UDP vs TCP

1. UDP vs TCP • UDP • Low-level, connectionless • No reliability guarantee • TCP • Connection-oriented • Not as efficient as UDP

2. Datagram Sockets • The sending/receiving point- Class DatagramSocket • void close() : close a datagram socket • int getLocalPort() : returns the port number on which socket is bound • InetAddress getLocalAddress() : returns the local address to which the socket is bound • void receive(DatagramPacket p) : blocks until a datagram is received and the packet’s buffer contains the data received • void send(DatagramPacket p) : sends a datagram packet from this socket

3. //Datagram Server publicclass DatagramServer { publicstaticvoid main(String[] args) { DatagramPacket datapacket, returnpacket; int port = 2018; int len = 1024; try { DatagramSocket datasocket = new DatagramSocket(port); byte[] buf = newbyte[len]; datapacket = new DatagramPacket(buf, buf.length); while (true) { try { datasocket.receive(datapacket); returnpacket = new DatagramPacket( datapacket.getData(), datapacket.getLength(), datapacket.getAddress(), datapacket.getPort()); datasocket.send(returnpacket); } catch (IOException e) { System.err.println(e); } } } catch (SocketException se) { System.err.println(se); } } }

4. //Datagram Client publicclass DatagramClient { publicstaticvoid main(String[] args) { String hostname; int port = 2018; int len = 1024; DatagramPacket sPacket, rPacket; InetAddress ia = InetAddress.getByName(hostname); DatagramSocket datasocket = new DatagramSocket(); BufferedReader stdinp = new BufferedReader( new InputStreamReader(System.in)); while (true) { String echoline = stdinp.readLine(); if (echoline.equals("done")) break; byte[] buffer = newbyte[echoline.length()]; buffer = echoline.getBytes(); sPacket = new DatagramPacket(buffer, buffer.length, ia, port); datasocket.send(sPacket); byte[] rbuffer = newbyte[len]; rPacket = new DatagramPacket(rbuffer, rbuffer.length); datasocket.receive(rPacket); String retstring = new String(rPacket.getData()); System.out.println(retstring); } catch (IOException e) { System.err.println(e); } } // while } } // end main

5. TCP Sockets • A connection is set up between the sender and the receiver • Class Socket • Socket(String host, int port) : creates a stream socket and connects it to the specified port number on the host • InputStream getInputStream() : returns an input stream for reading bytes from this socket • OutputStream getOutputStream() : returns an output stream for writing bytes to this socket

6. Server Sockets • Creates a server side socket on the specified port • class ServerSocket • InetAddress getInetAddress() : returns the address to which this socket is connected • Socket accept() : blocking method which waits for a connection to be made and accepts it

7. Example: NameServer • Maps a name to the host and port number • Create a server socket • Listen for incoming connections (accept())

8. //NameServer publicclass NameServer { NameTable table; public NameServer() { table = new NameTable(); } void handleclient(Socket theClient) { BufferedReader din = new BufferedReader (new InputStreamReader(theClient.getInputStream())); PrintWriter pout = new PrintWriter(theClient.getOutputStream()); String getline = din.readLine(); StringTokenizer st = new StringTokenizer(getline); String tag = st.nextToken(); if (tag.equals("search")) { ... } elseif (tag.equals("insert")) { ... } } publicstaticvoid main(String[] args) { NameServer ns = new NameServer(); System.out.println("NameServer started:"); ServerSocket listener = new ServerSocket(Symbols.ServerPort); while (true) { Socket aClient = listener.accept(); ns.handleclient(aClient); aClient.close(); } } }

9. //Client for name server publicclass Name { BufferedReader din; PrintStream pout; publicvoid getSocket() throws IOException { Socket server = new Socket(Symbols.nameServer, Symbols.ServerPort); din = new BufferedReader(new InputStreamReader(server.getInputStream())); pout = new PrintStream(server.getOutputStream()); } publicint insertName(String name, String hname, int portnum){ getSocket(); pout.println("insert " + name + " " + hname + " " + portnum); pout.flush(); return Integer.parseInt(din.readLine()); } public PortAddr searchName(String name) throws IOException { getSocket(); pout.println("search " + name); pout.flush(); String result = din.readLine(); StringTokenizer st = new StringTokenizer(result); int portnum = Integer.parseInt(st.nextToken()); String hname = st.nextToken(); returnnew PortAddr(hname, portnum); } publicstaticvoid main(String[] args) { Name myClient = new Name(); myClient.insertName("hello1", "birch.ece.utexas.edu", 1000); PortAddr pa = myClient.searchName("hello1"); System.out.println(pa.gethostname() + ":" + pa.getportnum()); } }

10. Remote Objects • Methods can be called by another JVM on a different host • Interface is remote if it extends Remote • Remote object implements a remote interface and extends UnicastRemoteObject publicinterface NameService extends Remote { publicint search(String s) throws RemoteException; publicint insert(String s, String hostName, int portNumber) throws RemoteException; publicint getPort(int index) throws RemoteException; public String getHostName(int index) throws RemoteException; }

11. // A name service implementation publicclass NameServiceImpl extends UnicastRemoteObject implements NameService { . . . public NameServiceImpl() throws RemoteException { } publicint search(String s) throws RemoteException { . . . } publicint insert(String s, String hostName, int portNumber) throws RemoteException { . . . } publicint getPort(int index) throws RemoteException { return ports[index]; } public String getHostName(int index) throws RemoteException { return hosts[index]; } publicstaticvoid main(String args[]) { // create security manager System.setSecurityManager(new RMISecurityManager()); NameServiceImpl obj = new NameServiceImpl(); Naming.rebind("MyNameServer", obj); System.out.println("MyNameServer bound in registry"); } }

12. Parameter Passing • Primitive types are passed by value • Objects (that are not remote) • They are serialized and then passed by value. • At the other end the objects are deserialized • Any references inside the object are also serialized • Remote Objects • Passed as remote references (stubs)

13. RMI Client • Obtain a reference for the remote object • URL for the remote object is specified as • rmi://host:port/name

14. //A RMI client program import java.rmi.*; publicclass NameRmiClient { publicstaticvoid main(String args[]) { try { NameService r = (NameService) Naming.lookup("rmi://linux02/MyNameServer"); int i = r.insert("p1", "tick.ece", 2058); int j = r.search("p1"); if (j != -1) System.out.println(r.getHostName(j) + ":" + r.getPort(j)); } catch (Exception e) { System.out.println(e); } } }