The document contains instructions for implementing three network algorithms in C/C++: 1) An error detecting code using CRC CCIT(16 bits), 2) A distance vector algorithm to find suitable transmission paths, and 3) A congestion control algorithm using the leaky bucket method. Sample code is provided for each algorithm to calculate checksums, routing tables, and regulate output rate based on bucket size.

1. Networks Laboratory – 10CSL77 PART - B
Implement the following in C/C++:
1. Write a program for error detecting code using CRC CCIT(16 bits).
#include<stdio.h>
#include<string.h>
#define N strlen(g)
char t[128],cs[128],g[]="10001000000100001";
int a,e,c;
void xor()
{
for(c=1;c<N;c++)
cs[c]=((cs[c] == g[c])?'0':'1');
}
void crc()
{
for(e=0;e<N;e++)
cs[e]=t[e];
do{
if(cs[0]=='1')
xor( );
for(c=0;c<N-1;c++)
cs[c]=cs[c+1];
cs[c]=t[e++];
}while(e<=a+N-1);
}
int main()
{
int flag=0;
system("clear");
printf("Enter polynomial:n");
scanf("%s",&t);
printf("Generated divisor is :%sn",g);
a=strlen(t);
for(e=a;e<a+N-1;e++)
t[e]='0';
printf("Modified polynomial is %sn",t);
crc( );
printf("Checksum is :%sn",cs);
for(e=a;e<a+N-1;e++)
t[e]=cs[e-a];
printf("Final codeword is %sn",t);
printf("Test error detection?n1(yes) 0(no):n");
scanf("%d",&flag);
if(flag==0)
return;
if(flag==1)
{
printf("Enter position where error is to be inserted:n ");
scanf("%d",&e);
if(e<a+N-1){
t[e]=(t[e]=='0')?'1':'0';
1 | P a g e A n a n d a K u m a r H N

2. Networks Laboratory – 10CSL77 PART - B
printf("err data : %sn",t);
}
else
printf("Position where error should be created is above the length of Codeword...Hencen");
}
crc();
for(e=0;(e<N-1)&&(cs[e]!='1');e++);
if(e<N-1)
printf("Error detectedn");
else
printf("No error detected n");
return;
}
OUTPUT:
2. Write a program for “distance vector algorithm” to find suitable path for
transmission.
#include<stdio.h>
struct node
{
int dist[20];
int from[20];
}rt[10];
int main()
{
int distance_matrix[20][20];
int n,i,j,k,count=0,src,dest;
printf("nEnter the number of nodes : ");
scanf("%d",&n);
printf("nEnter the cost/distance matrix :n");
for(i=0;i<n;i++)
for(j=0;j<n;j++)
{
scanf("%d",&distance_matrix[i][j]);
distance_matrix[i][i]=0;
rt[i].dist[j]=distance_matrix[i][j];
rt[i].from[j]=j;
}
do
{
count=0;
for(i=0;i<n;i++)
for(j=0;j<n;j++)
2 | P a g e A n a n d a K u m a r H N

3. Networks Laboratory – 10CSL77 PART - B
for(k=0;k<n;k++)
if((rt[i].dist[j])>(distance_matrix[i][k]+rt[k].dist[j]))
{
rt[i].dist[j]=rt[i].dist[k]+rt[k].dist[j];
rt[i].from[j]=k;
count++;
}
} while(count!=0);
for(i=0;i<n;i++)
{ printf("n---------------------------------");
printf("nRouting table for router %d :nDesttNextHopttDistn",i+1);
printf("----------------------------------n");
for(j=0;j<n;j++)
printf("%dt%dtt%dn",j+1,rt[i].from[j]+1,rt[i].dist[j]);
}
printf("nEnter source and destination : ");
scanf("%d%d",&src,&dest);
src--; dest--;
if(rt[src].dist[dest]!=999)
printf("Shortest path : n Via router : %dn Shortest distance : %d n",rt[src].from[dest]+1,rt[src].dist[dest]);
else
printf("no connection exists between %d----->%d",src+1,dest+1);
return 0;
}
6. Write a program for congestion control using leaky bucket algorithm.
#include<stdio.h>
#include<math.h>
int random(int a)
{ int rn=(rand()%10)%a;
return rn==0?1:rn;
}
int main()
{
int packet_sz[5],i,clk,b_size,o_rate,p_sz_rm=0,p_sz,p_time;
for(i=0;i<5;++i)
packet_sz[i]=random(6)*10;
for(i=0;i<5;++i)
printf("packet[%d]:%d bytesn",i,packet_sz[i]);
printf("nEnter the Output rate:");
scanf("%d",&o_rate);
printf("Enter the Bucket Size:");
scanf("%d",&b_size);
for(i=0; i<5; ++i)
{
if((packet_sz[i]+p_sz_rm) > b_size)
if(packet_sz[i] > b_size)
printf("nnIncomming packet size (%d) is Greater than bucket capacity-PACKET REJECTED",packet_sz[i]);
else
3 | P a g e A n a n d a K u m a r H N

4. Networks Laboratory – 10CSL77 PART - B
printf("nnPacket[%d] size %d + Packet remaining %d exceeds Bucket capacity - PACKET
REJECTED!!",i+1,packet_sz[i],p_sz_rm);
else
{
p_sz_rm+=packet_sz[i];
printf("nnIncomming Packet size: %d",packet_sz[i]);
printf("nBytes remaining to Transmit: %d",p_sz_rm);
p_time = random(4)*10;
printf("nTime left for transmission: %d units",p_time);
for(clk=10; clk<=p_time; clk+=10)
{
if(p_sz_rm)
{
if(p_sz_rm <= o_rate)
{
printf("n Packet of size %d Transmitted",p_sz_rm);
p_sz_rm=0;
}
else
{
printf("n Packet of size %d Transmitted",o_rate);
p_sz_rm -= o_rate;
printf("nBytes Remaining after Transmission:%d",p_sz_rm);
}
}
else
printf("n No packets to transmit!!");
printf(" Time Left:%d",p_time-clk);
}
}
}
}
4 | P a g e A n a n d a K u m a r H N