Server/Client Go-Back-N

crazystudentc · 10-24-2012, 04:51 AM

Hi, I have a little side project I have to do, but for the life of me I cant figure out the information.

Ive got the following two source codes

Server1.c

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>


#define MYPORT "4951"	

// This is the size of our receiving buffer
#define MAXBUFLEN 100


int main(void)
{
	int       sockfd;
	struct addrinfo hints, *servinfo, *p;
	int       rv;
	int       numbytes;
	struct    sockaddr_storage their_addr;
	char      buf[MAXBUFLEN];
	socklen_t addr_len;

        
	memset(&hints, 0, sizeof hints);
	hints.ai_family   = AF_UNSPEC;  
	hints.ai_socktype = SOCK_DGRAM;
	hints.ai_flags    = AI_PASSIVE; 

        // COMMENT -- What does the following function do?
        // COMMENT -- Why is the first parameter to getaddrinfo NULL?
	if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
		return 1;
	}

	
	for(p = servinfo; p != NULL; p = p->ai_next) 
        {
		if ((sockfd = socket(p->ai_family, p->ai_socktype,
				p->ai_protocol)) == -1) {
			perror("listener: socket");
			continue;
		}

		if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
			close(sockfd);
			perror("listener: bind");
			continue;
		}

		break;
	} // END FOR

	if (p == NULL) {
		fprintf(stderr, "listener: failed to bind socket\n");
		return 2;
	}

	freeaddrinfo(servinfo);

	printf("server: waiting to recvfrom...\n");

 
    
      while(1) 
      {
	
	addr_len = sizeof their_addr;
	if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
		(struct sockaddr *)&their_addr, &addr_len)) == -1) 
        {
		perror("recvfrom");
		exit(1);
	}

        
	buf[numbytes] = '\0';
	printf("server: received... \"%s\"\n", buf);

       
   

       } // END WHILE -- the main loop

      //  -----------------------------------------------------------------------
      // Close the socket to the channel.
      close(sockfd);

      return 0;
}

and client1.c

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>

// The channel's port
#define CHANNELPORT "4950"
// Our receiving buffer length
#define MAXBUFLEN   100
// Size of our frame
#define MAXMESGLEN  1

int main(int argc, char *argv[])
{
	int sockfd;                          
	struct addrinfo hints, *servinfo, *p; 
	int rv;                               
	int numbytes;                         
        socklen_t addr_len;                   
        struct sockaddr_storage their_addr;   

        char buf[MAXBUFLEN];                  
        char myframe[MAXMESGLEN];             

        char *mesg = "A";                     // Message to be sent

        
        fd_set fds;
        int rc;
        struct timeval timeout;


     
	memset(&hints, 0, sizeof hints);
	hints.ai_family   = AF_UNSPEC;        
	hints.ai_socktype = SOCK_DGRAM;      

        
	if ((rv = getaddrinfo("127.0.0.1", CHANNELPORT, &hints, &servinfo)) != 0) {
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
		return 1;
	}

	
	for(p = servinfo; p != NULL; p = p->ai_next) 
        {
		if ((sockfd = socket(p->ai_family, p->ai_socktype,
				p->ai_protocol)) == -1) {
			perror("client: socket");
			continue;
		}

		break;
	}

       
	if (p == NULL) {
		fprintf(stderr, "client: failed to bind socket\n");
		return 2;
	}

        myframe[0] = mesg[0];

      
	if ((numbytes = sendto(sockfd, myframe, MAXMESGLEN, 0,
		               p->ai_addr, p->ai_addrlen)) == -1) 
        {
		perror("talker: sendto");
		exit(1);
	}

        printf("Done Sending: %d\n", numbytes);

     
	freeaddrinfo(servinfo);
	close(sockfd);
	return 0;
}

Basically I have this code compiled, all works, Im using IdealChannel and EvilChannel, which are two channels im meant to test things on.

In My first step which im stuck on, is I need to modify the above codes to include Go-Back-N. I have to transfer the letters in the char *mesg = "A", and I also have to edit char* mesg so it send a string of ABCD, but sending one letter at a time, and transfer the letters using go-back-n as well.

I was wondering how exactly am I supposed to do that, and how do I then calculate the average round Trip Time of the channel.

I really want to understand this, as then it will help me in the future with my actaul assignments as i know similar things will be coming up soon.

Regards

crazystudentc · 10-24-2012, 07:55 AM

I have modified client.c to send a large string, but the rest so far i have problems with

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>

// The channel's port -- do not change
#define CHANNELPORT "4950"
// Our receiving buffer length
#define MAXBUFLEN   100
// Size of our frame
#define MAXMESGLEN  1

int main(int argc, char *argv[])
{
	int sockfd;                           
	struct addrinfo hints, *servinfo, *p; 
	int rv;                               
	int numbytes;                         
        socklen_t addr_len;                   
        struct sockaddr_storage their_addr;   

        char buf[MAXBUFLEN];                  
        char myframe[MAXMESGLEN];             

        char *mesg = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123";                     
	int i;

        // used for select
        fd_set fds;
        int rc;
        struct timeval timeout;


	memset(&hints, 0, sizeof hints);
	hints.ai_family   = AF_UNSPEC;        // COMMENT
	hints.ai_socktype = SOCK_DGRAM;       // COMMENT

	if ((rv = getaddrinfo("127.0.0.1", CHANNELPORT, &hints, &servinfo)) != 0) {
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
		return 1;
	}

	// COMMENT
	for(p = servinfo; p != NULL; p = p->ai_next) 
        {
		if ((sockfd = socket(p->ai_family, p->ai_socktype,
				p->ai_protocol)) == -1) {
			perror("client: socket");
			continue;
		}

		break;
	}

        // If we can't get a socket ...
	if (p == NULL) {
		fprintf(stderr, "client: failed to bind socket\n");
		return 2;
	}

     
	for(i=0;i<30;i++)        
	{
		myframe[0] = mesg[i];

       		// COMMENT
		if ((numbytes = sendto(sockfd, myframe, MAXMESGLEN, 0,
		               p->ai_addr, p->ai_addrlen)) == -1) 
        	{
			perror("talker: sendto");
			exit(1);
		}	

        	printf("Done Sending: %d\n", numbytes);
	}
        
      
	freeaddrinfo(servinfo);
	close(sockfd);
	return 0;
}