CS 372
Computer Networks
Assignment #3
Submitted by:
Ashish Gupta , 98131
Ravi Krishna , 98422
Description
In this assignment , we were told to develop a series of programs based
on socket programming using both TCP and UDP protocol.
7 programs were developed in this assignment
1. TCP Echo Client
2. UDP Echo Client
3. TCP Echo Server
4. UDP Echo Server
5. UDP Date Client
6. TCP/UDP Echo Server using I/O Multiplexing
7. A TCP based client/server system consisting of a server which
responds to multiple clients and allows them to issue "ls" and "more" commands
to view the directory information and view a file on the server machine.
Logical Steps in assignment
1. TCP Echo Client
In the TCP Echo client a socket is created. Using the socket a connection is made to the server using the connect() function. After a connection is established , we send messages input from the user and display the data received from the server using send() and read() functions.
2. UDP Echo Client
In the UDP Echo client a socket is created. Then we bind the socket. After the binding is succesful , we send messages input from the user and display the data received from the server using sendto() and recvfrom() functions.
3. TCP Echo Server
In the TCP Echo server , we create a socket and bind to a advertized port number. After binding , the process listens for incoming connections. Then an infinite loop is started to process the client requests for connections. After a connection is requested , it accepts the connection from the client machine and forks a new process. The new process receives data from the client using recv() function and echoes the same data using the send() function. Please note that this server is capable of handling multiple clients as it forks a new process for every client trying to connect to the server.
4. UDP Echo Server
In the UDP Echo server , we create a socket and bind to a advertized port number. Then an infinite loop is started to process the client requests for connections. The process receives data from the client using recvfrom () function and echoes the same data using the sendto() function. Please note that this server is capable of handles multiple clients automatically as UDP is a datagram based protocol hence no exclusive connection is required to a client in this case.
5. UDP Date Client
In the UDP Date client a socket is created. Then we bind the socket. After the binding is succesful , we send an arbitrary datagram to port 13 on the server machine and then display the datagram received which is supposed to be the data/time on the server.
6. TCP/UDP Echo Server using I/O Multiplexing
We have used the concept of I/O multiplexing for managing both TCP
and UDP port in the same server.
fd_set fdvar;
FD_ZERO(&fdvar);
FD_SET(tcp_sfd,&fdvar);
FD_SET(udp_sfd,&fdvar);
int maxpl = max(tcp_sfd,udp_sfd);
cout << "Waiting for
a client...\n";
if(select(maxpl+2 ,&fdvar,NULL,NULL,NULL)==-1)
{
perror("error in select");
}
if(FD_ISSET(udp_sfd,&fdvar))
{
// UDP
}
else
{
//TCP
}
struct fd_set can be set to monitor activity
on many ports at the same time.
FD_SET(tcp_sfd,&fdvar) sets the appropriate
bit in fdvar so that select may monitor tcp_sfd
similarly FD_SET(udp_sfd,&fdvar)
sets the appropriate bit in fdvar so that select may monitor
the udp_sfd.
We use select system call to monitor socket fd's
for TCP & UDP servers which are
listening to the same port
ie. port 3001
FD_ISSET checks which sfd has received a packet.
Once this is known we handle the request as in case
of TCP client or UDP client
7. A TCP based client/server system
In this part of the assignment we have proceeded on the lines of TCP Echo Server / Echo Client.
We create a TCP Server which listens for various TCP Clients trying
to connect to the server.
Once a client connects we start a new process which deals with that
particular client.
It receives the message from the client and breaks it into various
tokes seperated by space.
It then analyses the arguments for "ls" and "cat" command otherwise
it returns a default message.