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1. LAB #19
Ques1:Discuss the concepts of I/O Multiplexing?
Ans1: There were problemswith previous echo client
example,like:
1. Client was blocked in fgets.
2. It was able to see FIN when sent by the server.
3. Only detected server close when called read.
Problems were resolved by I/O multiplexingusing Select
and Poll functions.
Ques2: What are the I/O Models. Discuss it.
Ans2: There are five I/O models that we are going to talk
about:
a.) Blocking i/o:
 All example we have seen so far.
 This is default for sockets.

2. b.) Non blocking i/o:
 Don’t put process to sleep
 return error instead.
 Need to check periodically.
 Waste of CPU.
c.) I/O Multiplexing:
With i/o multiplexing , we call select or poll and
block in one of these two system calls, instead of
blocking in the actual I/O system call.

3. d.) Signal driven i/o:
The signal driven i/o model uses signals, telling the
kernel to notify us with the SIGIO signal when the
descriptor is ready.
e.) Asynchronous i/o:

4. Asynchronous i/o is defined by the POSIX specification,
and various differences in the real-time functions that
appeared in the various standards which came together to
form the current POSIX specification have been
reconciled.
Ques3.Comparedifferent types of I/O Models.
Ans3:
Second phase in allof the first four models is same the
difference is in first phase.First four are synchronousi/o and
the last one is asynchronous.Difference between both is that
synchronousi/o operation causes the requesting process to be
blocked util that i/o operation completes whereas in
asynchronousi/o operationdoes not cause the requesting
process to be blocked.

5. The diagram below show the differences between all five:
Ques4-What are the concepts of select and poll
function.
Ans4-
Select():-
This function allowsthe process to instruct the kernel to wait
for any one of multiple events to occur and to wake up the
process only when one or more of these events occurs or when
a specified amount of time has passed.

6. Poll():- This function was originated with SVR3 and was
originallylimited to stream devices.it is same as select() except
it provides additionfunctionalitiesin case of stream devices.
Ques5:Designa TCP concurrent server to convert a given
text into upper case using multiplexing system call
“select”.
Ans5.
Ans-> #include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <fcntl.h>
#define MAXBUFFER 1024
void sendstring(int , char *);
int main( int C, char *V[] ) {
int sd,fd; char c;
struct sockaddr_in serveraddress;
char text[100] ; int i=0;
sd = socket( AF_INET, SOCK_STREAM, 0 );
if( sd < 0 ) {
perror( "socket" );

7. exit( 1 ); }
if (V[1] == NULL ) {
printf ("PL specfiy the server's IP Address n");
exit(0); }
if (V[2] == NULL ) {
printf ("PL specify the server's Port No n");
exit(0); }
memset( &serveraddress, 0, sizeof(serveraddress) );
serveraddress.sin_family = AF_INET;
serveraddress.sin_port = htons(atoi(V[2]));//PORT NO
serveraddress.sin_addr.s_addr = inet_addr(V[1]);//ADDRESS
if (connect(sd,(struct sockaddr*)&serveraddress,
sizeof(serveraddress))<0) {
printf("Cannot Connect to server");
exit(1); }
printf("enter sentence to end enter #");
while(1) {
c=getchar();
if(c=='#')
break;
text[i++]=c; }
text[i]='0';
sendstring(sd,text);
close(sd);
return 0; }
void sendstring(

8. int sd, /*Socket Descriptor*/
char *fname) /*Array Containing the string
{ int n , byteswritten=0 , written ;
char buffer[MAXBUFFER];
strcpy(buffer , fname);
n=strlen(buffer);
while (byteswritten<n)
{ written=write(sd , buffer+byteswritten,(n-byteswritten));
byteswritten+=written; }
printf("String : %s sent to server n",buffer);
/*TCP SERVER_SELECT*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>>
#include <fcntl.h>
#define MAXLINE 100
#define SERV_PORT 13153
int main(int argc, char **argv)
{ int k, i, maxi, maxfd, listenfd, connfd, sockfd;
int nready, client[FD_SETSIZE];

9. ssize_t n;
fd_set rset, allset;
char line[MAXLINE],buf[100];
socklen_t clilen;
struct sockaddr_in cliaddr, servaddr;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
if (listenfd < 0 ) {
perror("socket" );
exit(1); }
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(SERV_PORT);-
listen(listenfd,5);
maxfd = listenfd; /* initialize */
maxi = -1; /* index into client[] array */
for (i = 0; i < FD_SETSIZE; i++)
client[i] = -1; /* -1 indicates available entry */
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
for ( ; ; ) {
printf("Server:I am waiting-----Start of Main Loopn");
rset = allset; /* structure assignment */
nready = select(maxfd+1, &rset, NULL, NULL, NULL);
if (FD_ISSET(listenfd, &rset)) {
clilen = sizeof(cliaddr);

10. connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &clilen);
#ifdef NOTDEF
printf("new client: %s, port %dn",inet_ntop(AF_INET,
&cliaddr.sin_addr, buf, NULL),ntohs(cliaddr.sin_port));
#endif
for (i = 0; i < FD_SETSIZE; i++)
if (client[i] < 0) {
client[i] = connfd; /* save descriptor */
break;}
if (i == FD_SETSIZE) {
printf("too many clients");
exit(0); }
FD_SET(connfd, &allset);
if (connfd > maxfd)
maxfd = connfd;
if (i > maxi)
maxi = i;
if (--nready <= 0)
continue;}
for (i = 0; i <= maxi; i++) {
if ( (sockfd = client[i]) < 0)
continue;
if (FD_ISSET(sockfd, &rset)) {
if ( (n = read(sockfd, line, MAXLINE)) == 0) {
close(sockfd);
FD_CLR(sockfd, &allset);

11. client[i] = -1;
} else{
printf("n output at servern");
for(k=0;line[k]!='0';k++)
printf("%c",toupper(line[k]));
write(sockfd, line, n);}
if (--nready <= 0)
break; } }}}
Ques6:esign using poll client server application to
multiplex TCP and UDP requests for converting a given
text into upper case.
Ans6:
#include<string.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<netinet/in.h>#include<string.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<netinet/in.h>
#define MAXLINE 20
#define SERV_PORT 8114
main(int argc,char **argv){
int maxfdp1; fd_set rset;
char sendline[MAXLINE],recvline[MAXLINE];
int sockfd;

12. struct sockaddr_in servaddr;
if(argc!=2){
printf("usage tcpcli <ipaddress>"); return;}
sockfd=socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(SERV_PORT);
inet_pton(AF_INET,argv[1],&servaddr.sin_addr);
connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
printf("nenter data to be send:");
while(fgets(sendline,MAXLINE,stdin)!=NULL){
write(sockfd,sendline,MAXLINE);
printf("nline send to server :%s ",sendline);
read(sockfd,recvline,MAXLINE);
printf("line received from the server : %s",recvline);}
exit(0);}
#include<stdio.h>
#include<netinet/in.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/select.h>
#include<unistd.h>
#define MAXLINE 20
#define SERV_PORT 8114
main(int argc,char **argv){
int i,j,maxi,maxfd,listenfd,connfd,sockfd;
int nready,client[FD_SETSIZE]; ssize_t n;

13. fd_set rset,allset; char line[MAXLINE];
socklen_t clilen; struct sockaddr_in cliaddr,servaddr;
listenfd=socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_addr.s_addr=htonl(INADDR_ANY );
servaddr.sin_port=htons(SERV_PORT);
bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
listen(listenfd,1);
maxfd=listenfd;
maxi=-1;
for(i=0;i<FD_SETSIZE;i++)
client[i]=-1;
FD_ZERO(&allset);
FD_SET(listenfd,&allset);
for(;;){
rset=allset;
nready=select(maxfd+1,&rset,NULL,NULL,NULL);
if(FD_ISSET(listenfd,&rset)){
clilen=sizeof(cliaddr);
connfd=accept(listenfd,(struct sockaddr *)&cliaddr,&clilen);
for(i=0;i<FD_SETSIZE;i++)
if(client[i]<0){
client[i]=connfd;
break;}
if(i==FD_SETSIZE){
printf("too many clients");
exit(0);}

14. FD_SET(connfd,&allset);
if(connfd>maxfd)
maxfd=connfd;
if(i>maxi)
maxi=i;
if(--nready<=0)
continue;}
for(i=0;i<=maxi;i++) {
if((sockfd=client[i])<0)
continue;
if(FD_ISSET(sockfd,&rset)){
if((n=read(sockfd,line,MAXLINE))==0){
close(sockfd);
FD_CLR(sockfd,&allset);
client[i]=-1;}
else{{
printf("line received from client:%sn",line);
for(j=0;line[j]!='0';j++)
line[j]=toupper(line[j]);
write(sockfd,line,MAXLINE);}
if(--nready<=0) break;} } } }
#define MAXLINE 20
#define SERV_PORT 8114
main(int argc,char **argv){
int maxfdp1; fd_set rset;
char sendline[MAXLINE],recvline[MAXLINE];
int sockfd;
struct sockaddr_in servaddr;

15. if(argc!=2){
printf("usage tcpcli <ipaddress>"); return;}
sockfd=socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(SERV_PORT);
inet_pton(AF_INET,argv[1],&servaddr.sin_addr);
connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
printf("nenter data to be send:");
while(fgets(sendline,MAXLINE,stdin)!=NULL){
write(sockfd,sendline,MAXLINE);
printf("nline send to server :%s ",sendline);
read(sockfd,recvline,MAXLINE);
printf("line received from the server : %s",recvline);}
exit(0);}
#include<stdio.h>
#include<netinet/in.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/select.h>
#include<unistd.h>
#define MAXLINE 20
#define SERV_PORT 8114
main(int argc,char **argv){
int i,j,maxi,maxfd,listenfd,connfd,sockfd;

16. int nready,client[FD_SETSIZE]; ssize_t n;
fd_set rset,allset; char line[MAXLINE];
socklen_t clilen; struct sockaddr_in cliaddr,servaddr;
listenfd=socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
servaddr.sin_port=htons(SERV_PORT);
bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
listen(listenfd,1);
maxfd=listenfd;
maxi=-1;
for(i=0;i<FD_SETSIZE;i++)
client[i]=-1;
FD_ZERO(&allset);
FD_SET(listenfd,&allset);
for(;;){
rset=allset;
nready=select(maxfd+1,&rset,NULL,NULL,NULL);
if(FD_ISSET(listenfd,&rset)){
clilen=sizeof(cliaddr);
connfd=accept(listenfd,(struct sockaddr *)&cliaddr,&clilen);
for(i=0;i<FD_SETSIZE;i++)
if(client[i]<0){
client[i]=connfd;
break;}

17. if(i==FD_SETSIZE){
printf("too many clients");
exit(0);}
FD_SET(connfd,&allset);
if(connfd>maxfd)
maxfd=connfd;
if(i>maxi)
maxi=i;
if(--nready<=0)
continue;}
for(i=0;i<=maxi;i++) {
if((sockfd=client[i])<0)
continue;
if(FD_ISSET(sockfd,&rset)){
if((n=read(sockfd,line,MAXLINE))==0){
close(sockfd);
FD_CLR(sockfd,&allset);
client[i]=-1;}
else{{
printf("line received from client:%sn",line);
for(j=0;line[j]!='0';j++)
line[j]=toupper(line[j]);
write(sockfd,line,MAXLINE);}
if(--nready<=0) break;} } } }