Queuing Models in NS2

Image
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…

Decision Making and Looping

C supports Decision Making and Looping (Interations)
In decision Making,
if, if-else, if- else if – else, switch – case is used.
if(condition)
{
//These statements are executed only if the condition is true or 1
}
if – else
if(condition)
{
//These statements are executed only if the condition is true or 1
}
else
{
//these statement are executed only if the condition is false or 0
}
(in the above example, there is no else part means that for some situation, there may not be a need for else part)
if – else if – else
if(condition 1)
{
//These statements are executed if the condition 1 is true or 1
}
else if (condition 2)
{
//These statements are executed if the condition 2 is true or 1
}
else
{
//These statements are executed neither condition 1 nor condition 2 are true
// if all the conditions fails, then this statement will execute
}
Switch Case
switch (expression)
{
case 1: statement 1;
break;
case 2: statement 2;
break;
case 3: statement 3;
break;
default: statement d;
break;
}
//Statement n;
The switch case works similar like a multiple if else if statement.
Assume if the expression takes 3 as the value and the statement 3 will be executed and next there is a break statement, so the control comes to statement n and it ill be printed.
so when case 3: is success, then
statement 3;
statement n;
will be printed
Looping
  • while()
  • do .. while();
  • for()
while ()
while(condition)
{
//statement 1
}
statement 1 will keep on execution till the condition becomes false
so this loop is called as entry controlled loop
do while()
do
{
//Statement 1
}while(condition);
in this, whether the condition is true or false, first time the loop will execute and only then it will check for validity of the condition.
so this loop is called as exit controlled loop
for loop
for (initialization: condition; increment/decrement)
{
//Statement
}
More details about the looping will be in subsequent posts.

 T S Pradeep Kumar

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