1. TCP/IP Protocol Stack IP Device Drivers TCPUDP Application Sockets (Gate to network) TCP: –Establish connection –Maintain connection during the communication –Release connection –Reliable (Acknowledged, in order) UDP: –No need to setup a link –Independent packets –Not reliable (no acknowledgement)

2. Programming with Sockets Sockets are Berkeley software distribution UNIX interface to network protocols Endpoint of communication, has a type and one associated process Uses file system model (open-close-read-write) Internet vs. Unix domain

3. Client-Server Architecture request response Process request client Host: www.vcu.edu Port: 80

4. 4 steps in programming a client Open a socket. Open an input and output stream to the socket. Read from and write to the socket according to the server's protocol. Clean up.

5. Socket in Java Two important classes –Socket: a normal socket as communication end –ServerSocket: accept the incoming request ServerSocket is an analogy to the custom service phone number, it will dispatch your call to a specialized staff--- normal Socket.

6. Client Socket Creation the machine you are trying to open a connection to SOCKET DESCRIPTOR Socket MyClient; MyClient = new Socket("Machine name", PortNumber); port (a number) on which the server you want port numbers between 0 and 1,023 are reserved for for standard services, such as email, FTP, and HTTP. for your server, select one that is greater than 1,023

7. Create Server Socket If you are programming a server, then this is how you open a socket: ServerSocket MyService; try { MyServerice = new ServerSocket(PortNumber); } catch (IOException e) { System.out.println(e); }

8. Use ServerSocket: listen, accept, and Create connections from clients. Socket clientSocket = null; try { serviceSocket = MyService.accept(); } catch (IOException e) { System.out.println(e); } A blocking call, will return when a request arrive

9. Send Data to Socket at Client PrintStream output; try { output = new PrintStream(MyClient.getOutputStream()); … String inL=“hello”; output.writeBytes(inL+"\n"); }

10. Read data from Socket at Client DataInputStream input; try { input = new DataInputStream(MyClient.getInputStream()); ….. String responseLine = input.readLine(); System.out.println("Server: " + responseLine); }

11. Send Data to Socket at Server PrintStream output; try { output = new PrintStream(serviceSocket.getOutputStream()); output.println(“this is server reply”); } Use the serviceSocket: returned from the accept() call.

12. Read Data From Socket at Server Same as client case DataInputStream input; try { input = new DataInputStream(serviceSocket.getInputStream()) ; String req=input.readLine(); }

13. Close Socket Connection On the client side: try { output.close(); input.close(); MyClient.close(); } catch (IOException e) { System.out.println(e) ; } On the server side: try { output.close(); input.close(); serviceSocket.close(); MyService.close(); } catch (IOException e) { System.out.println(e); }

14. A Simple Echo Server import java.io.*; import java.net.*; public class echo3 { public static void main(String args[]) { ServerSocket echoServer = null; String line; DataInputStream is; PrintStream os; Socket clientSocket = null; try { echoServer = new ServerSocket(9999); } catch (IOException e) { System.out.println(e); } // listen and accept connections. // Open input and output streams try { clientSocket = echoServer.accept(); is = newDataInputStream (clientSocket.getInputStream()); os = new PrintStream (clientSocket.getOutputStream()); // As long as we receive data, echo that data back to the client. while (true) { line = is.readLine(); os.println(line); } } catch (IOException e) { System.out.println(e); } } }

15. A simple client smtpSocket = new Socket("128.172.167.167", 9998); os = new DataOutputStream(smtpSocket.getOu tputStream()); is = new DataInputStream(smtpSocket.getInpu tStream()); while (true){ inL=d.readLine(); os.writeBytes(inL+"\n"); if (inL.compareTo("quit")==0) break; // keep on reading from/to the socket till we receive the "Ok" from SMTP, // once we received that then we want to break. responseLine = is.readLine(); System.out.println("Server: " + responseLine); responseLine = is.readLine(); System.out.println("Server: " + responseLine); responseLine = is.readLine(); System.out.println("Server: " + responseLine); }

16. Reference Class ServerSocke –A server socket waits for requests to come in over the network. It performs some operation based on that request, and then possibly returns a result to the requester. –accept() Listens for a connection to be made to this socket and accepts it. –getInetAddress() Returns the local address of this server socket.

17. Class Socket This class implements client sockets (also called just "sockets"). A socket is an endpoint for communication between two machines. Socket(InetAddress address, int port) connect(SocketAddress endpoint) Connects this socket to the server. getPort() Returns the remote port to which this socket is connected. getLocalPort() Returns the local port to which this socket is bound.getLocalPort getInputStream() Returns an input stream for this socket.getInputStream getOutputStream() Returns an output stream for this socket.getOutputStream getInetAddress() Returns the address to which the socket is connected.getInetAddress getLocalAddress() Gets the local address to which the socket is bound.getLocalAddress

18. Other Parameters in Socket Buffer size –Incoming buffer size –Outgoing buffer size Time out or not –Otherwise a bad read will block your browser for ever. Status check