Sockets

1
Sockets

• What are Sockets?
• Why are Sockets used?
• What do Sockets do?
• How to use Sockets

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What are sockets?

• History
• Sockets were introduced in 1981 as a generic
  interface that would provide Unix to Unix
  communications over networks
• Nowadays Sockets are supported on nearly every
  operating system e.g. WindowsJavaOS
• Microsoft Windows socket is known as WinSock
• Sockets are important to know about as they
  currently (1999) are the standard for network
  application providers on TCP/IP networks

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What are sockets?

• Sockets is a method for communication between a
  client program and a server program in a network.
• Sockets is a particular convention for connecting
  with and exchanging data between two program
  processes within the same computer or across a
  network.
• A socket is defined as "the endpoint in a
  connection." Sockets are created and used with a
  set of programming requests or "function calls"
  sometimes called the sockets application
  programming interface (API)

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What are sockets?

• A socket is a way of transferring data
• The socket looks like a I/O file to your code
• There are two forms of sockets
• Client
• Server
• see photocopy of structure diagram for Server and
  Client

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Types of socket

• Stream
• Datagram
• Raw
• Stream and Datagram sockets interface to the TCP
  and User Datagram Protocol(UDP) protocols
• UDP is an alternative to the Transmission Control
  Protocol (TCP)
• Raw sockets interface to the Internet Protocol(IP)

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Vendors of sockets

• Trumpet Winsock
• Chameleon Sampler
• NetCruiser
• All the most popular sockets are in Windows 95
  onwards

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Client Socket

• There are four main operations
• Connect to a remote Machine
• Send Data
• Receive Data
• Close the connection

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Server Socket

• There are six main functions
• A socket on a separate port
• Will listen for action
• Input or Output Streams
• Will interact with Client
• One or the other can close connection
• Return to listening

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Why are sockets used?

• For simplicity
• Easier access to the network
• To set a type of protocol
• More structure in programming

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What do sockets do?

• Create a way of data transfer
• Give the programmer great power
• Provide flexibility

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How to use sockets

• Set up Server Socket
• Set up Client Socket
• Once connection established
• Create packet to send
• Send the packet

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How to use sockets

• For the Server
• Establish connection
• Listen for packet
• Send information
• Both Client and Server listen

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How to use sockets

• Depending on programming
• The Client will listen
• The Server will listen
• But the Client listens when told to
• The server should listen automatically

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Java Sockets

• Within the Java Libraries
• Networking Class - import java.net.
• Data type Socket
• import java.io.
• import java.net.
• public class SimpleServer
• public final static int PORT 6776
• protected ServerSocket listenSocket

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Exceptions

• When sending or receiving
• Try
• ServerSocket theServer new ServerSocket(444)
• while(true)
• Socket theConnection theServer.accept()
• //blocks thread until accepted
• PrintStream p new PrintStream(theConnection.ge
  tOutputStream() )
• p.println(Welcome to my server, see you
  later)
• theConnection.close()
• catch(IOException e)
• System.err.println(e)

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Client Server

• Connect to a remote machine
• Socket remoteComputer
• try
• remoteComputer Socket(helix.nih.gov, 13)
• // Ask for a socket to helix system time
• catch(IOException e)

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Streaming sockets

• Server Client
• Create a server socket
• s new ServerSocket(5432)
• Wait for a connection Open a connection
• Socket conn s.accept() Socket soc new
  Socket(Manual, 5432)
• Get an output Stream Get input Stream
• Write data onto Stream Read data from input
  Stream
• Close stream and socket Stream.close()
  soc.close()
• Close output Stream,
• connection and server sockets

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Java Sockets

• Demonstration now follows
• This is a demo of two program processes within
  the same computer

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Winsock

• Winsock (Windows sockets)
• Winsock is a programming interface and the
  supporting program that handles input/output
  requests for Internet applications in a Windows
  operating system.
• It's called Winsock because it's an adaptation
  for Windows of the Berkeley UNIX sockets
  interface.

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How Winsock work?

• WinSock is a .DLL (Dynamic Link Library) and runs
  under Windows 3.x, Windows for Workgroups,
  Windows NT, and Windows 95. The WINSOCK.DLL is
  the interface to TCP/IP and, from there, on out
  to the Internet. (TCP/IP stands for "Transmission
  Control Protocol / Internet Protocol," the
  "language" that computers on the Internet use to
  communicate with each other.)

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Winsock

• Winsock runs between an application program such
  as a Netscape browser and the Internet program in
  your computer, TCP/IP.
• A request flows in the following order
• Netscape or other application
• winsock.dll
• TCP/IP
• Modem or network card
• The Internet and
  destination

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Winsock

• Winsock provides this interface for different
  versions of the Windows operating system. A
  comparable interface exists for Mac computers.
  Beginning with Windows 95, Winsock came as part
  of the operating system, but in earlier systems,
  a Winsock program had to be installed. UNIX
  systems do not require a Winsock equivalent
  because TCP/IP and its use of sockets was
  designed to run directly with UNIX application
  programs.

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Winsock 2

• Winsock 2 is a 32-bit version of Winsock.
• In addition to TCP/IP, it provides an interface
  to a variety of protocols, including Novells
  Internetwork Packet Exchange (IPX)/Sequenced
  Packet Exchange(SPX), Integrated Services Digital
  Network(ISDN), wireless protocols, and Open
  Systems Interconnection (OSI) standard.
• Winsock 2 is included in the latest versions fo
  the Windows operating systems.

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Winsock 2

• Netscape or other application
• ws2-32.dll
  (Winsock 2)
• TCP/IP (or certain other
  protocols)
• Modem or
  network card
• The Internet and
  destination

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Winsock references

• http//home.sol.no/hen/wsock.htm
• http//www.faqs.org/faqs/windows/winsock-faq/