1. Network Programming in Java CS 1111 Ryan Layer May 3, 2010

2. Vocabulary Client Server Packet switched network Address DNS Ports
Sockets
Protocols

3. Echo client import java.net.Socket; public class Client {
public static void main(String[] args) throws Exception {
String host = args[0];
int port = Integer.parseInt(args[1]);
Socket socket = new Socket(host, port);
In in = new In(socket);
String reply = in.readLine();
System.out.println(reply);
in.close();
socket.close(); }

4. Hello World server import java.net.Socket;
import java.net.ServerSocket;
public class Server {
public static void main(String[] args) throws Exception {
int port = Integer.parseInt(args[0]);
ServerSocket serverSocket = new ServerSocket(port);
while (true) {
Socket clientSocket = serverSocket.accept();
Out out = new Out(clientSocket);
out.println("Hello World!");
out.close();
clientSocket.close(); }

5. Network Stack Internet Application Transport Network Link
WoW, HTTP, ftp, ...
Transport
TCP, UDP, ...
Network
IP, ...
Application
WoW, HTTP, ftp, ...
Internet
Link
device driver
Transport
TCP, UDP, ...
Network
IP, ...
Link
device driver

6. Network Stack
Internet

7. Ports app app app port port port IP Addr
Connection = (local addr, local port, remote addr, remote port)
server p o r t
port
client

8. Ports Connection = (local addr, local port, remote addr, remote port)
host 5
port b
(5, b, 1, a)
port a
host 1
(1, a, 5, b)
(1, b, 4, a)
(1, c, 4, b)
port b
port c
(4, a, 1, b)
(4, b, 1, c)
(4, b, 2, a)
(4, b, 3, a)
host 4
port a
port b
port a
host 2
(2, a, 4, b)
port a
host 3
(3, a, 4, b)

9. Putting it All Together
Sender
Receiver
msg
app
app
app
Application
src port, dst port
src port, dst port
msg
msg
Transport
src IP, dst IP
src IP, dst IP
src port, dst port
src port, dst port
msg
msg
Network
src IP, dst IP
src port, dst port
msg
src MAC, dst MAC
src IP, dst IP
src port, dst port
msg
src MAC, dst MAC
Link
Internet

10. What You Need to Remember:
Servers listen on ports
Clients connect and address and a port
Transport layer protocol (TCP, UDP) matters
Write to / read from sockets to communicate

11. Application Protocols, HTTP
telnet 80
GET /index.html
HEAD: Asks for the response identical to the one that would correspond to a GET request, but without the response body.
GET: Requests a representation of the specified resource.
POST: Submits data to be processed to the identified resource.
PUT: Uploads a representation of the specified resource.
DELETE: Deletes the specified resource.
TRACE: Echoes back the received request.
OPTIONS: Returns the HTTP methods that the server supports.
CONNECT: Converts the request connection to a transparent TCP/IP tunnel.
PATCH: Is used to apply partial modifications to a resource.

12. Vocabulary Client Server Packet switched network Address DNS Ports
Sockets
Protocols