MULTICAST NETWORK PROGRAMMING - Unicast is point-to-point communication. - Broadcast is communication to all connected members. - Multicast is communication to a selected set of connected members. Multicast Applications - Videoconferencing - Usenet news - Computer configuration Multicast Addresses and Groups - IP address range: 224.0.0.0 to 239.255.255.255 (i.e. first four bits is 1110) - These are the class D addresses. - A multicast group is a set of host that shares a multicast address. - To create a multicast group, select a random address from 225.0.0.0 to 238.255.255.255. After which, create an InetAddress object for that address and start sending it data. - Try pinging all-routers.mcast.net to check multicasting capability of the network. Common Permanent Multicast Addresses - 224.0.0.1 ( all-systems.mcast.net ) – all systems on the local subnet. - 224.0.0.2 ( all-routers.mcast.net ) – all routers on the local subnet. - 224.0.0.11 ( mobile-agents.mcast.net ) – mobile agents on the local subnet. - 224.0.1.1 ( ntp.mcast.net ) – the network time protocol. - 224.0.1.20 ( experiment.mcast.net ) – experiments that do not beyond the local subnet - 224.2.X.X (Multicast Backbone on the Internet (MBONE)) – used for audio and video broadcasts over the Internet. Sending Multicast Data - Communication is connectionless. Datagrams are simply UDP datagrams addressed to a multicast group. - Need to create a MulticastSocket and put the multicast address in the Datagram packet that is to be sent. - Need to set the Time-to-Live (TTL) value properly for the datagram to be received properly. TTL ( 0 – 255 ) is approximately the number of routers a frame goes through before it is discarded. - Approximate TTL values are: 0 for localhost; 1 for local subnet; 32 for high-bandwidth site in the USA; 48 for the USA; 64 for North America, 255 for worldwide.- When the datagram is sent, it is the responsibility of the multicast routers to duplicate the data and route it to the multicast group members. Java MulticastSocket Class - The MulticastSocket class is a subclass of the DatagramSocket class: Public class MulticastSocket extends DatagramSocket - Constructors: MulticastSocket ( ) throws SocketException MulticastSocket ( int portNum ) throws SocketException - Methods: public void joinGroup(inetAddress mAddr) throws IOexception used to join a multicast group using the address, mAddr. Here is an example: import java.net.*; import java.io.*; public class MulticastJoin { public static void main(String [ ] args){ try { MulticastSocket mSocket = new MulticastSocket(4001); InetAddress mAddr = InetAddress.getByName("224.0.0.1"); mSocket.joinGroup(mAddr); byte [ ] buffer = new byte[512]; while (true) { DatagramPacket dp = new DatagramPacket(buffer, buffer.length); mSocket.receive(dp); String str = new String(dp.getData(), "8859_1"); System.out.println(str); }//end of while }//end of try catch (SocketException se){ System.out.println("Socket Exception : " + se); } catch (IOException e) { System.out.println("Exception : " + e); } }//end of main }// end of class definitionpublic void leaveGroup(inetAddress mAddr) throws IOexception used to signal the router that the computer is no longer interested in receiving multicast datagrams. public void send(DatagramPacket packet, byte TTL) throws IOexception public void send(DatagramPacket packet) throws IOexception used to send the previously configured datagram packet with or without a specified time-to-live value. Here is an example: import java.net.*; import java.io.*; public class MulticastSend { public static void main( String [ ] args) { try { MulticastSocket mSocket = new MulticastSocket( ); InetAddress mAddr = InetAddress.getByName("224.0.0.1"); String hostname = InetAddress.getLocalHost().getHostName(); String sendString = "Hello from " + hostname; byte [ ] buffer = sendString.getBytes(); DatagramPacket dp = new DatagramPacket(buffer, buffer.length, mAddr, 4001); mSocket.send(dp); } catch (SocketException se) { System.out.println("Socket Exception : " + se); } catch (IOException e) { System.out.println("Exception : " + e); } }//end of main }// end of class definitionpublic void setInterface(InetAddress addr) throws SocketException used to select the network interface to be used for multicasting in a multihomed system. public InetAddress getInterface() throws SocketException used to determine the address of the interface involved in multicasting. public void setTimeToLive(int TTL) throws IOException public int getTimeToLive( ) throws IOException sets/gets the time-to-live value of the datagram packet.Here is one final example of multicasting: import java.net.*; import java.io.*; public class MulticastListener { public static void main( String [ ] args) { InetAddress mAddr=null; MulticastSocket mSocket=null; final int PORT_NUM= 4001; try { mAddr = InetAddress.getByName("audionews.mcast.net"); mSocket = new MulticastSocket(PORT_NUM); String hostname = InetAddress.getLocalHost().getHostName(); byte [ ] buffer = new byte[8192]; mSocket.joinGroup(mAddr); System.out.println("Listening from " + hostname + " at " + mAddr.getHostName()); while (true){ DatagramPacket dp = new DatagramPacket(buffer, buffer.length); mSocket.receive(dp); String str = new String(dp.getData(), "8859_1"); System.out.println(str); }//end of while } catch (SocketException se) { System.out.println("Socket Exception : " + se); } catch (IOException e) { System.out.println("Exception : " + e); } finally { if (mSocket != null){ try { mSocket.leaveGroup(mAddr); mSocket.close(); } catch (IOException e){ } }//end of if }//end of finally }//end of main