TCP/IP Protocol Stack

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TCP/IP Protocol Stack
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)
Application
Sockets
(Gate to network)
TCP
UDP
IP
Device Drivers
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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

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Client-Server Architecture
request
Process request
client
response
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.

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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.

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Client Socket Creation
Socket MyClientMyClient new Socket("Machine
name", PortNumber)
SOCKET DESCRIPTOR
port (a number) on which the server you want
the machine you are trying to open a connection
to
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
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Create Server Socket

• If you are programming a server, then this is how
  you open a socket
• ServerSocket MyServicetry    MyServerice
  new ServerSocket(PortNumber)                ca
  tch (IOException e)           
  System.out.println(e)        

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Use ServerSocket listen, accept, and Create
connections from clients.

• Socket clientSocket nulltry   
  serviceSocket MyService.accept()        catc
  h (IOException e)    System.out.println(e)

A blocking call, will return when a request arrive
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Send Data to Socket at Client

• PrintStream outputtry    output new
  PrintStream(MyClient.getOutputStream())
• String inLhello
• output.writeBytes(inL"\n")

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Read data from Socket at Client

• DataInputStream inputtry    input new
  DataInputStream(MyClient.getInputStream())
• ..
• String responseLine input.readLine()
• System.out.println("Server "
  responseLine)

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Send Data to Socket at Server

• Use the serviceSocket returned from the accept()
  call.

• PrintStream outputtry    output new
  PrintStream(serviceSocket.getOutputStream())outp
  ut.println(this is server reply)

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Read Data From Socket at Server

• Same as client case
• DataInputStream inputtry       input new
  DataInputStream(serviceSocket.getInputStream())
• String reqinput.readLine()

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Close Socket Connection

• On the server side
• try    output.close()   input.close()  
  serviceSocket.close()    MyService.close()
  catch (IOException e)    System.out.println(e)
  

• On the client side
• try         output.close()       
  input.close()    MyClient.close() catch
  (IOException e)    System.out.println(e)

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A Simple Echo Server

• // listen and accept connections.// Open input
  and output streamstry            clientSocket
  echoServer.accept()           is
  new DataInputStream (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)            

• 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)          

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A simple client

• smtpSocket new Socket("128.172.167.167", 9998)
• os new DataOutputStream(smtpSocket.getOutputStr
  eam())
• is new DataInputStream(smtpSocket.getInputStrea
  m())
• while (true)
• inLd.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)

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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.

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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.
• getInputStream()           Returns an input
  stream for this socket.
• getOutputStream()           Returns an output
  stream for this socket.
• getInetAddress()           Returns the address
  to which the socket is connected.
• getLocalAddress()           Gets the local
  address to which the socket is bound.

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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