Karthik Sadasivam Banuprasad Samudrala
ns-2 tutorial
CSCI 5931 Network Security
Instructor : Dr. T. Andrew Yang
Karthik Sadasivam
Banuprasad Samudrala

2. Introduction
Ns-2 is a discrete event simulator targeted at network research
focused on modeling network protocols
wired, wireless, satellite
TCP, UDP, multicast, unicast
web, telnet, ftp
ad hoc routing, sensor networks
infrastructure: stats, tracing, error models, etc

3. Goals of ns support networking research and education
protocol design, traffic studies, etc.
protocol comparison
provide a collaborative environment
freely distributed, open source
share code, protocols, models, etc.
allow easy comparision of similar protocols
increase confidence in results
models provide useful results in several situations
multiple levels of detail in one simulator

4. ns status platforms: basically all Unix and Windows
size: about 200k loc each C++ and Tcl, 350 page manual
user-base: >1k institutions, >10k users
releases about every 6 months, plus daily snapshots

5. Components of ns ns, the simulator itself nam, the Network AniMator
visualize ns (or other) output
GUI input simple ns scenarios
pre-processing:
traffic and topology generators
post-processing:
simple trace analysis, often in Awk, Perl, or Tcl

6. ns Software Structure: C++ and Otcl
Uses two languages
C++ for packet-processing
fast to run, detailed, complete control
OTcl for control
simulation setup, configuration, occasional actions
fast to write and change
pros: trade-off running vs. writing speed, powerful/documented config language
cons: two languages to learn and debug in

7. oTcl and C++: The Duality
OTcl (object variant of Tcl) and C++ share class hierarchy
TclCL is glue library that makes it easy to share functions, variables, etc.

8. Installation and documentation
download ns-allinone
includes Tcl, OTcl, TclCL, ns, nam, etc.
mailing list:
documentation (see url above)
Marc Gries tutorial
ns manual

9. Steps to set up the simulation
Initialize the simulator
Define files for output (tracing)
Set up the topology
Set up the “agents”
Set up the traffic between the nodes
Start the simulation
Analyze the trace files to compute the parameters of interest

10. Example : TCP n0 n1 set ns [new Simulator] set n0 [$ns node]
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ns at 0.2 "$ftp start"
$ns at 1.2 ”exit"
$ns run
$ns duplex-link $n0 $n1 1.5Mb 10ms DropTail
set tcp [new Agent/TCP]
set tcpsink [new Agent/TCPSink]
$ns attach-agent $n0 $tcp
$ns attach-agent $n1 $tcpsink
$ns connect $tcp $tcpsink

11. Script to start nam set nf [open out.nam w] $ns namtrace-all $nf
proc finish {} {
global ns nf
$ns flush-trace
close $nf
exec nam out.nam &
exit 0 }
# your code goes in here
$ns at 12.0 "finish" # 12.0 is the simulation time in secs

12. Screenshots
Project B.2
Project B.1

13. References
[1] slides by John Heidemann
[2] ns2 website:
[3] ns-2 Tutorial:
[4] Tcl/Tk tutorial :