• Unreliable Datagram Protocol
• Packet Oriented, not stream oriented like TCP/IP
• Much faster but no error correction
• NFS, TFTP, and FSP use UDP/IP
• Must fit data into packets of about 8K or less
  //

The UDP Classes

• Java's support for UDP is contained in two classes:
• java.net.DatagramSocket
• java.net.DatagramPacket
• A datagram socket is used to send and receive datagram packets.

java.net.DatagramSocket

• A DatagramSocket object is a local connection to a port that conducts the sending and receiving.
• DataGramPackets are not mutable
•  UDP socket and UDP server socket, are the same
• In contrast to  TCP sockets, a DatagramSocket can send to multiple, different addresses.
• The address to where the data was sent, would be stored in the packet, and  not in the socket.

• Each computer has 65,536 UDP ports as well as its 65,536 TCP ports.
• A TCP and UDP port can bind to the same port.

• public DatagramPacket(byte[] data, int length)
  
  public DatagramPacket(byte[] data, int length, InetAddress iaddr, int iport)
  
  First is for receiving, second is for sending.
  For example,
  
  String s = "Some UDP Packet"
  byte[] b = s.getBytes();
  DatagramPacket dp = new DatagramPacket(b, b.length);

try {
InetAddress intaddr = new InetAddess("intaddr.ABC.com");
int n1 = 40;
String str1 = "Another UDP Packet"
byte[] bt1 = str1.getBytes();
DatagramPacket dp = new DatagramPacket(bt1, bt1.length, intaddr, n1);
}
catch (UnknownHostException e) {
System.err.println(e);
}

• public synchronized void setAddress(InetAddress iaddr)
• public synchronized void setPort(int iport)
• public synchronized void setData(byte ibuf[])
• public synchronized void setLength(int ilength)
• public synchronized InetAddress getAddress()
• public synchronized int getPort()
• public synchronized byte[] getData()
• public synchronized int getLength()

• client datagram socket , sent prior to receiving any
  public DatagramSocket() throws SocketException
• Followed by two server datagaram sockets to specify the port and IP address of the socket
  • public DatagramSocket(int port) throws SocketException
  • public DatagramSocket(int port, InetAddress laddr) throws SocketException