Program-1 : OSI Model Simulation

Code :

#include<iostream>
#include<string.h>
#include<stdio.h>
using namespace std;
void transmitter( char* str1)
{ char a[]="AH",b[]="PH",c[]="SH",d[]="TH",e[]="NH",f[]="DH";
strcat(a,str1);
cout<<"Application Layer : "<<a<<"\n";
strcat(b,a);
cout<<"Presentation Layer : "<<b<<"\n";
strcat(c,b);
cout<<"Session Layer : "<<c<<"\n";
strcat(d,c);
cout<<"Transport Layer : "<<d<<"\n";
strcat(e,d);
cout<<"Network Layer : "<<e<<"\n";
strcat(f,e);
cout<<"Datalink Layer : "<<f<<"\n";
cout<<"\nMESSAGE ENTERED INTO PHYSICAL LAYER AND TRANSMITTED.\n";
cout<<"\nRECIEVER\n\n";
cout<<"MESSAGE ENTERED INTO PHYSICAL LAYER\n\n";
cout<<"Datalink Layer : "<<f<<"\n";
cout<<"Network Layer : ";
for(int i=2;i<strlen(f);i++)
cout<<f[i];
cout<<"\nTransport Layer : ";
for(int i=4;i<strlen(f);i++)
cout<<f[i];
cout<<"\nSession Layer : ";
for(int i=6;i<strlen(f);i++)
cout<<f[i];
cout<<"\nPresentation Layer : ";
for(int i=8;i<strlen(f);i++)
cout<<f[i];
cout<<"\nApplication Layer : ";
for(int i=10;i<strlen(f);i++)
cout<<f[i];
}
main()
{ char str[10],add[10];
cout<<"Input String : ";
cin>>str;
cout<<"Input Address : ";
cin>>add;
cout<<"\nTRANSMITTER\n\n";
transmitter(str);
}








PROGRAM-2 : Data link layer framing methods

1. Character count
2. Character stuffing
3. Bit stuffing

1. Character Count :


Code:

#include <stdio.h>
#include <conio.h>
#include <string.h>
void main(){
int size;
int total=0;
int i=1;
int j,k=0;
int fsize;
printf("Enter the no. of characters: ");
scanf("%d",&size);
char str[size];
printf("\nEnter the characters: ");
scanf("%s",&str);
while(k<size)
{
printf("Enter the frame %d size: ",i);
scanf("%d",&fsize);
char frame[fsize+1];
i++;
total+=fsize;
frame[0]=(char)(fsize+48);
for(j=1;j<fsize;j++)
{
if(k<size)
{
printf("%c\n",str[k]);
frame[j]=str[k];
k++;
}
}
frame[fsize]='\0';
printf("%s\n",frame);
}
getch();
}








2. Character Stuffing

Code:

#include<stdio.h>
#include<conio.h>
#include<string.h>
void charc(void);
void main()
{i
nt choice;
while(1)
{p
rintf("\n\n\n1.character stuffing");
printf("\n\n2.exit");
printf("\n\n\nenter choice");
scanf("%d",&choice);
printf("%d",choice);
if(choice>2)
printf("\n\n invalid option....please renter");
switch(choice)
{
case 1:
charc();
break;
case 2:
exit(0);
}}}
void charc(void)
{ char c[50],d[50],t[50];
int i,m,j;
clrscr();
printf("enter the number of characters\n");
scanf("%d",&m);
printf("\n enter the characters\n");
for(i=0;i<m+1;i++)
{
scanf("%c",&c[i]);
}p
rintf("\n original data\n");
for(i=0;i<m+1;i++)
printf("%c",c[i]);
d[0]='d';
d[1]='l';
d[2]='e';
d[3]='s';
d[4]='t';
d[5]='x';
for(i=0,j=6;i<m+1;i++,j++)
{
if((c[i]=='d'&&c[i+1]=='l'&& c[i+2]=='e'))
{d[j]='d';
j++;
d[j]='l';
j++;
d[j]='e';
j++;
m=m+3;
}d
[j]=c[i];
}
m=m+6;
m++;
d[m]='d';
m++;
d[m]='l';
m++;
d[m]='e';
m++;
d[m]='e';
m++;
d[m]='t';
m++;
d[m]='x';
m++;
printf("\n\n transmitted data: \n");
for(i=0;i<m;i++)
{
printf("%c",d[i]);
}f
or(i=6,j=0;i<m-6;i++,j++)
{
if(d[i]=='d'&&d[i+1]=='l'&&d[i+2]=='e'&&d[i+3]=='d'&&d[i+4]=='l'&&d[i+5]=='e
')
i=i+3;
t[j]=d[i];
}p
rintf("\n\nreceived data:");
for(i=0;i<j;i++)
{printf("%c",t[i]);
}}

Output :








3.Bit Stuffing

Code:

#include<stdio.h>
#include<conio.h>
#include<string.h>
void main() {
int i, j,count=0,nl;
char str[100];
clrscr();
printf("enter the bit string: ");
gets(str);
for (i=0;i<strlen(str);i++) {
count=0;
for (j=i;j<=(i+5);j++) {
if(str[j]=='1') {
count++;
}
}
if(count==6) {
nl=strlen(str)+2;
for (;nl>=(i+5);nl--) {
str[nl]=str[nl-1];
}
str[i+5]='0';
i=i+7;
}}
puts(str);
getch();
}
Output:








PROGRAM-3 : To Calculate the Checksum

Code:

#include<stdio.h>
#include<conio.h>
#include<math.h>
int sender(int b[10],int k)
 {
	intchecksum,sum=0,i;
	printf("\n****SENDER****\n");

                       for(i=0;i<k;i++)
		sum+=b[i];
		printf("SUM IS: %d",sum);

	checksum=~sum;
	printf("\nSENDER's CHECKSUM IS:%d",checksum);
	return checksum;
}

int receiver(int c[10],intk,intscheck)
{
intchecksum,sum=0,i;
	printf("\n\n****RECEIVER****\n");
	for(i=0;i<k;i++)
		sum+=c[i];
	printf(" RECEIVER SUM IS:%d",sum);
	sum=sum+scheck;
	checksum=~sum;
	printf("\nRECEIVER's CHECKSUM IS:%d",checksum);
		return checksum;
  }
main()
   {
	int a[10],i,m,scheck,rcheck;
clrscr();
	printf("\nENTER SIZE OF THE STRING:");
	scanf("%d",&m);
	printf("\nENTER THE ELEMENTS OF THE ARRAY:");
	for(i=0;i<m;i++)
	scanf("%d",&a[i]);
	scheck=sender(a,m);
	rcheck=receiver(a,m,scheck);
	if(rcheck==0)
		printf("\n\nNO ERROR IN TRANSMISSION\n\n");
	else
		printf("\n\nERROR DETECTED");
getch();
}







Program-4: Generation and checking of CRC

Code:
#include<stdio.h>
#include<conio.h>
#define N strlen(g)

char t[128], cs[128], g[]="100010000";
int a, e, c;

void xor() {
for(c=1;c}

void crc() {
for(e=0;e do {
if(cs[0]=='1') xor();
for(c=0;c cs[c]=t[e++];
}while(e<=a+N-1);
}

void main() {
clrscr();
printf("\nEnter poly : "); scanf("%s",t);
printf("\nGenerating Polynomial is : %s",g);
a=strlen(t);
for(e=a;e
 printf("\nModified t[u] is : %s",t);
crc();
printf("\nChecksum is : %s",cs);
for(e=a;e printf("\nFinalCodeword is : %s",t);
printf("\nTest Error detection 0(yes) 1(no) ? : ");
scanf("%d",&e);
if(e==0) {
printf("Enter position where error is to inserted : ");
scanf("%d",&e);
t[e]=(t[e]=='0')?'1':'0';
printf("Errorneous data : %s\n",t);
}
crc();
for (e=0;(e<n-1)&&(cs[e]!='1');e++);
 if(e
 else printf("No Error Detected.");
getch();
}







Program-5: Generation of hamming code

Code:
#include<stdio.h>
#include<conio.h>
void main() {
	int data[7],rec[7],i,c1,c2,c3,c;
	printf("this works for message of 4bits in size \nenter message bit one by one:  ");
	scanf("%d%d%d%d",&data[0],&data[1],&data[2],&data[4]);
	data[6]=data[0]^data[2]^data[4];
	data[5]=data[0]^data[1]^data[4];
	data[3]=data[0]^data[1]^data[2];
	printf("\nthe encoded bits are given below: \n");
	for (i=0;i<7;i++) {
		printf("%d ",data[i]);
	}
	printf("\nenter the received data bits one by one: ");
	for (i=0;i<7;i++) {
		scanf("%d",&rec[i]);
	}
	c1=rec[6]^rec[4]^rec[2]^rec[0];
	c2=rec[5]^rec[4]^rec[1]^rec[0];
	c3=rec[3]^rec[2]^rec[1]^rec[0];
	c=c3*4+c2*2+c1 ;
	if(c==0) {
		printf("\ncongratulations there is no error: ");
	} else {
		printf("\nerron on the postion: %d\nthe correct message is \n",c);
		if(rec[7-c]==0)
					rec[7-c]=1; else
					rec[7-c]=0;
		for (i=0;i<7;i++) {
			printf("%d ",rec[i]);
		}
	}
	getch();
}

Output:




Program 6: Sliding Window Protocol




Code:

#include<stdio.h>
#include<stdlib.h>
void main()
{
char sender[50],receiver[50];
inti,winsize;
printf("\n ENTER THE WINDOWS SIZE : ");
scanf("%d",&winsize);
printf("\n SENDER WINDOW IS EXPANDED TO STORE MESSAGE OR WINDOW \n");
printf("\n ENTER THE DATA TO BE SENT: ");

scanf("%s",sender);
for(i=0;i<winsize;i++)
receiver[i]=sender[i];
receiver[i]='\0';
printf("\n MESSAGE SEND BY THE SENDER:\n");
printf("%s",sender);
printf("\n WINDOW SIZE OF RECEIVER IS EXPANDED\n");
printf("\n ACKNOWLEDGEMENT FROM RECEIVER \n");
for(i=0;i<winsize;i++);
printf("\n ACK:%d",i);
printf("\n MESSAGE RECEIVED BY RECEIVER IS : ");
printf("%s",receiver);
printf("\n WINDOW SIZE OF RECEIVER IS SHRINKED \n");
}












Program 7:  Chat Application using TCP/IP



Program:

// Server Program - Communicating to single client multiple number of times
#include<stdio.h>
#include<netinet/in.h>
#include<netdb.h>
#include<string.h>
#define SERV_TCP_PORT 5035
int main(intargc,char**argv)
{
intsockfd,newsockfd,clength;
structsockaddr_inserv_addr,cli_addr;
char buffer[4096];
//creating a socket
sockfd=socket(AF_INET,SOCK_STREAM,0);
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=INADDR_ANY;
serv_addr.sin_port=htons(SERV_TCP_PORT);
printf("\nStart");
//bind the socket to port address and any local interface
bind(sockfd,(structsockaddr*)&serv_addr,sizeof(serv_addr));
printf("\nListening...");
printf("\n");
listen(sockfd,5);
clength=sizeof(cli_addr);
newsockfd=accept(sockfd,(structsockaddr*)&cli_addr,&clength);
//newsockfd=accept(sockfd,(structsockaddr*)NULL,NULL);.
printf("\nAccepted");
printf("\n");
while(1)
{
bzero(buffer,4096);
read(newsockfd,buffer,4096);
printf("\nClient message:%s",buffer);
write(newsockfd,buffer,strlen(buffer)+1);
printf("\n");
}
close(sockfd);
return 0;
}













Client Side:
Client Program - Multiple communications to server
#include<stdio.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<netdb.h>
#define SERV_TCP_PORT 5035
int main(intargc,char*argv[])
{
intsockfd;
structsockaddr_inserv_addr;
structhostent *server;
char buffer[4096];
int k=5,cnt=0;
sockfd=socket(AF_INET,SOCK_STREAM,0);
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=inet_addr("127.0.0.1");
serv_addr.sin_port=htons(SERV_TCP_PORT);
printf("\nReady for sending...");
connect(sockfd,(structsockaddr*)&serv_addr,sizeof(serv_addr));
while(cnt<= k)
{
printf("\nEnter the message to send\n");
printf("\nClient: ");
fgets(buffer,4096,stdin);
write(sockfd,buffer,4096);
printf("Serverecho:%s",buffer);
printf("\n");
cnt++;
}
close(sockfd);
return 0;
}

Screenshot:








8.TCP Client/server application for transferring a text file from client to server.

Fileser.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
int main()
{
int listenfd=0;int connfd=0;
struct sockaddr_in serv_addr;
char sendbuff[1025];
int numrv;
listenfd=socket(AF_INET,SOCK_STREAM,0);
printf("socket retrieve success\n");
memset(&serv_addr,'0',sizeof(serv_addr));
memset(sendbuff,'0',sizeof(sendbuff));
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=htons(INADDR_ANY);
serv_addr.sin_port=htons(5000);
bind(listenfd,(struct sockaddr*)&serv_addr,sizeof(serv_addr));
if(listen(listenfd,10)==-1){
printf("failed to listen\n");
return -1;
}
while(1)
{
connfd=accept(listenfd,(struct sockaddr*)NULL,NULL);

FILE *fp=fopen("sample_file.txt","rb");
if(fp==NULL)
{
printf("file open error");
return 1;
}
while(1)
{
unsigned char buff[256]={0};
int nread=fread(buff,1,256,fp);
printf("bytes read %d \n",nread);
if(nread>0)
{
printf("sending\n");
write(connfd,buff,nread);
}
if(nread<256)
{
if(feof(fp))
printf("end of file\n");
if(ferror(fp))
printf("error reading");
break;
}
}}
close(connfd);
sleep(1);
}


fclient.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
int main(){
int sockfd=0;
int bytesreceived=0;
char recvbuff[256];
memset(recvbuff,'0',sizeof(recvbuff));
struct sockaddr_in serv_addr;
if((sockfd=socket(AF_INET,SOCK_STREAM,0))<0)
{
printf("\nerror:could not create socket\n");
return 1;
}
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(5000);
serv_addr.sin_addr.s_addr=inet_addr("127.0.0.1");
if(connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr))<0)
{
printf("\nerror:connect failed\n");
return 1;
}
FILE *fp;
fp=fopen("sample_file.txt","ab");
if(fp==NULL)
{
printf("error opening file");
return 1;
}
while((bytesreceived=read(sockfd,recvbuff,256))>0)
{
printf("bytes received %d \n",bytesreceived);
recvbuff[bytesreceived]=0;
fwrite(recvbuff,1,bytesreceived,fp);
printf("%s\n",recvbuff);
}
if(bytesreceived<0)
{
printf("\nread error");
}
return 0;
}








9. TCP based server program in C to authenticate the client’s Username and Password

SERVER :
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#define ANSI_COLOR_GREEN "\x1b[32m"
#define ANSI_COLOR_RESET "\x1b[0m"
struct user {
char *username;
char *password;
};
int main() {
/*login details*/
struct user singleUser;
singleUser.username = "omijn";
singleUser.password = "qwerty";
/*messages*/
char * userOK_enterPass = "Please enter your password : ";
char * userNotFound = "This username does not exist.";
char * userAuthenticated = "User authenticated!";
char * invalidPassword = "Invalid password.";
/*errors*/
int bindError = 0;
int serverSocketFD = 0, clientFD = 0, n = 0, auth = 0;
char receiveBuffer[1024] = "", sendBuffer[1024] = "";
struct sockaddr_in serverAddress;
system("clear");
//create socket
if((serverSocketFD = socket(AF_INET, SOCK_STREAM, 0)) == -1)
printf("> Socket creation failed.\n");
else
printf("> Socket created.\n");
//clear memory
memset(receiveBuffer, '0', sizeof(receiveBuffer));
memset(sendBuffer, '0', sizeof(sendBuffer));
memset(&serverAddress, '0', sizeof(serverAddress));
//server address
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(2884);
serverAddress.sin_addr.s_addr = htonl(INADDR_ANY);
printf("> Address created.\n");
//assign name to server
if((bind(serverSocketFD, (struct sockaddr*)&serverAddress,
sizeof(serverAddress))) == -1) {
printf("> Bind error.\n");
bindError = errno;
printf("%s\n", strerror(bindError));
return -1;
}
else
printf("> Binding successful.\n");
//listen
if((listen(serverSocketFD, 5)) == -1)
printf("> Listen error.\n");
else
printf("> Server listening.\n");
//accept connection
if((clientFD = accept(serverSocketFD, (struct sockaddr *)NULL,
NULL)) != 0)
printf(ANSI_COLOR_GREEN "> Client connected!\n"
ANSI_COLOR_RESET);
else
printf("> Client connect error.\n");
while(!auth) {
/* receive
-------------------------------------------------------------------
*/
while((n = read(clientFD, receiveBuffer,
sizeof(receiveBuffer) - 1)) > 0) {
if(n == -1)
printf("> Read error.\n");
receiveBuffer[n] = 0;
break;
}
if(strcmp(receiveBuffer, singleUser.username) == 0) {
write(clientFD, userOK_enterPass, strlen(userOK_enterPass));
auth = 0;
while(!auth) {
while((n = read(clientFD, receiveBuffer, sizeof(receiveBuffer) - 1))
> 0) {
if(n == -1)
printf("> Read error.\n");
receiveBuffer[n] = 0;
break;
}
if(strcmp(receiveBuffer, singleUser.password) == 0) {
/*user authenticated*/
auth = 1;
printf("\n%s", userAuthenticated);
write(clientFD, userAuthenticated,
strlen(userAuthenticated));
}
else {
auth = 0;
printf("\n%s", invalidPassword);
write(clientFD, invalidPassword,
strlen(invalidPassword));
}
}
}
else {
printf("\n%s", userNotFound);
write(clientFD, userNotFound, strlen(userNotFound));
}
printf(ANSI_COLOR_GREEN "\n%s" ANSI_COLOR_RESET,
receiveBuffer);
//clear receive buffer for next use
strcpy(receiveBuffer, "");
//clear send buffer for next use
strcpy(sendBuffer, "");
}
printf("\n");
return 0;
}


CLIENT :

#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#define ANSI_COLOR_GREEN "\x1b[32m"
#define ANSI_COLOR_RESET "\x1b[0m"
struct user {
char *username;
char *password;
};
int main() {
/*login details*/
struct user singleUser;
singleUser.username = "omijn";
singleUser.password = "qwerty";
/*messages*/
char * userOK_enterPass = "Please enter your password : ";
char * userNotFound = "This username does not exist.";
char * userAuthenticated = "User authenticated!";
char * invalidPassword = "Invalid password.";
/*errors*/
int bindError = 0;
int serverSocketFD = 0, clientFD = 0, n = 0, auth = 0;
char receiveBuffer[1024] = "", sendBuffer[1024] = "";
struct sockaddr_in serverAddress;
system("clear");
//create socket
if((serverSocketFD = socket(AF_INET, SOCK_STREAM, 0)) == -1)
printf("> Socket creation failed.\n");
else
printf("> Socket created.\n");
//clear memory
memset(receiveBuffer, '0', sizeof(receiveBuffer));
memset(sendBuffer, '0', sizeof(sendBuffer));
memset(&serverAddress, '0', sizeof(serverAddress));
//server address
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(2884);
serverAddress.sin_addr.s_addr = htonl(INADDR_ANY);
printf("> Address created.\n");
//assign name to server
if((bind(serverSocketFD, (struct sockaddr*)&serverAddress,
sizeof(serverAddress))) == -1) {
printf("> Bind error.\n");
bindError = errno;
printf("%s\n", strerror(bindError));
return -1;
}
else
printf("> Binding successful.\n");
//listen
if((listen(serverSocketFD, 5)) == -1)
printf("> Listen error.\n");
else
printf("> Server listening.\n");
//accept connection
if((clientFD = accept(serverSocketFD, (struct sockaddr *)NULL,
NULL)) != 0)
printf(ANSI_COLOR_GREEN "> Client connected!\n"
ANSI_COLOR_RESET);
Else
printf("> Client connect error.\n");
while(!auth) {
/* receive
-------------------------------------------------------------------
*/
while((n = read(clientFD, receiveBuffer,
sizeof(receiveBuffer) - 1)) > 0) {
if(n == -1)
printf("> Read error.\n");
receiveBuffer[n] = 0;
break;
}
if(strcmp(receiveBuffer, singleUser.username) == 0) {
write(clientFD, userOK_enterPass, strlen(userOK_enterPass));
auth = 0;
while(!auth) {
while((n = read(clientFD, receiveBuffer, sizeof(receiveBuffer) - 1)) > 0) {
if(n == -1)
printf("> Read error.\n");
receiveBuffer[n] = 0;
break;
}
if(strcmp(receiveBuffer, singleUser.password) == 0) {
/*user authenticated*/
auth = 1;
printf("\n%s", userAuthenticated);
write(clientFD, userAuthenticated,
strlen(userAuthenticated));
}
else {
auth = 0;
printf("\n%s", invalidPassword);
write(clientFD, invalidPassword,
strlen(invalidPassword));
}
}
}
else {
printf("\n%s", userNotFound);
write(clientFD, userNotFound, strlen(userNotFound));
}
printf(ANSI_COLOR_GREEN "\n%s" ANSI_COLOR_RESET,
receiveBuffer);
//clear receive buffer for next use
strcpy(receiveBuffer, "");
//clear send buffer for next use
strcpy(sendBuffer, "");
}
printf("\n");
return 0;
}










Ques 10:---  Implement a message transfer from client to server process using UDP

Code:--

Server:-


#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <stdlib.h>

int main(){
  int udpSocket, nBytes;
  char buffer[1024];
  struct sockaddr_in serverAddr, clientAddr;
  struct sockaddr_storage serverStorage;
  socklen_t addr_size, client_addr_size;
  int i;

  /*Create UDP socket*/
  udpSocket = socket(PF_INET, SOCK_DGRAM, 0);

  /*Configure settings in address struct*/
  serverAddr.sin_family = AF_INET;
  serverAddr.sin_port = htons(7891);
  serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);

  /*Bind socket with address struct*/
  bind(udpSocket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));

  /*Initialize size variable to be used later on*/
  addr_size = sizeof serverStorage;

  while(1){
    /* Try to receive any incoming UDP datagram. Address and port of
      requesting client will be stored on serverStorage variable */
    nBytes = recvfrom(udpSocket,buffer,1024,0,(struct sockaddr *)&serverStorage, &addr_size);

    /*Convert message received to uppercase*/
    for(i=0;i<nBytes-1;i++)
      buffer[i] = toupper(buffer[i]);

    /*Send uppercase message back to client, using serverStorage as the address*/
    sendto(udpSocket,buffer,nBytes,0,(struct sockaddr *)&serverStorage,addr_size);
  }

  return 0;
}



Output

Server















Code:-

Client :-

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main(){
  int clientSocket, portNum, nBytes;
  char buffer[1024];
  struct sockaddr_in serverAddr;
  socklen_t addr_size;

  /*Create UDP socket*/
  clientSocket = socket(PF_INET, SOCK_DGRAM, 0);

  /*Configure settings in address struct*/
  serverAddr.sin_family = AF_INET;
  serverAddr.sin_port = htons(7891);
  serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);

  /*Initialize size variable to be used later on*/
  addr_size = sizeof serverAddr;

  while(1){
    printf("Type a sentence to send to server:\n");
    fgets(buffer,1024,stdin);
    printf("You typed: %s",buffer);

    nBytes = strlen(buffer) + 1;

    /*Send message to server*/
    sendto(clientSocket,buffer,nBytes,0,(struct sockaddr *)&serverAddr,addr_size);

    /*Receive message from server*/
                nBytes = recvfrom(clientSocket,buffer,1024,0,NULL, NULL);

    printf("Received from server: %s\n",buffer);

  }

  return 0;
}






Output





AIM: To write a program for UDP echo client server.
CODE :
SERVER:
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<unistd.h>
#include<netdb.h>
#include<stdio.h>
#include<string.h>
#include<arpa/inet.h>
#define MAXLINE 1024
int main(int argc,char **argv)
{
int sockfd;
int n;
socklen_t len;
char msg[1024];
struct sockaddr_in servaddr,cliaddr;
sockfd=socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_addr.s_addr=INADDR_ANY;
servaddr.sin_port=htons(5035);
printf("\n\n Binded");
bind(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
printf("\n\n Listening...");
for(;;)
{
 printf("\n ");
 len=sizeof(cliaddr);
 n=recvfrom(sockfd,msg,MAXLINE,0,(struct
sockaddr*)&cliaddr,&len);
 printf("\n Client's Message : %s\n",msg);
 if(n<6)
 perror("send error");
 sendto(sockfd,msg,n,0,(struct sockaddr*)&cliaddr,len);
}
return 0;
}
CLIENT:
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<string.h>
#include<arpa/inet.h>
#include<string.h>
#include<arpa/inet.h>
#include<stdio.h>
#define MAXLINE 1024
int main(int argc,char* argv[])
{
int sockfd;
int n;
socklen_t len;
char sendline[1024],recvline[1024];
struct sockaddr_in servaddr;
strcpy(sendline,"");
printf("\n Enter the message : ");
scanf("%s",sendline);
sockfd=socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_addr.s_addr=inet_addr("127.0.0.1");
servaddr.sin_port=htons(5035);
connect(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
len=sizeof(servaddr);
sendto(sockfd,sendline,MAXLINE,0,(struct sockaddr*)&servaddr,len);
n=recvfrom(sockfd,recvline,MAXLINE,0,NULL,NULL);
recvline[n]=0;
printf("\n Server's Echo : %s\n\n",recvline);
return 0;
}
OUTPUT