SOCKET PROGRAMMING experiment, Study Guides, Projects, Research of Computer Networks

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EXPERIMENT – 8

SOCKET PROGRAMMING

Aim – To implement Socket programming in Java using UDP

Theory –

Socket

Sockets allow communication between two different processes on the same or different

machines. To be more precise, it's a way to talk to other computers using standard Unix file

descriptors.

Socket Types –

There are four types of sockets available to the users. The first two are most commonly used

and the last two are rarely used. Processes are presumed to communicate only between

sockets of the same type but there is no restriction that prevents communication between

sockets of different types.

1. Stream Sockets − Delivery in a networked environment is guaranteed. If you send

through the stream socket three items "A, B, C", they will arrive in the same order −

"A, B, C". These sockets use TCP (Transmission Control Protocol) for data

transmission. If delivery is impossible, the sender receives an error indicator. Data

records do not have any boundaries.

2. Datagram Sockets − Delivery in a networked environment is not guaranteed. They're

connectionless because you don't need to have an open connection as in Stream

Sockets – you build a packet with the destination information and send it out. They

use UDP (User Datagram Protocol).

3. Raw Sockets – These provide users access to the underlying communication

protocols, which support socket abstractions. These sockets are normally datagram

oriented, though their exact characteristics are dependent on the interface provided

by the protocol.

4. Sequenced Packet Sockets – They are similar to a stream socket, with the exception

that record boundaries are preserved. This interface is provided only as a part of the

Network Systems (NS) socket abstraction, and is very important in most serious NS

applications. Sequenced-packet sockets allow the user to manipulate the Sequence

Packet Protocol (SPP) or Internet Datagram Protocol (IDP) headers on a packet or a

group of packets, either by writing a prototype header along with whatever data is

to be sent, or by specifying a default header to be used with all outgoing data, and

allows the user to receive the headers on incoming packets.

6. Acknowledgment mechanism: -

The UDP does have any acknowledgment mechanism, i.e., there is no handshaking

between the UDP sender and UDP receiver. If the message is sent in TCP, then the

receiver acknowledges that I am ready, then the sender sends the data. In the case

of TCP, the handshaking occurs between the sender and the receiver, whereas in

UDP, there is no handshaking between the sender and the receiver.

7. Segments are handled independently: -

Each UDP segment is handled individually of others as each segment takes different

path to reach the destination. The UDP segments can be lost or delivered out of

order to reach the destination as there is no connection setup between the sender

and the receiver.

8. Stateless: -

It is a stateless protocol that means that the sender does not get the

acknowledgement for the packet which has been sent.

Java Socket programming can be connection-oriented (TCP) or connectionless (UDP). But for

this experiment we are considering Java socket programming using UDP protocol.

 Socket and ServerSocket classes are used for connection-oriented socket

programming

 DatagramSocket and DatagramPacket classes are used for connection-less socket

programming.

The client in socket programming must know two parameters –

 IP Address of Server, and

 Port number.

UDPServer Code –

import java.io.IOException; import java.net.DatagramPacket; import java.net.DatagramSocket; import java.net.InetAddress; import java.net.SocketException; public class UDPServer { public final static int SERVICE_PORT = 50001 ; public static void main(String[] args) throws IOException { try { DatagramSocket serverSocket = new DatagramSocket(SERVICE_PORT); byte[] receivingDataBuffer = new byte[ 1024 ]; byte[] sendingDataBuffer = new byte[ 1024 ]; DatagramPacket inputPacket = new DatagramPacket(receivingDataBuffer, receivingDataBuffer.length); System.out.println("Waiting for a client to connect..."); serverSocket.receive(inputPacket); String receivedData = new String(inputPacket.getData()); System.out.println("Sent from the client: " + receivedData); sendingDataBuffer = receivedData.toUpperCase().getBytes(); InetAddress senderAddress = inputPacket.getAddress(); int senderPort = inputPacket.getPort(); DatagramPacket outputPacket = new DatagramPacket(sendingDataBuffer, sendingDataBuffer.length, senderAddress, senderPort); serverSocket.send(outputPacket); serverSocket.close(); } catch (SocketException e) { e.printStackTrace(); } } }

DatagramPacket sendingPacket = new DatagramPacket(sendingDataBuffer, sendingDataBuffer.length, IPAddress, SERVICE_PORT); clientSocket.send(sendingPacket); DatagramPacket receivingPacket = new DatagramPacket(receivingDataBuffer, receivingDataBuffer.length); clientSocket.receive(receivingPacket); String receivedData = new String(receivingPacket.getData()); System.out.println("Sent from the server: " + receivedData); clientSocket.close(); } catch (SocketException e) { e.printStackTrace(); } } }

Output –

Conclusion – Thus we have studied about UDP protocol and implemented java socket

programming using UDP.