1. Introduction to Mobility & Network Simulator 2 (NS-2)
Mahmood Hasanlou
Department of Computer Engineering
Sharif University of Technology

2. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

3. Random Walk Mobility Model
Since many entities in nature move in extremely unpredictable ways, the Random Walk Mobility Model was developed to mimic this erratic movement
In this mobility model, an MN moves from its current location to a new location by randomly choosing a direction and speed in which to travel
The new speed and direction are both chosen from pre-defined ranges, [speedmin; speedmax] and [0;2p] respectively
Sharif university of Technology

4. Random Walk Mobility Model
Each movement in the Random Walk Mobility Model occurs in either a constant time interval t or a constant distance traveled d, at the end of which a new direction and speed are calculated
If an MN which moves according to this model reaches a simulation boundary, it “bounces” off the simulation border with an angle determined by the incoming direction
The MN then continues along this new path
Sharif university of Technology

5. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

6. Random Waypoint Mobility Model (RWPM)
The Random Waypoint Mobility Model includes pause times between changes in direction and/or speed
An MN begins by staying in one location for a certain period of time (i.e., a pause time)
Once this time expires, the MN chooses a random destination in the simulation area and a speed that is uniformly distributed between [minspeed, maxspeed]
Sharif university of Technology

7. Random Waypoint Mobility Model (RWPM)
The MN then travels toward the newly chosen destination at the selected speed
Upon arrival, the MN pauses for a specified time period before starting the process again
We note that the movement pattern of an MN using the Random Waypoint Mobility Model is similar to the Random Walk Mobility Model if pause time is zero and [minspeed, maxspeed] = [speedmin, speedmax]
Sharif university of Technology

8. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

9. Network Simulator (NS)
ns is an object oriented simulator, written in C++, with an OTcl interpreter as a frontend
The simulator supports a class hierarchy in C++ (also called the compiled hierarchy in this document), and a similar class hierarchy within the OTcl interpreter (also called the interpreted hierarchy in this document)
The two hierarchies are closely related to each other; from the user’s perspective, there is a one-to-one correspondence between a class in the interpreted hierarchy and one in the compiled hierarchy
The root of this hierarchy is the class TclObject
Sharif university of Technology

10. Network Simulator (NS)
Users create new simulator objects through the interpreter; these objects are instantiated within the interpreter, and are closely mirrored by a corresponding object in the compiled hierarchy
The interpreted class hierarchy is automatically established through methods defined in the class TclClass
user instantiated objects are mirrored through methods defined in the class TclObject
Sharif university of Technology

11. Sharif university of Technology
Why two languages?
ns uses two languages because simulator has two different kinds of things it needs to do
On one hand, detailed simulations of protocols requires a systems programming language which can efficiently manipulate bytes, packet headers, and implement algorithms that run over large data sets
For these tasks run-time speed is important and turn-aroundtime (run simulation, find bug, fix bug, recompile, re-run) is less important
Sharif university of Technology

12. Sharif university of Technology
Why two languages?
On the other hand, a large part of network research involves slightly varying parameters or configurations, or quickly exploring a number of scenarios
In these cases, iteration time (change the model and re-run) is more important
Since configuration runs once (at the beginning of the simulation), run-time of this part of the task is less important
Sharif university of Technology

13. Sharif university of Technology
Why two languages?
ns meets both of these needs with two languages, C++ and OTcl
C++ is fast to run but slower to change, making it suitable for detailed protocol implementation
OTcl runs much slower but can be changed very quickly (and interactively), making it ideal for simulation configuration
Sharif university of Technology

14. Which language for what?
Having two languages raises the question of which language should be used for what purpose
Our basic advice is to use OTcl:
for configuration, setup, and “one-time” stuff
if you can do what you want by manipulating existing C++ objects
and use C++:
if you are doing anything that requires processing each packet of a flow
if you have to change the behavior of an existing C++ class in ways that weren’t anticipated
Sharif university of Technology

15. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

16. Mobile Networking in ns
The functions and procedures described in this subsection can be found in ~ns/mobilenode.{cc,h}, ~ns/tcl/lib/ns-mobilenode.tcl, ~ns/tcl/mobility/dsdv.tcl, ~ns/tcl/mobility/dsr.tcl, ~ns/tcl/mobility/tora.tcl
Example scripts can be found in ~ns/tcl/ex/wireless-test.tcl and ~ns/tcl/ex/wireless.tcl
Sharif university of Technology

17. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

18. Sharif university of Technology
Simulation Scenario
We start by presenting simple script that run single TCP connection over 3-nodes over an area of size 500m over 400m
The location process is as follow :
The initial locations of nodes 0, 1 and 2 are respectively (5,5), (490,285) and (150,240)
At time 10, node 0 starts moving towards point (250,250) at a speed of 3m/s
At time 15, node 1 starts moving towards point (45,285) at a speed of 5m/s
At time 20, node 0 starts moving towards point (480,300) at a speed of 5m/s
Node 2 is still throughout the simulation
The simulation lasts 150s. At time 10 a TCP connection is initiated between node 0 and node 1
Sharif university of Technology

19. Sharif university of Technology
Writing the TCL script
We begin by specifying some basic parameters for the simulation :
set val(chan) Channel/WirelessChannel set val(prop) Propagation/TwoRayGround set val(netif) Phy/WirelessPhy set val(mac) Mac/802_11 set val(ifq) Queue/DropTail/PriQueue set val(ll) LL set val(ant) Antenna/OmniAntenna set val(ifqlen) 50 ;# max packet in ifq set val(x) 800;# X dimension of the topography set val(y) 800;# Y dimension of the topography set val(nn) 30 ;# number of nodes set val(rp) DSDV set val(stop) 150 ;# simulation time
These parameters are used in configuring of the nodes
Sharif university of Technology

20. Configures of a mobile 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 ON
For {set $i 0} {$i < $val(nn)} {incr $i} {
set node_($i) [$ns node] }
Sharif university of Technology

21. Initial location and movement of nodes
The initial location of node 0 given as follows :
$node_(0) set X_ 5.0
$node_(0) set Y_ 5.0
$node_(0) set Z_ 5.0
A linear movement of a node is generated by specifying the time in which it start, the x and y values of the target point and the speed:
$ns at 15.0 “$node_(1) setdest ”
Sharif university of Technology

22. Sharif university of Technology
Ending the simulation
We need to create the initial node position for nam using
For {set $i 0} {$i < $val(nn)} {incr $i} {
$ns initial_node_pos $node_($i) 30 }
We tell nodes when the simulation ends with :
$ns at $val(stop) “node_($i) reset”
Sharif university of Technology

23. Sharif university of Technology
Outline
Random Walk Mobility Model
Random Waypoint Mobility Model
Network Simulator
Mobile Networking in ns
Simulation Scenario
Home Work 2
Sharif university of Technology

24. Sharif university of Technology
Home Work 2
You must look at the mobile node source code and determine which of the mobility models support in it ?
You simulate a scenario and obtain it’s result with mobility model that exist
Then you must change that mobility model to another
You simulate your scenario again with this new mobility model and compare the result of this by previous results
Scenario is the same scenario of the HW1
Sharif university of Technology

25. Sharif university of Technology
Refrence
A collaboration between researchers at UC Berkeley, LBL, USC/ISI, and Xerox PARC, “The NS Manual”, 2005
Lecture Notes Univ. de Los andes, Merida, Venezuela, and ESSI, “NS simulator for beginners”
Tracy Camp, Jeff Boleng, Vanessa Davies, “A Survey of Mobility Models for Ad Hoc Network Research” , 2002
Sharif university of Technology