User Datagram Protocol
  • 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:
  • A datagram socket is used to send and receive datagram packets.

  • 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.
// UDP ports
  • 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.
Two DatagramPacket Constructors
  • 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);
UDP -Destination:

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

Datagram Methods:
  • 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()
DatagramSocket cleint server volleys.
  • 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