1 / 23

Java Networking UDP Yangjun Chen Dept. Business Computing University of Winnipeg

Java Networking UDP Yangjun Chen Dept. Business Computing University of Winnipeg. User Datagram Protocol. UDP (User Datagrarn Protocol) - a protocol that sends independent packets of data, called datagrams, from one computer to another with no guarantees about arrival

dylan
Télécharger la présentation

Java Networking UDP Yangjun Chen Dept. Business Computing University of Winnipeg

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Java Networking UDP Yangjun Chen Dept. Business Computing University of Winnipeg

  2. User Datagram Protocol • UDP (User Datagrarn Protocol) • - a protocol that sends independent packets of data, called datagrams, • from one computer to another with no guarantees about arrival • - not connection based like TCP • If a UDP packet is lost, IT’S LOST. • The packets appear in the order they are received not necessarily in the order they were sent.

  3. So Why UDP? • Speed! • UDP can be up to three times faster than TCP. • There are applications where speed is more important than reliability, such as audio and video data.

  4. UDP • Java classes using UDP • - java. net • DatagramPacket() • DatagramSocket()

  5. UDP Classes • Java has two classes for UDP support • java.net.DatagramSocket • java.net.DatagramPacket • A DatagramSocket is used to send and receive DatagramPacket. • Since UDP is connectionless, streams are not used. • The maximum size of a Datagrarm packet is • limited to slightly less than 64Kbytes.

  6. UDP Classes • DatagramSockets are connected to a port that allow for sending and receiving of data. • Unlike TCP sockets, there is no distinction between client and server sockets in UDP. • Also, a DatagramSocket can be used to send data to multiple different hosts. • - This is because the address is stored in the packet, not in • the socket. • There are 65,536 UDP ports as well as TCP ports that are separate from each other.

  7. DatagramPacket Class • You construct a DatagrarmPacket by using one of the two constructors. • - public DatagramPacket(byte[] data, int length) • - public DatagramPacket(byte[] data, int length, • InetAddress addr, int port) • The byte array is passed by reference and not by value. A change in its contents will change the packet.

  8. DatagramPacket Class • Example of using the constructors: • String data = "My UDP Packet”; • byte[] h = data.getBytes(); • DatagramPacket dp = new DatagramPacket(b, b.length) • You can also pass in the host and port to which the packet is to be sent.

  9. DatagramPacket Class try { InetAddress tr = new InetAddress(" www.win.trlabs.ca”); int port = 9100; String data = "Another UDP Packet"; byte[] b = data.getBytes( ); DatagramPacket dp = new DatagramPacket(b, b.length, tr,port); }//try catch (UnknownHostException e) { System.err.printin(e); }//catch

  10. DatagramPacket Class • After creation of a DatagramPacket, it is possible to change the date, the length of the data, the port, or the address by using the following methods: • setAddress(InetAddress addr) • setPort(int port) • setData(byte buf[]) • setLength(int length) • To retrieve the current status of a DatagramPacket, use the corresponding get methods.

  11. DatagramSocket Class • This class is a connection to a port that does the transmitting and receiving. • Unlike TCP sockets, the same Datagramsocket can be used to send and receive. • The Datagramsocket class has three constructors.

  12. DatagramSocket Class • public DatagramSocket() • public DatagramSocket(int port) • public Datagramsocket(int port, InetAddress addr) • all three constructors throw an IOException. • The first constructor is mainly used to act as clients. • The other two that specify a port and optionally an IP address are intended for servers that must run on a well known port.

  13. Sending UDP Datagrams • 1) Convert the data into a byte array. • 2) Pass this byte array, length of data, port and address to the DatagramPacket constructor. • 3) Create a DatagramSocket object. • 4) Pass the Datagram packet to the send method.

  14. Sending UDP Datagrams try { TnetAddress tr=new InetAddress("win.tr1abs.ca”); int pt=9100; string data = "Sending a Datagram"; byte[] b = data.getBytes(); DatagramPacket dP=new DatagramPacket(b,b.length,tr,pt); }//try catch (UnknownHostException e) { system.err.println(e); }//catch

  15. Sending UDP Datagrams try { DatagramSocket sender = new Datagramsocket(); sender.send(dP); }//try catch (IOException e) { system.out.printIn(e); }//catch

  16. Receiving UDP Datagrams • 1) Construct a DatagramSocket object on the port you wish to listen. • 2) Pass it an empty Datagrampacket object to the Datagramsocket’s receive() method. • 3) Use methods • getport ( ), • getAddress( ), • getData ( ), • getLength( ) • to retrieve information about the data.

  17. Receiving UDP Datagrams try { byte buf=new byte[655361; DatagramPacket dp = new DatagramPacket(buf, buf.length); DatagramSocket ds=newDatagramSocket(9100); ds.receive(dp); byte[] data=dp.getData(); String s=new String(data, 0, data.getLength()); System.out.println(s); }//try catch (IOException e) { System.err.println(e); }//catch

  18. UDP Echo Example • As with the TCP echo port, the UDP echo port is port 7. • When this port receives a datagram, it copies the data and sends it back to the user. • As with the TCP echo example, the UDP echo example will read in data from System.in, send it to the echo server on port 7 and then display the results. • Remember that since UDP is connectionless, a packet might be lost somewhere between the client and the server.

  19. UDP Echo Example import java.io.*; import java.net.*; public class UDPEcho extends Thread { static int port=7; static volatile boolean running=false; DatagramSocket ds; public static void main(String args[]) { InputstreamReader isr=new InputStreamReader(System.in); BufferedReader in = new BufferedReader(isr); String line;

  20. UDP Echo Example running=true; try{ while ((line==in.readLine()) != null) { byte[] data = line.getBytes(); DatagramPacket dP = new DatagramPacket (data, data.length, server, port); ds.send(dp); Thread.yield(); }//while }//try

  21. UDP Echo Example catch(IoException e) { system.err.println(e); } //catch running = false; } //main public UDPEcho(DatagramSocket ds) { this.ds=ds; } //UDPEcho constructor

  22. UDP Echo Example public void run() { byte[] buf = new byte[1024]; String line; DatagramPacket incoming = new DatagramPacket (buf, buf.length); while(running) { try{ ds.receive(incoming); byte[] data = incoming.getData(); line = new String(data,0,incoming.getLength());

  23. UDP Echo Example System.out.println("Echo: ", line); } //try catch(IOException e){ system.err.println(e); }//catch }//while }//run }//UDPEcho class

More Related