Multiplexing/Demux

1
Multiplexing/Demux
2
Multiplexing/demultiplexing
delivering received segments to correct socket
gathering data from multiple sockets, enveloping
data with header (later used for demultiplexing)
process
socket
application
P4
application
application
P1
P2
P3
P1
transport
transport
transport
network
network
network
link
link
link
physical
physical
physical
host 3
host 2
host 1
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How demultiplexing works

• host receives IP datagrams
• each datagram has source IP address, destination
  IP address
• each datagram carries 1 transport-layer segment
• each segment has source, destination port number
• host uses IP addresses port numbers to direct
  segment to appropriate socket

32 bits
source port
dest port
other header fields
application data (message)
TCP/UDP segment format
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Connectionless demultiplexing

• When host receives UDP segment
• checks destination port number in segment
• directs UDP segment to socket with that port
  number
• IP datagrams with different source IP addresses
  and/or source port numbers directed to same socket

• Create sockets with port numbers
• DatagramSocket mySocket1 new DatagramSocket(1253
  4)
• DatagramSocket mySocket2 new DatagramSocket(1253
  5)
• UDP socket identified by two-tuple
• (dest IP address, dest port number)

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Connectionless demux (cont)

• DatagramSocket serverSocket new
  DatagramSocket(6428)

SP provides return address
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Connection-oriented demux

• TCP socket identified by 4-tuple
• source IP address
• source port number
• dest IP address
• dest port number
• recv host uses all four values to direct segment
  to appropriate socket

• Server host may support many simultaneous TCP
  sockets
• each socket identified by its own 4-tuple
• Web servers have different sockets for each
  connecting client
• non-persistent HTTP will have different socket
  for each request

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Connection-oriented demux (cont)
S-IP B
D-IPC
SP 9157
Client IPB
DP 80
server IP C
S-IP A
S-IP B
D-IPC
D-IPC
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Connection-oriented demux Threaded Web Server
P4
S-IP B
D-IPC
SP 9157
Client IPB
DP 80
server IP C
S-IP A
S-IP B
D-IPC
D-IPC
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Java Threads
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Introduction

• TCP echo server shown in earlier tutorial handles
  one client at a time.
• This server is known as iterative server.
• Iterative servers handle clients sequentially,
  finishing with one client before servicing the
  next.
• Java threads Helps servers handle many client
  simultaneously.

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Threading Mechanisms

• Create a class that extends the Thread class
• Create a class that implements the Runnable
  interface

Thread
Runnable
Thread
MyThread
MyClass
(objects are threads)
(objects with run() body)
a
b
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1st method Extending Thread class

• Create a class by extending Thread class and
  override run() method
• class MyThread extends Thread
• public void run()
• // thread body of execution
• Create a thread
• MyThread thr1 new MyThread()
• Start Execution of threads
• thr1.start()
• Create and Execute
• new MyThread().start()

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Template

• class MyThread extends Thread
• public void run()
• System.out.println(" this thread
  is running ... ")
• class ThreadEx1
• public static void main(String args )
  
• MyThread t new MyThread()
• t.start()

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2nd method Threads by implementing Runnable
interface

• Create a class that implements the interface
  Runnable and override run() method
• class MyThread implements Runnable
• .....
• public void run()
• // thread body of execution
• Creating Object
• MyThread myObject new MyThread()
• Creating Thread Object
• Thread thr1 new Thread( myObject )
• Start Execution
• thr1.start()

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Template

• class MyThread implements Runnable
• public void run()
• System.out.println(" this thread
  is running ... ")
• class ThreadEx2
• public static void main(String args )
  
• Thread t new Thread(new
  MyThread())
• t.start()

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Example of Java Threads
ThreadExample implements Runnable interface it
can be passed to the constructor of Thread

• public class ThreadExample implements Runnable
• private String greeting
• public ThreadExample(String greeting)
• this.greeting greeting
• public void run( )
• while(true)
• System.out.println(Thread.currentThread(
  ).getName( ) " "greeting)
• try
• TimeUnit.MILLISECONDS.sleep(((long)
  Math.random( ) 100))
• catch(InterruptedException e)
• public static void main(String args)
• new Thread(new ThreadExample(Greeting
  1")).start( )
• new Thread(new ThreadExample(Greeting
  2")).start( )
• new Thread(new ThreadExample(Greeting
  3")).start( )

Each instance of ThreadExample contains own
greeting string
Returns reference to current thread
Returns name of thread as string
Suspend the thread Thread sleeps for random
amount of time.

1. Create new instance of ThreadExample with
   different greeting
2. Passes new instance to the constructor of Thread.
3. Calls new Thread instance's start()

Each thread independently executes run() of
ThreadExample, while the main thread terminates.
Upon execution an interleaving of three greeting
messages is printed
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Multithreaded Java Server

• import java.io.
• import java.net.
• public class MultiThreadServer implements
  Runnable
• Socket csocket
• MultiThreadServer(Socket csocket)
• this.csocket csocket
• public static void main(String args) throws
  Exception
• ServerSocket ssock new ServerSocket(1234)
• System.out.println("Listening")
• while (true)
• Socket sock ssock.accept()
• System.out.println("Connected")
• new Thread(new MultiThreadServer(sock)).star
  t()

• public void run()
• try
• PrintStream pstream new
  PrintStream(csocket.getOutputStream())
• for (int i 100 i gt 0 i--)
• pstream.println(i " counts")
• pstream.close()
• csocket.close()
• catch (IOException e)
• System.out.println(e)