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1. Introduction

2.Elements of Client Server Computing3.TCP Socket

4.TCP Sockets• Implementing a Client• Implementing a Server•Sample Examples

5.Conclusion

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• Internet and WWW have emerged as globalubiquitous media for communication and

changing the way we conduct science,engineering, and commerce.

•They also changing the way we learn, live,enjoy, communicate, interact, engage, etc.It appears like the modern life activitiesare getting completely centered aroundthe Internet.

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a client, a server, and network 

Client machine

Server machine

Network 

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• A socket is one end-point of a two-way

communication link between two programs

running on the network.

• A server application normally listens to a

specific port waiting for connection requests

from a client. When a connection request

arrives, the client and the server establish adedicated connection over which they can

communicate.

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• During the connection process, the client is

assigned a local port number, and binds

a socket to it. The client talks to the server bywriting to the socket and gets information from

the server by reading from it. Similarly, the

server gets a new local port number (it needs a

new port number so that it can continue to

listen for connection requests on the originalport).

• The server also binds a socket to its local port

and communicates with the client by reading

from and writing to it.

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After initialization, a SOCKET object must be instantiated for useby the client.

• These are the steps to follow:

1. Create a socket with the socket() system call.

// Create a SOCKET for connecting to server 

ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,

ptr->ai_protocol);

// Error message for an Invalid Socket if (ConnectSocket == INVALID_SOCKET)

{

printf("socket failed with error: %ld\n", WSAGetLastError());

WSACleanup();

system("pause");

return 1;} 

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2. Connect the socket to the address of the server using theconnect() socket call.

// Connect to server. iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);

// Socket Error 

if (iResult == SOCKET_ERROR)

{closesocket(ConnectSocket);ConnectSocket = INVALID_SOCKET;continue;

}

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3. Send data from the user and to the server.

//GET THE DATA FROM THE USER 

printf(" Enter Data to send or EXIT : ");

scanf("%s", sendbuf); 

//SEND THE DATA TO THE SERVER 

iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );printf("Bytes Sent: %ld\n", iResult);

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4. Receive the data from the user and to the server.

///Start Receive////

iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);

if ( iResult > 0 )

printf("Bytes received: %d %s\n", iResult, recvbuf);

else if ( iResult == 0 )

printf("Connection closed\n");

elseprintf("recv failed with error: %d\n", WSAGetLastError());

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5. Shutdown of the program

// shutdown the connection since no more data will be sent iResult = shutdown(ConnectSocket, SD_SEND);if (iResult == SOCKET_ERROR)

{printf("shutdown failed with error: %d\n", WSAGetLastError());closesocket(ConnectSocket);

WSACleanup();system("pause");return 1;

}

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• To allow the server to handle multiple simultaneous connections,we make the following changes in the above code:

•

Put the accept statement and the following code in an infiniteloop.

• After a connection is established, call  fork() to create a newprocess.

• The child process will close sockfd and call doprocessing function,passing the new socket file descriptor as an argument. When the

two processes have completed their conversation, as indicatedby doprocessing() returning, this process simply exits.

• The parent process closes newsockfd . Because all of this code isin an infinite loop, it will return to the accept statement to waitfor the next connection.

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• These are the steps to follow to connect with the server:

1. Create a socket with the socket() system call.

// Create a SOCKET for connecting to server

ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);

// Error for an Invalid Socket 

if (ListenSocket == INVALID_SOCKET)

{printf("socket failed with error: %ld\n", WSAGetLastError());

freeaddrinfo(result);

WSACleanup();

system("pause");

return 1;

}

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2. Bind the socket to an address using the bind() system call. Fora server socket on the Internet, an address consists of a portnumber on the host machine.

// Setup the TCP listening socket and Error message

iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);

if (iResult == SOCKET_ERROR) {

printf("bind failed with error: %d\n", WSAGetLastError());

freeaddrinfo(result);closesocket(ListenSocket);

WSACleanup();

system("pause");

return 1;

}

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3. Listen for connections with the listen() system call.

///Listen Socket and Error message

iResult = listen(ListenSocket, SOMAXCONN);

if (iResult == SOCKET_ERROR)

{

printf("listen failed with error: %d\n", WSAGetLastError());

closesocket(ListenSocket);WSACleanup();

system("pause");

return 1;

}

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4. Accept a connection with the accept() system call. This calltypically blocks until a client connects with the server.

// Accept a client socket and Error messageClientSocket = accept(ListenSocket, NULL, NULL);

if (ClientSocket == INVALID_SOCKET)

{

printf("accept failed with error: %d\n", WSAGetLastError());

closesocket(ListenSocket);WSACleanup();

system("pause");

return 1;

}

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5. Send and receive data using the read(), and write() systemcalls.// Receive until the peer shuts down the connection

do {

// RECEIVE MESSAGE FROM THE CLIENTiResult = recv(ClientSocket, recvbuf, recvbuflen, 0);

//Do a string comparison

//If receive buff = exit set iResult to 0

if( strcmp(recvbuf, "EXIT")==0)

iResult = 0;if (iResult > 0) {

printf("Bytes received: %d %s\n", iResult, recvbuf);

// Echo the buffer back to the sender

iSendResult = send( ClientSocket, recvbuf, iResult, 0 );

if (iSendResult == SOCKET_ERROR) {

printf("send failed with error: %d\n", WSAGetLastError());

closesocket(ClientSocket);

WSACleanup();

system("pause");

return 1;

}

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• Programming client/server applications in C++ is fun and

challenging.

• Client server application is basically used forcommunication from one system to another at which one

client can communicate with more then one server at a

time.

•Keywords:• Client, server, TCP/IP, port number, sockets, C# sockets

•Any Questions!!!