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…

Linux for NS2 (Network Simulator 2)

At many places, I happen to see researchers and students wanted to use Windows for NS2 rather than Linux. The reason may be,
  • Linux is tough
  • It occupies more space and more memory in my Computer
  • Linux uses lot of commands and i am not aware of it
  • Tough to handle dual boot OS (windows and Linux)
  • always wanted to be in the cakewalk. (never try a new thing)
  • etc
But here are some basic tips for using NS2 under a Linux Machine.
  • It is enough to know some basic Linux commands to work with NS2 (hardly not more than 20 commands)
  • One should have a basic knowledge of how tree structure in Linux/Unix look like
  • Finally, where to set the PATH information in Linux
With all the above three, one can confidentally work on Linux. As for as windows is concerned, upto NS2.27 version is tested under windows and recent versions there is no hope (however it will work fine, but "Use at your Own Risk")
Please see this post to install Fedora 12 in your Computer
Now we will see some basic Linux commands that are needed for NS2.
  1. ls => listing the file contents
  2. ls -l => listing the file in long format, it tells you about the ownership and permissions
  3. chmod => Changing the mode of the file (syntax is chmod 755 <filename>
  4. echo => it echo the value to the screen 
    1. Example: echo name 
    2. echo $SHELL (it will print the name of the shell)
    3. echo $USER (it will print the name of the user)
    4. echo $PATH (it display the values contained in the PATH variable)
    5. echo $HOME (it displays the home folder of the user) (Now you can understood that the variable names are denoted using a $ symbol)
  5. pwd => it is just present working directory
  6. make => (it executes the instructions given in the Makefile which is available under that directory)
  7. gcc filename.cxx => A command to run the gcc compiler (This is not necessarily needed for NS2, but as a developer, you should know)
  8. ./install  => (See a dot in the beginning, it is just executing the install file which is available under a folder, any executable can be executed with the help of this ./)
  9. passwd => changing the password of the current user
  10. cd => change the directory
  11. mkdir => make a directory
  12. gedit => it is similar like a notepad editor in windows(syntax is gedit filename)
  13. vi => it is vi editor
Path setting
The path can be set in a file which is available for each user of the Linux OS.  For example, a user called  "pradeep" will have the home folder as /home/pradeep and another user "kumar" has home folder as /home/kumar
Each user "pradeep" and "kumar" will have a file called .bash_profile (in case of redhat and fedora) and .bashrc (Ubuntu, etc) in their home folder. This file is a hidden file which can be opened using a vi or gedit editor
The command being
vi /home/pradeep/.bash_profile
vi /home/pradeep/.bashrc

or
gedit /home/pradeep/.bash_profile
gedit /home/pradeep/.bashrc
Similarly the same for user "kumar" (if you set the path for "pradeep" and running under "kumar", it will not work, for that to work, there is a separate customisation is available), for beginners, these steps are enough.


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