UDP

User Datagram Protocol

About the UDP A commonly used transport protocol

Does not guarantee either packet delivery or order

The packets may travel along different paths

Each packet has a time-to-live (TTL) counter

Arrives intact or is idscarded

The advantages of UDP More efficient than guaranteed-delivery

Unlike TCP streams, which establish a connection

Real-time application that demand up-to-second or better performance may be candidates for UDP

can receive data from more than one host machine

Some network protocols specify UDP as the transport mechanism (e.g. …)

Java classes to support UDP

java.net.DatagramPacket

java.net.DatagramSocket

DatagramPacket class Packets are containers for a small seq

uence of bytes, and include addressing information such as an IP address and a port number

The DatagramPacket class repesents a data packet intended for transmission using the UDP protocol

Note: When a DatagramPacket is used to send an

UDP packet, the IP address stored in DatagramPacket represents the address of the recipient (likewise with the port number)

When a DatagramPacket has been read from a UDP socket, the IP address of the packet represents the address of the sender (likewise with the port number)

Creating a DatagramPacket

To send data to a remote machine using UDP

To receive data sent by a remote machine using UDP

Constructors For receiving incoming UDP packets:

DatagramPacket(byte[] buffer, int length) For example:

DatagramPacket packet=new DatagramPacket(new byte[256], 256);

To send a DatagramPacket to a remote machine: DatagramPacket(byte[] buffer, int length, InetAddress dest_

addr, int dest_port) For example:

InetAddress addr=InetAddress.getByName(“192.168.0.1”)DatagramPacket packet=new DatagramPacket(new byte[128], 1

28, addr, 2000);

Using a DatagramPacket Methods

InetAddress getAddress() byte[] getData() int getLength() int getPort()

void setAddress(InetAddress addr) void setData(byte[] buffer) void setLength(int length) void setPort(int port)

DatagramSocket class

Provides access to a UDP socket, which allow UDP packets to be sent and received

Creating a DatagramSocket Constructors

To create a client DatagramSocket: DatagramSocket()

To create a server DatagramSocket: DatagramSocket(int port)

Using a DatagramSocket Methods

void close()

InetAddress getInetAddress() int getPort() InetAddress getLocalAddress() int getLocalPort()

void receive(DatagramPacket packet)

Listening for UDP packetsDatagramSocket socket=new DatagramSocket(2000);DatagramPacket packet=new DatagramPacket(new byte[2

56], 256);

While (! finished){

socket.receive(packet); //read operations are blocking// process the packet

}socket.close();

Processing UDP packets

ByteArrayInputStream bin=new ByteArrayInputStream(packet.getData());

DataInputStream din=new DataInputStrteam(bin);

// Read the contents of the UDP packet……

Sending UDP packetsDatagramSocket socket=new DatagramSocket(2005);DatagramPacket packet=new DatagramPacket(new byte[25

6], 256);packet.setAddress(InetAddress.getByName(somehost));packet.setPort(2000);Boolean finished=false;While (! finished){

// write data to packet buffer……socket.send(packet);

}

Code for PacketReceiveDemo……

Code for PacketSendDemo……