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…

User Defined Functions in C

Almost all the programming languages uses functions. Functions are the entities which are grouping a set of statements which do a specific job or set of jobs.
Example: sum of integers, sum of float number, complex number addition.
All the above three can be implemented as a single function or three separate functions.
When someone wants to use that, a function can be simply called.
So function implementation happens as
  • Function prototype or Function declaration
  • Function definition or function implementation
  • Function call
Function prototype
  • It is necessary to specify the name of the function, the parameters and the return type to the compiler that the function is being defined in this program.
  • The prototype ends with a semicolon
syntax:
int sum(int, int); //function prototype
Function Definition
This is the actual function definition which shows the function implementation.
for the above syntax here is the function
int sum(int a, int b)
{
int c;
c=a+b;
return c;
}
The above function is returning an integer, hence int is specified. If a function is not returning any thing, a void can be used.
Function call
The last is the function call, which when being needed a simple call will make the function to work. Here is the example
int main()
{
int x,y,z;
scanf(“%d %d”,&x,&y);
z=sum(x,y); //function call
printf(“The sum is %d”, z);
return 0;
}
Once the function is called, the control goes to the actual implementation and execute the statements inside the function and the value is returned to the main function.
Components of a function
  1. Name of the function
  2. Return type
  3. Parameters or arguments
In the above example
name of the function is : sum()
return type is : int
parameters are: int, int

 T S Pradeep Kumar

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