1. Wireless Communication : LAB 3
Background of Wireless Communication
Wireless Communication Technology
Wireless Networking and Mobile IP
Wireless Local Area Networks
Student Presentations and Projects
Introduction to NS2 Programming

2. Outline NS overview NS structure and basics
Steps to create a typical NS script
Summary: Generic Script Structure
Vis Tools
Useful pointers
NS by Example (
Where is documentation and Tutorials:

3. What is NS Discrete event simulator targeted for networking research
Discrete event simulation:
representing a system by a collection of states and a set of events that describe state changes.
Discrete-Event/Continuous-Time
An event in NS
a packet ID that is unique for a packet with scheduled time and the pointer to an network object that handles the packet

4. What can ns simulate? Topology: wired, wireless
Queue Scheduling Algorithms: RED, DropTail, …
Transport Protocols: TCP (all flavors), UDP, …
Routing: Static and dynamic routing, MPLS, …
Application: FTP, HTTP, Telnet, Traffic generators, …
Multicast
Various error models for link failures
Open source

5. NS Structure NS is written in oTcl and C++;
Efficiency and simplicity
oTcl is an extension to oTcl (object Tcl):
Have to deal with objects
NS uses C++ for per-packet action
e.g. scheduler, TCP implementation
oTcl for control
Topology
Network objects
"Tool Control Language," a flexible interpreter designed primarily by John Ousterhout at UC Berkeley. Extensible and powerful, it is a viable competitor of the perl language. Tk is the X11 toolkit extension to Tcl.

6. User interface-Interactive Mode
./ns
#> set ns [new Simulator]
_o4
#> $ns at 1 "puts \"Hello World!\"" 1
#> $ns at 1.5 "exit" 2
#> $ns run
Hello World!

7. User interface-Batch Mode
simple.tcl
set ns [new Simulator]
$ns at 1 "puts \"Hello World!\""
$ns at 1.5 "exit"
$ns run
ns simple.tcl
Hello World!

8. Basic Tcl proc test{ } { set a 43 set b 27 set c [expr $a+$b]
set d [expr [expr $a - $b] * $c]
for {set k 0} {$k<10} {incr k}
if {$k<5}
puts "k<5, pow=[expr pow($d, $k)]" }
else
puts "k>=5, mod=[expr $d % $k]"
test

9. Basic oTcl Class vehicle vehicle instproc characterize{} {
$self instvar NumberOfWheels_
puts "$NumberOfWheels_ -wheel vehicle is a vehicle“ }
Class car -superclass vehicle
car instproc characterize{}
$self instvar NumberOfWheels_
puts "$NumberOfWheels_ -wheel vehicle is a car"
set a [new vehicle]
set b [new car]
$a set NumberOfWheels_ 3
$b set NumberOfWheels_ 4
$a characterize
$b characterize

10. Tcl/oTcl Common Problem
Generally useless debugging information:
no object
(_o24 cmd line 1)
invoked from within
“_o24 cmd drop-target { }”
“catch “$self cmd $args” ret”
(procedure “_o24” line 2)
Fortunately, you do NOT need to be a Tcl expert for using NS

11. Structure of a typical ns script
Creating event scheduler
Opening trace files
Creating topology
Creating the transport layer “connection”
Creating application to generate traffic
Start and stop the traffic flows

12. Structure of a typical ns script
Creating event scheduler
Opening trace files
Creating topology
Creating the transport layer “connection”
Creating application to generate traffic
Start and stop the traffic flows

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

14. Structure of a typical ns script
Creating event scheduler
Opening trace files
Creating topology
Creating the transport layer “connection”
Creating application to generate traffic
Start and stop the traffic flows

15. Open trace files Ex.1 Trace packets on all links
set fp [open test.out w]
$ns trace-all $fp
trace format:
<event> <time> <from> <to> <pkt_type> <size> <flag><flow_id><src> <dst><seq_no> <ack_seq_no>
r tcp
tcp
tcp
d tcp

16. Open trace files Ex.2 #Open the Trace file set tf [open out.tr w]
$ns trace-all $tf

17. Create Topology Create nodes Create links and queues set n0 [$ns node]
$ns <link-type> $n0de1 $node2 <bandwidth> <delay> <queue-type>
<queue-type>: DropTail, RED, WFQ, SFQ, …
<link-type>: duplex-link, simplex-link
$ns duplex-link $n0 $n1 1Mb 10ms DropTail

18. Create Flow: UDP UDP Create agents - set udp [new Agent/UDP]
- set null [new Agent/NULL]
Attach to the nodes
- $ns attach-agent $n0 $udp
- $ns attach-agent $n1 $null
Establish the “connection”
- $ns connect $udp $null

19. Create Connection: TCP
Create agents
- set tcp [new Agent/TCP]
- set tcpsink [new Agent/TCPSink]
Attach to the nodes
- $ns attach-agent $n0 $tcp
- $ns attach-agent $n1 $tcpsink
Establish the “connection”
- $ns connect $tcp $tcpsink

20. Create Application On Top of UDP: CBR On Top of TCP: FTP
set cbr0 [new Application/Traffic/CBR]
$cbr0 attach-agent $udp
On Top of TCP: FTP
set ftp [new Application/FTP]
$ftp attach-agent $tcp

21. Start & Stop the traffic
Schedule to start the traffic
$ns at 0.0 “$cbr0 start”
Schedule to stop the traffic
$ns at 5.0 “$cbr0 stop”
$ns at 5.0 “finish”
proc finish { } {
global ns fp
$ns flush-trace; close $fp
exec …. & }

22. Summary: Generic Script Structure
set ns [new Simulator]
# [Turn on tracing]
# Create topology
# Setup packet loss, link dynamics
# Create routing agents
# Create:
# - multicast groups
# - protocol agents
# - application and/or setup traffic sources
# Post-processing procs
# Start simulation

23. Example 1 - TCP Simple scenario with TCP and UDP connections n0 TCP n5
recvr
5Mb
2ms n1 n2
1.5Mb
10ms
5Mb 2ms n4
UDP n3
TCPSink

24. TCP : Step 1 Scheduler & tracing #Create scheduler
Set ns [new Simulator]
#Turn on tracing
set f [open out.tr w]
$ns trace-all $f
Set nf [open out.nam w]
$ns namtrace-all $nf

25. TCP : Step 2 Create topology #create nodes set n0 [$ns node]

26. TCP : Step 3 #create links $ns duplex-link $n0 $n1 5Mb 2ms DropTail
$ns queue-limit $n1 $n2 25
$ns queue-limit $n2 $n1 25

27. TCP : Step 4 Create TCP agents set tcp [new Agent/TCP]
set sink [new Agent/TCPSink]
$ns attach-agent $n0 $tcp
$ns attach-agent $n3 $sink
$ns connect $tcp $sink

28. TCP : Step 5 #start application traffic $ns at 1.1 “$ftp start”
Attach traffic
set ftp [new Application/FTP]
$ftp attach-agent $tcp
#start application traffic
$ns at 1.1 “$ftp start”

29. TCP : Step 6 End of simulation wrapper (as usual) $ns at 2.0 “finish”
Proc finish {} {
global ns f nf
close $f
close $nf
puts “Running nam…”
exec nam out.nam &
exit 0 }
$ns run

30. Example 2

31. Example 2 #Create a simulator object set ns [new Simulator]
#Define different colors for data flows (for NAM)
$ns color 1 Blue
$ns color 2 Red
#Open the NAM trace file
set nf [open out.nam w]
$ns namtrace-all $nf

32. Example 2 #Define a 'finish' procedure proc finish {} { global ns nf
$ns flush-trace
#Close the NAM trace file
close $nf
#Execute NAM on the trace file
exec nam out.nam &
exit 0 }

33. Example 2 #Create four nodes set n0 [$ns node] set n1 [$ns node]
#Create links between the nodes
$ns duplex-link $n0 $n2 2Mb 10ms DropTail
$ns duplex-link $n1 $n2 2Mb 10ms DropTail
$ns duplex-link $n2 $n3 1.7Mb 20ms DropTail
#Set Queue Size of link (n2-n3) to 10
$ns queue-limit $n2 $n3 10

34. Example 2 #Give node position (for NAM)
$ns duplex-link-op $n0 $n2 orient right-down
$ns duplex-link-op $n1 $n2 orient right-up
$ns duplex-link-op $n2 $n3 orient right
#Monitor the queue for link (n2-n3). (for NAM)
$ns duplex-link-op $n2 $n3 queuePos 0.5
#Setup a TCP connection
set tcp [new Agent/TCP]
$tcp set class_ 2
$ns attach-agent $n0 $tcp
set sink [new Agent/TCPSink]
$ns attach-agent $n3 $sink
$ns connect $tcp $sink
$tcp set fid_ 1

35. Example 2 #Setup a FTP over TCP connection
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ftp set type_ FTP
#Setup a UDP connection
set udp [new Agent/UDP]
$ns attach-agent $n1 $udp
set null [new Agent/Null]
$ns attach-agent $n3 $null
$ns connect $udp $null
$udp set fid_ 2

36. Example 2 #Setup a CBR over UDP connection
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set type_ CBR
$cbr set packet_size_ 1000
$cbr set rate_ 1mb
$cbr set random_ false
#Schedule events for the CBR and FTP agents
$ns at 0.1 "$cbr start"
$ns at 1.0 "$ftp start"
$ns at 4.0 "$ftp stop"
$ns at 4.5 "$cbr stop"

37. Example 2 #Detach tcp and sink agents (not really necessary)
$ns at 4.5 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"
#Call the finish procedure after 5 seconds of simulation time
$ns at 5.0 "finish"
#Print CBR packet size and interval
puts "CBR packet size = [$cbr set packet_size_]"
puts "CBR interval = [$cbr set interval_]"
#Run the simulation
$ns run

38. Tracing
cat out.tr | grep " 2 3 cbr " | grep ^r | column 1 10 | awk '{dif = $2 - old2; if(dif==0) dif = 1; if(dif > 0) {printf("%d\t%f\n", $2, ($1 - old1) / dif); old1 = $1; old2 = $2}}' > jitter.txt
Give a .tr file the user must be able to extract the useful information. A Simple unix shell script using text filters like grep and awk can extract and write to a file the required information. This can later used by Xgraph orGNUPlot etc.
This shell command selects the "CBR packet receive" event at n3, selects time (column 1)
and sequence number (column 10), and calculates the difference from last packet receive
time divided by difference in sequence number (for loss packets) for each sequence
number. The following is the corresponding jitter graph that is generated using gnuplot. The
X axis show the packet sequence number and the Y axis shows simulation time in seconds.

39. Viz Tools Nam-1 (Network AniMator Version 1) Packet-level animation
Well-supported by ns
Xgraph
Convert trace output into xgraph format

40. NAM
NAM has a nice graphical user interface similar to that of a CD player (play, fast forward, rewind, pause
and so on), and also has a display speed controller.It can graphically present information such as throughput and number of packet drops at each link, although the graphical information cannot be used for accurate simulation analysis.
For wireless simuations, however, only node movements can currently be seen in nam . Dumping of traffic data and thus visualization of data pkt movements in nam for wireless scenarios is still not supported (future
work).

41. Ns-nam Interface Color Node manipulation Link manipulation
Topology layout
Protocol state
Misc

42. Nam Interface: Color Color mapping Color  flow id association
$ns color 40 red
$ns color 41 blue
$ns color 42 chocolate
Color  flow id association
$tcp0 set fid_ 40 ;# red packets
$tcp1 set fid_ 41 ;# blue packets

43. Nam Interface: Nodes Color Shape (can’t be changed after sim starts)
$node color red
Shape (can’t be changed after sim starts)
$node shape box ;# circle, box, hexagon
Marks (concentric “shapes”)
$ns at 1.0 “$n0 add-mark m0 blue box”
$ns at 2.0 “$n0 delete-mark m0”
Label (single string)
$ns at 1.1 “$n0 label \”web cache 0\””

44. Nam Interface: Links Color Label Dynamics (automatically handled)
$ns duplex-link-op $n0 $n1 color "green"
Label
$ns duplex-link-op $n0 $n1 label "abced"
Dynamics (automatically handled)
$ns rtmodel Deterministic { } $n0 $n1
Asymmetric links not allowed

45. Nam Interface: Topo Layout
“Manual” layout: specify everything
$ns duplex-link-op $n(0) $n(1) orient right
$ns duplex-link-op $n(1) $n(2) orient right-up
$ns duplex-link-op $n(2) $n(3) orient down
$ns duplex-link-op $n(3) $n(4) orient 60deg
If anything missing  automatic layout

46. Nam Interface: Protocol State
Monitor values of agent variables
$ns add-agent-trace $srm0 srm_agent0
$ns monitor-agent-trace $srm0
$srm0 tracevar C1_
$srm0 tracevar C2_
# … …
$ns delete-agent-trace $tcp1

47. Nam Interface: Misc Annotation Set animation rate
Add textual explanation to your sim
$ns at 3.5 "$ns trace-annotate \“packet drop\"“
Set animation rate
$ns at 0.0 "$ns set-animation-rate 0.1ms"

48. Useful Pointers Directory structure:
/ns-2.../ contains C++ code
/ns-2.../tcl/lib/ contains oTcl source code
/ns-2.../tcl/ex/ examples simulation scripts
/ns-2.../tcl/test/ validation test scripts
RED Queue Monitor Example

49. Xgraph

50. Other Utilities in Ns Nam editor Tcl debugger Topology generator
Available as part of nam-1
Tcl debugger
For source and documentation, see
Topology generator
Scenario generator

51. Resources Ns distribution download Installation problems and bug-fix
Installation problems and bug-fix
Ns-users mailing list
See
Archives from above URL

52. Resources (contd..) Marc Greis’ tutorial Ns-users archive Ns-manual
Ns-users archive
Ns-manual
Tcl (Tool Command Language)
Practical programming in Tcl and Tk, Brent Welch
Otcl (MIT Object Tcl)
~otcl/doc/tutorial.html (in distribution)

53. Resources (contd..)
NS Frequently Asked Questions:
Lloyd Wood - introducing ns:

54. QUESTIONS
???