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
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 (http://nile.wpi.edu/NS/)
 Where is documentation and Tutorials:
 http://www.isi.edu/nsnam/ns/ns-documentation.html
 http://www.isi.edu/nsnam/ns/tutorial/
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
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
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
User interface-Interactive
Mode
adeel@laptop#> ./ns
#> set ns [new Simulator]
_o4
#> $ns at 1 "puts \"Hello World!\""
1
#> $ns at 1.5 "exit"
2
#> $ns run
Hello World!
User interface-Batch Mode
simple.tcl
set ns [new Simulator]
$ns at 1 "puts \"Hello World!\""
$ns at 1.5 "exit"
$ns run
adeel@laptop#> ns simple.tcl
Hello World!
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
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
$b characterize
Tcl/oTcl Common Problem
 Generally useless debugging information:
no object
(_o24 cmd line 1)
invoked from within
“_o24 cmd drop-target { }”
invoked from within
“catch “$self cmd $args” ret”
(procedure “_o24” line 2)
 Fortunately, you do NOT need to be a Tcl expert
for using NS
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
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
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
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
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 1 0 2 tcp 1000 - - - - - - - - - - - - - - - - - 0
+ 1 0 2 tcp 1000 - - - - - - - - - - - - - - - - - 0
0.0 3.1 29
0.0 3.1 29
199
199
- 1 0 2 tcp 1000 - - - - - - - - - - - - - - - - - 0 0.0 3.1 29
199
199
d 1.00234 0 2 tcp 1000 - - - - - - - - - - - - 0
0.0 3.1 29
Open trace files Ex.2
#Open the Trace file

set tf [open out.tr w]

$ns trace-all $tf
Create Topology
 Create nodes
 set n0 [$ns node]
 set n1 [$ns node]
 Create links and queues
 $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
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
Create Connection: TCP
 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
Create Application
 On Top of UDP: CBR
 set cbr0 [new Application/Traffic/CBR]
 $cbr0 attach-agent $udp
 On Top of TCP: FTP
 set ftp [new Application/FTP]
 $ftp attach-agent $tcp
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 …. &
}
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
Example 1 - TCP
 Simple scenario with TCP and UDP
connections
n0
TCP
5Mb
2ms
n2
n1
1.5Mb
10ms
n4
UDP
n5
UDP
recvr
5Mb
2ms
n3
TCPSink
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 $nf
TCP : Step 2
 Create topology
#create nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
TCP : Step 3
#create links
$ns duplex-link $n0 $n1 5Mb 2ms DropTail
$ns duplex-link $n1 $n2 1.5Mb 10ms DropTail
$ns duplex-link $n2 $n3 5Mb 2ms DropTail
$ns queue-limit $n1 $n2 25
$ns queue-limit $n2 $n1 25
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
TCP : Step 5
 Attach traffic
set ftp [new Application/FTP]
$ftp attach-agent $tcp
#start application traffic
$ns at 1.1 “$ftp start”
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
Example 2
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
Example 2
#Define a 'finish' procedure

proc finish {} {

global ns nf

$ns flush-trace

#Close the NAM trace file

close $nf

#Execute NAM on the trace file

exec nam out.nam &

exit 0

}
Example 2
#Create four nodes
 set n0 [$ns node]
 set n1 [$ns node]
 set n2 [$ns node]
 set n3 [$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
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
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
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"
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
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
Viz Tools
Nam-1 (Network AniMator Version 1)
 Packet-level animation
 Well-supported by ns
Xgraph
 Convert trace output into xgraph format
NAM
Ns-nam Interface
 Color
 Node manipulation
 Link manipulation
 Topology layout
 Protocol state
 Misc
Nam Interface: Color
 Color mapping
$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
Nam Interface: Nodes
 Color
$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\””
Nam Interface: Links
 Color
$ns duplex-link-op $n0 $n1 color "green"
 Label
$ns duplex-link-op $n0 $n1 label "abced"
 Dynamics (automatically handled)
$ns rtmodel Deterministic {2.0 0.9 0.1} $n0 $n1
 Asymmetric links not allowed
Nam Interface: Topo Layout
 “Manual” layout: specify everything
$ns
$ns
$ns
$ns
duplex-link-op
duplex-link-op
duplex-link-op
duplex-link-op
$n(0)
$n(1)
$n(2)
$n(3)
$n(1)
$n(2)
$n(3)
$n(4)
orient
orient
orient
orient
right
right-up
down
60deg
 If anything missing  automatic
layout
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
Nam Interface: Misc
 Annotation
 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"
Useful Pointers
 Directory structure:
/ns-2.../
contains C++ code
/ns-2.../tcl/lib/
contains oTcl source code
examples simulation scripts
validation test scripts
/ns-2.../tcl/ex/
/ns-2.../tcl/test/
 RED Queue Monitor Example
 http://nile.wpi.edu/NS
Xgraph
Other Utilities in Ns
 Nam editor
Available as part of nam-1
 Tcl debugger
For source and documentation, see
http://www.isi.edu/nsnam/ns/ns-debugging.html
 Topology generator
http://www.isi.edu/nsnam/ns/ns-topogen.html
 Scenario generator
http://www.isi.edu/nsnam/ns/ns-scengeneration.html
Resources
 Ns distribution download
 http://www.isi.edu/nsnam/ns/ns-build.html
 Installation problems and bug-fix
 http://www.isi.edu/nsnam/ns/ns-problems.html
 Ns-users mailing list
 Ns-users@isi.edu
 See http://www.isi.edu/nsnam/ns/ns-lists.html
 Archives from above URL
Resources (contd..)
 Marc Greis’ tutorial
 http://www.isi.edu/nsnam/ns/tutorial
 Ns-users archive
 Ns-manual
 http://www.isi.edu/nsnam/ns/ns-documentation.html
 Tcl (Tool Command Language)
 http://dev.scriptics.com/scripting
 Practical programming in Tcl and Tk, Brent Welch
 Otcl (MIT Object Tcl)
 ~otcl/doc/tutorial.html (in distribution)
Resources (contd..)
 NS Frequently Asked Questions:
http://www.isi.edu/nsnam/ns/ns-faq.html
 Lloyd Wood - introducing ns:
http://www.ee.surrey.ac.uk/Personal/L.Wood/ns/
QUESTIONS
 ???