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…

Arrays of C Program

Arrays in C programming starts with memory addresses. Yes the compiler handles arrays as memory addresses.
  • Similar elements group together with a single name is called array
  • the indexing always starts with 0 and ends at n-1 (if the size of the array is n)
  • Array elements stores in consecutive memory location.
The array elements usually stores in consecutive memory location. For example,
int a[10];  //Array with size 10
the above example is an integer array with size 10 or this array can hold 10 variables.
The elements starts from a[0], a[1], a[2]…..a[9], so totally there are 10 elements.
Array elements values memory address location
a[0] 32 600AH  (This address is called as the base address)
a[1] 34 600EH
a[2] 23 6012H
a[3] 35 6016H
a[4] 45 601AH
a[5] 67 601EH
a[6] 56 6022H
a[7] 1 6026H
a[8] 34 602AH
a[9] 25 602EH
The memory addresses shown above are in hexadecimal, that’s why each address suffixed with a letter H. The memory addresses in each machine will be different.
The base address is the address where the first element of the array is stored. Usually it is represented as &a[0] or simply a.
The entire array is represented as an address by specifying the base address alone to various other elements of C programming like passing array to functions involves sending the base address only.
For the above table, here is the declaration syntax
int a[10]={32,34,23,35,45,67,56,1,34,25};
or
int a[]={32,34,23,35,45,67,56,1,34,25};
A simple program to get some numbers and print them on the screen
int main()
{
int a[10], j; //declaration of array “a” and its index j
printf(“Enter all the 10 numbers”);
for(j=0;j<10;j++) //get the numbers using a for loop which executes for 10 times (0 to 9)
{
scanf(“%d”, &a[j]);
}
for(j=0;j<10;j++) //print the numbers using a for loop which executes for 10 times (0 to 9)
{
printf(“%d”,a[j]);
}
return 0;
}
In the above example, j varies from 0 to 9 which means the loop will execute 10 times for the array a like this
a[j] when j=0 then a[0]
a[j] when j=1 then a[1]
a[j] when j=2 then a[2]…. and so on
like this the input is entered through the keyboard and same for printing the output.

 T S Pradeep Kumar

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