The document provides instructions for creating mobile nodes and running wireless simulations in the NS-2 network simulator. It discusses: 1. Configuring mobile nodes by specifying options like MAC type, interface queue length, and topology before creating them. Common configuration parameters and their usage are also described. 2. Creating a topology object to define the simulation area and loading grid coordinates. 3. Initializing a General Operations Director (GOD) object to track mobile node locations. 4. An example simulation script that defines parameters, creates nodes, sets up TCP traffic, and produces node movements over time. 5. Types of traces produced during wireless simulations and how to identify them.

1. Running Wireless Simulations in NS
Creating a Mobile Node in NS
o A mobile node consists of a number of network components:
 Link Layer (LL) - tell node how to check packet integrity
 Interface Queue (IfQ) - buffer size
 MAC layer - tell node how to share broadcast medium
o NS supports different kinds of mobile network simulations;
You MUST configure the mobile nodes before you can create them.
o
o
Mobile nodes are configured using the command $ns node-config)
followed by one or more (name, value) pairs
The configuration API of mobile nodes looks as follows:
set ns_
[new Simulator]
# Configure mobile nodes
$ns_ node-config OPTION1 VALUE1 [OPTION2 VALUE2]...
o
Example: create mobile nodes that uses IEEE 802.11 MAC protocol
set ns_
[new Simulator]
# Configure mobile nodes
$ns_ node-config -macType
o
Mac/802_11
Example: create mobile nodes that uses IEEE 802.11 MAC protocol and
with a buffer of 50 packets
set ns_
[new Simulator]

2. # Configure mobile nodes
$ns_ node-config -macType
-ifqLen
o
Mac/802_11
50
Node configuration API may consist of:
 defining the type of addressing (flat/hierarchical etc)
 the type of adhoc routing protocol
 Link Layer
 MAC layer
 IfQ
 etc.
Configuring Mobile Nodes
o The following table contains the parameters and the most commonly
used options (802.11 network)
Option Name
Usage
How node
addressingType addresses are
organized
Routing
protocol used
by nodes in an
-adhocRouting
Ad Hoc
network (noninfrastructure)
Option values



flat
hierarchical
expanded



DSDV
DSR (Source Routing)
TORA
-llType
Link Layer
protocol

LL
-macType
MAC Layer
protocol

Mac/802_11
-propType
How radio
wave
propagate

Propagation/TwoRayGround

3. -ifqType
Queueing
method at the
interface
-ifqLen

Queue/DropTail/PriQueue
Queue size at
the interface

integer (e.g., 50)
-phyType
Type of
physical layer

Phy/WirelessPhy
-antType
Type of
antenna

Antenna/OmniAntenna
-channelType
Type of
channel

Channel/WirelessChannel

Create a topology object:
set topo [new Topography]
Define the grid size:
$topo load_flatgrid 500 500
Use the variable $topo as
parameter for this option
Description of
the wireless
-topoInstance
network
topology
-agentTrace
Flag to enable
writing of
trace data for
agent module
-routerTrace
Flag to enable
writing of
trace data for
wireless router
module
-macTrace
Flag to enable
writing of
trace data for
wireless MAC
module
Flag to enable
writing of
trace data for
-movementTrace
the movement
of wireless
nodes
o
NOTE:




ON
OFF


ON
OFF


ON
OFF


ON
OFF

4. All default values for these options are NULL except: addressingType: flat
Common values used in Wireless Simulation
o A very common way to keep option values in a single place is to used
an associative array (the indices of the array are names instead of
numbers)
o Here are some commonly used values for wireless simulations:
#
===========================================================
===========
# Define options
#
===========================================================
===========
set val(chan)
Channel/WirelessChannel ;# channel
type
set val(prop)
Propagation/TwoRayGround ;# radiopropagation model
set val(ant)
Antenna/OmniAntenna
;# Antenna
type
set val(ll)
LL
;# Link
layer type
set val(ifq)
Queue/DropTail/PriQueue ;#
Interface queue type
set val(ifqlen)
50
;# max
packet in ifq
set val(netif)
Phy/WirelessPhy
;# network
interface type
set val(mac)
Mac/802_11
;# MAC type
set val(rp)
DSDV
;# ad-hoc
routing protocol
o
After storing the values in the associative array $val, we can set the
options of wireless nodes as follows:
# ==================================================
# Configure nodes
# ==================================================
$ns_ node-config
-channelType $val(chan)
-propType $val(prop)
-antType $val(ant)
-llType $val(ll)
-ifqType $val(ifq)
-ifqLen $val(ifqlen)
-phyType $val(netif)

5. -macType $val(mac)
-adhocRouting $val(rp)
-agentTrace ON
-routerTrace ON
-macTrace OFF
-movementTrace OFF
-topoInstance $topo

Don't worry about the variable $topo, we will cover that later.
Topology
o The wireless simulation needs to know the area in which the wireless
nodes can travel...
o For this purpose, NS has defined a Topology class to store information
about the mobile hosts that move in a grid...
o The create a Topology object, use:
set VARNAME [new Topography]
EXAMPLE:
set topo [new Topography]
o
To provide the topography object with x and y co-ordinates of the
boundary, use:
$TOPO_VARNAME load_flatgrid
X-SIZE
EXAMPLE:
$topo

load_flatgrid
500
500
Default granularity is 1
The General Operations Director (GOD) Object
Y-SIZE
[Granularity]

6. o
o
o
o
o
Unlike wired (immobile) network simulation, the location of mobile
hosts are not known when the simulation is in progress.
In order to determine whether 2 mobile nodes can communicate with
each other (i.e., whether they are within each others' range), NS needs to
find out their locations.
So NS must maintain some necessary information on ALL mobile
hosts
NS has defined a class to do so, and it is called "GOD" (General
Operations Director) - the acronym "GOD" seems appropriate since
this object knows information about every mobile hosts :-)
Before you can create a mobile host, you MUST first create
a "GOD" object, using the following command:
create-god
NUMBER-Of-Mobile-Nodes
The parameter NUMBER-Of-Mobile-Nodes is the number of mobile
hosts in the wireless simulation (you need to tell NS the amount of
space to reserve)
Some more information of the GOD class object:

o
The GOD (General Operations Director) object is used to store global
information about the state of the environment, network or nodes that an
omniscent observer would have, but that should not be made known to any
participant in the simulation.
A GOD object stores the total number of mobile nodes and a table of
shortest number of hops required to reach from one node to another.
The next hop information is loaded into GOD object from movement
pattern files, before simulation begins, since calculating this on the fly
during simulation runs can be quite time consuming.
o
NOTE:
Only ONE single global instance of the GOD object is to be
created during an NS simulation !!!
How to write a Wireless Simulation in NS
o OK, we know enough to write a simple wireless simulation in NS

7. o
o
Simulated Scenario:
Simulation program:
# simple-wireless.tcl
# A simple example for wireless simulation
#
===========================================================
===========
# Define options
#
===========================================================
===========
set val(chan)
Channel/WirelessChannel
;#
channel type
set val(prop)
Propagation/TwoRayGround
;#
radio-propagation model
set val(netif)
Phy/WirelessPhy
;#
network interface type
set val(mac)
Mac/802_11
;# MAC
type
set val(ifq)
Queue/DropTail/PriQueue
;#
interface queue type
set val(ll)
LL
;# link
layer type
set val(ant)
Antenna/OmniAntenna
;#
antenna model
set val(ifqlen)
50
;# max
packet in ifq
set val(nn)
2
;#
number of mobilenodes
set val(rp)
DSDV
;#
routing protocol
#
===========================================================
===========
# Main Program
#
===========================================================
===========
#
# Initialize Global Variables
#
set ns_
[new Simulator]
set tracefd
[open simple.tr w]
$ns_ trace-all $tracefd
# ---------------------------------------------------------------# Set up wireless network simulation

8. # ---------------------------------------------------------------# Create topography object to hold wireless scenario
set topo
[new Topography]
$topo load_flatgrid 500 500
500x500
;# Grid size is
#
# Create god object
#
create-god $val(nn)
#
# Create the specified number of mobilenodes [$val(nn)]
and "attach" them
# to the channel.
# Here two nodes are created : node(0) and node(1)
# configure node
$ns_ node-config -adhocRouting $val(rp)
-llType $val(ll)
-macType $val(mac)
-ifqType $val(ifq)
-ifqLen $val(ifqlen)
-antType $val(ant)
-propType $val(prop)
-phyType $val(netif)
-channelType $val(chan)
-topoInstance $topo
-agentTrace ON
-routerTrace ON
-macTrace OFF
-movementTrace OFF
# -------------------------------------------------------# Direct mobile node's movements
# -------------------------------------------------------for {set i 0} {$i< $val(nn) } {incri} {
set node_($i) [$ns_ node]
$node_($i) random-motion 0
random motion
}
;# disable
#
# Provide initial (X,Y, for now Z=0) co-ordinates for
mobilenodes
#
$node_(0) set X_ 5.0
$node_(0) set Y_ 2.0
$node_(0) set Z_ 0.0

9. $node_(1) set X_ 390.0
$node_(1) set Y_ 385.0
$node_(1) set Z_ 0.0
#
# Now produce some simple node movements
# Node_(1) starts to move towards node_(0)
#
$ns_ at 50.0 "$node_(1) setdest 25.0 20.0 15.0"
$ns_ at 10.0 "$node_(0) setdest 20.0 18.0 1.0"
# Node_(1) then starts to move away from node_(0)
$ns_ at 100.0 "$node_(1) setdest 490.0 480.0 15.0"
# -------------------------------------------------------------# The rest is "ordinary" network connection setup
# -------------------------------------------------------------# Setup TCP connections between node_(0) and node_(1)
set tcp [new Agent/TCP]
$ns_ attach-agent $node_(0) $tcp
$tcp set class_ 2
set sink [new Agent/TCPSink]
$ns_ attach-agent $node_(1) $sink
$ns_ connect $tcp $sink
# Setup FTP flow for TCP connection
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ns_ at 10.0 "$ftp start"
#
# Tell nodes when the simulation ends
#
for {set i 0} {$i< $val(nn) } {incri} {
$ns_ at 150.0 "$node_($i) reset";
}
$ns_ at 150.0 "stop"
$ns_ at 150.01 "puts "NS EXITING..." ; $ns_ halt"
proc stop {} {
global ns_ tracefd
$ns_ flush-trace
close $tracefd
}
puts "Starting Simulation..."

10. $ns_ run
o
Example Program: (Demo above code)
 Prog file: click here
Trace Information from Wireless Simulation
o AgentTraces are marked with AGT in the 5th field
o RouterTrace are marked with RTR in the 5th field
o MacTrace are marked with MAC in the 5th fields.
o MovementTrace (shows the movement of the mobile nodes) are marked
with M in the 2nd field.
References
o Marc Greis' NS Tutorial Chapter IX. Running Wireless Simulations in ns
- click here