User Datagram Protocol (UDP)

User Datagram Protocol (UDP) 

User Datagram Protocol (UDP) is a TCP/IP standard defined in RFC 768, "User Datagram Protocol (UDP)." UDP is used by some programs instead of TCP for fast, lightweight, unreliable transportation of data between TCP/IP hosts.

UDP provides a connectionless datagram service that offers best-effort delivery, which means that UDP does not guarantee delivery or verify sequencing for any datagrams. A source host that needs reliable communication must use either TCP or a program that provides its own sequencing and acknowledgment services.

UDP messages are encapsulated and sent within IP datagrams, as shown in the following illustration.

 

 

UDPServer.java:

import java.io.*; import java.net.*; class UDPServer {    public static void main(String args[]) throws Exception       {          DatagramSocket serverSocket = new DatagramSocket(9876);             byte[] receiveData = new byte[1024];             byte[] sendData = new byte[1024];             while(true)                {                   DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);                   serverSocket.receive(receivePacket);                   String sentence = new String( receivePacket.getData());                   System.out.println("RECEIVED: " + sentence);                   InetAddress IPAddress = receivePacket.getAddress();                   int port = receivePacket.getPort();                   String capitalizedSentence = sentence.toUpperCase();                   sendData = capitalizedSentence.getBytes();                   DatagramPacket sendPacket =                   new DatagramPacket(sendData, sendData.length, IPAddress, port);                   serverSocket.send(sendPacket);                }       } }

UDPClient.java:

import java.io.*; import java.net.*; class UDPClient {    public static void main(String args[]) throws Exception    {       BufferedReader inFromUser =       new BufferedReader(new InputStreamReader(System.in));       DatagramSocket clientSocket = new DatagramSocket();       InetAddress IPAddress = InetAddress.getByName("localhost");       byte[] sendData = new byte[1024];       byte[] receiveData = new byte[1024];       String sentence = inFromUser.readLine();       sendData = sentence.getBytes();       DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);       clientSocket.send(sendPacket);       DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);       clientSocket.receive(receivePacket);       String modifiedSentence = new String(receivePacket.getData());       System.out.println("FROM SERVER:" + modifiedSentence);       clientSocket.close();    } }       String sentence = inFromUser.readLine();       sendData = sentence.getBytes();       DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);       clientSocket.send(sendPacket);       DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);       clientSocket.receive(receivePacket);       String modifiedSentence = new String(receivePacket.getData());       System.out.println("FROM SERVER:" + modifiedSentence);       clientSocket.close();    } }