Queuing Models in NS2

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M/M/1 is a system with poisson arrival time, servicing exponentially and a queue of unlimited capacity and type of FIFO Queue. This is the simplest queuing system.  NS2 supports various distributions like pareto, exponential, constant, unifrom, etc to handle the network dynamics and metrics. So it is very easy to test the given network link to monitor a given queue using any of these queuing models. The listing 3 and 4 are monitoring the link when DropTail queue is used with a capacity of finite and infinite. Listing 13.3 uses infinite capacity and Listing 13.4 uses Finite capacity The output screen shot is shown below the scripts for further understanding
Listing 3 – M/M/1 Queuing Model #new Simulator creation set ns [new Simulator] #trace file creation for capturing the UDP data set tf [open out.tr w] $ns trace-all $tf
#setting the exponential distribution param set lambda 30.0 set mu     33.0
#creation of nodes set n1 [$ns node] set n2 [$ns node] #The queue limit is 1Lakh as the capacity is infin…

Xgraph

Xgraph is an X-Windows application that includes:

  • interactive plotting and graphing
  • animation and deritives
  • portability and bug fixes

So to plot the characteristics of NS2 parameters like throughput, end to end delay, packets information, etc can be plotted using xgraph
The successful installation of NS2 will install xgraph also along with it.
To run xgraph from a shell prompt: # xgraph filename.xg

inside TCL scripts, xgraph can be written like this
exec xgraph filename.xg -geometry 500×500
if there are more xgraph files then,
exec xgraph filename1.xg -geometry 500×500 &
exec xgraph filename2.xg -geometry 500×500 &
The ambersand is mandatory to popup all the graph windows, if & (ambersand) is not there, then only the last xgraph window will be popped up.

Sample xgraph file and its contents
/*** The xgraph file shows the information about the overhead with size of the network,
Overhead is compared with four routing protocols like AODV, DSR, DSDV and NEAODV (my own algorithm)
the values are taken from various trace files.
To execute the following xgraph file, copy the following contents and save it as “example.xg” possibly (other formats also supported) and in the shell prompt # xgraph example.xg
TitleText: Overhead (Kbits/s) Vs Network Size
YUnitText: OverHead
XUnitText: Network Size (nodes)
“NEAODV”
200 100
400 350
600 800
800 1200

“AODV”
200 500
400 1600
600 2300
800 3700

“DSR”
200 100
400 320
600 400
800 600

“DSDV”
200 500
400 3700
600 6400
800 11600
Output window will be looking like this

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