1. (Modified from Polly Huang’s and last year’s original)
ns-2 Tutorial
Deepak Bansal
15 September, 2000
(Modified from Polly Huang’s and last year’s original)

2. Why ns? Ubiquity of Tcl, C, C++ languages Access to source code
Discrete event simulator
Protocols
TCP, UDP, FTP, HTTP, DSR,
Wired and wireless media
Topology generation
Nam visualization tool
Standard in research community

3. What is ns? ns is a language
object-oriented tcl (otcl) + extensions for building network simulations.
Otcl: object oriented support
tclcl: C++ and otcl linkage
objects
otcl
C++ objects
Base language
Tcl
Give an historical perspective?
You should probably mention nam here or even on the next page.
tclcl ns

4. nam-1

5. ns on Athena Sun workstations
Accessing the course locker:
add 6.899
type “ns” or “nam” at your prompt
/mit/6.899/software/ns-allinone-2.1b6/bin
runs on Linux platforms only (not on Sun!)
on Sun, older version of ns exists in sipbnet.
For more information, see course web page.

6. Tutorial Roadmap Programming in Tcl and Otcl
Creating simulations in ns
Adding new primitives to ns
Tracing

7. Tcl and Otcl Language Basics

8. Basic tcl athena% ns % proc occur {value list} { set count 0
% set a 24
% set b 15
% set c [expr $a + $b]
% set colors {red green blue purple}
% proc occur {value list} {
set count 0
foreach el $list {
if $el == $value {
incr count }
return $count
% set nblues [occur blue $colors]
% puts “I have $nblues blues”
I have 1 blues
Ask who has ever used Tcl? How many people have ever extended the
Tcl interpreter before?
I think, give everything with the interpreter. Then mention that, of course, you could put all of these commands together into a file. Pass them to ns and ns will execute them sequentially.

9. Basic otcl % Class Bagel % Bagel instproc toast {} {
.% set abagel [new Bagel]
_o11
% $abagel info class
Bagel
% Bagel info instances
% Bagel instproc init {args} {
$self instvar toasted_
set toasted_ 0
eval $self next $args }
% Bagel instproc toast {} {
$self instvar toasted_
incr toasted_
if {$toasted>1} then {
error "something's burning!" }
return {}
% $abagel toast
something's burning!
May consider adding another slide to this to illustrate superclasses.

10. Basic ns-2

11. Creating Event Scheduler
Create scheduler
set ns [new Simulator]
Schedule event
$ns at <time> <event>
<event>: any legitimate ns/tcl commands
Start scheduler
$ns run

12. Creating a Network Nodes Links & Queuing set n0 [$ns node]
$ns duplex-link $n0 $n1 <bandwidth> <delay> <queue_type>
<queue_type>: DropTail, RED, CBQ, FQ, SFQ, DRR

13. Creating a simple simulation
# Create a topology
Set ns [new Simulator]
set n0 [$ns node]
set n1 [$ns node]
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
# Add agents
set tcp [$ns create-connection
Agent/TCP $n0 Agent/TCPSink $n1 0]
set ftp [$tcp attach-app FTP]
# Create a schedule
$ns at 0.5 "$ftp start"
$ns at 4.5 "$ftp stop"
#Run the simulation
$ns run
FTP
TCP
FTP
How are you going to fit this whole thing onto one slide? Consider making
one slide for the topology, one time to schedule the events.
TCP
1Mb n0 n1
10ms

14. ns-2 Internal

15. Routing n0 n1 1 1 Addr Classifier Port Classifier classifier_ dmux_
entry_
Addr Classifier
Port Classifier
classifier_
dmux_
entry_ 1 1
Link n0-n1
Link n1-n0

16. Transport n0 n1 1 1 Port Classifier Port Classifier dst_=1.0 dst_=0.0
Addr Classifier
Agent/TCP
Addr Classifier
Agent/TCPSink
agents_
agents_ 1 1
dmux_
dmux_
Link n0-n1
entry_
entry_
classifier_
classifier_
Link n1-n0

17. Application n0 n1 1 1 Port Classifier Application/FTP Port Classifier
dst_=1.0
dst_=0.0
Addr Classifier
Agent/TCP
Addr Classifier
Agent/TCPSink
agents_
agents_ 1 1
dmux_
dmux_
Link n0-n1
entry_
entry_
classifier_
classifier_
Link n1-n0

18. Packet Flow n0 n1 1 1 Port Classifier Application/FTP Port Classifier
dst_=1.0
dst_=0.0
Addr Classifier
Agent/TCP
Addr Classifier
Agent/TCPSink 1 1
Link n0-n1
entry_
entry_
Link n1-n0

19. Extending ns-2 Simulator

20. otcl and C++: The Duality
C++ for data
per packet action
otcl for control
periodic or triggered action

21. Adding New Classes variables procedures New Class otcl New Class
bind()
command()
otcl
TclClass()
New Class
variables
procedures
C++

22. TclClass TclObject Agent Agent/FBI FBIAgent NsObject ?? OTcl C++
mirroring
Static class FBIClass : public TclClass {
public:
FBIClass() : TclClass(“Agent/FBI”) {}
TclObject* create(int, const char*const*) {
return (new FBIAgent()); }
} class_fbi;

23. TclObject: bind() C++ otcl FBIAgent::FBIAgent() { }
bind(“age_”, age_); … }
otcl
Agent/FBI set age_ 10

24. TclObject: command() C++ otcl
Int FBIAgent::command(int argc, const char*const* argv) {
if (argc == 3) {
if (strcomp(argv[1], “mature”) == 0) {
age_ += atoi(argv[2]); …
return(TCL_OK); }
return (Agent::command(argc, argv);
otcl
set mulder [new Agent/FBI]
$mulder mature 20

25. Tracing Trace all packets on all links
$ns trace-all [open out.w w]
<event> <time> <from> <to> <pkt> <size> - - <flowid> <src> <dst> <seqno> <aseqno>
Trace all packets on all links in nam-1 format
$ns namtrace-all [open out.w w]