====== Game Networking ======

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===== Networking Basics =====

  * Networking: shifting bits from point A to point B

  * Internet Protocol (IP) - Network layer
    * The [[http://en.wikipedia.org/wiki/OSI_model|Open Systems Interconnection model (OSI model)]] defines 7 abstraction "layers" for a communications system.
    * Puts data bits into a network packet that tells where the packets need to go
    * Not reliable by itself

  * User Datagram Protocol (UDP) - Transport layer
    * Uses IP for addressing and routing
    * Divides the bits of a packet into groups and sends them in several successive packets

  * Transmission Control Protocol (TCP) - Transport layer
    * Guarantees reliable delivery in the order in which the packets were sent
    * Uses IP for addressing and routing; hence better known as TCP/IP

  * Socket - An endpoint in the IP protocol for sending and receiving data between networked computers

  * Packet - A block of data sent over the network
    * transmits the identities of the sending and receiving stations, error-control information, and a payload (data or messages)

{{ http://www.cisco.com/web/about/security/images/csc_child_pages/white_papers/ip_packet.jpg }}

  * Port - Where information goes into or out of a networked computer
    * Ports for major networked services are standardized.
      * HTTP is port 80, MySQL is port 3306, SSH is port 22, etc.
      * See http://www.iana.org/assignments/port-numbers for list of port numbers

===== Network Design (Topologies) =====

  * Most common: client-server

{{ http://i.msdn.microsoft.com/Bb153244.client-server(en-us,VS.85).gif }}

  * Other designs:
    * Which one of these comes closest to a P2P (peer-to-peer) model?

{{ http://whatis.techtarget.com/WhatIs/images/topology.gif }}

===== Networking in Java =====

  * Package: java.net.*
    * You will almost certainly need the package java.io.* for Java networking
    * Useful packages:
      * [[http://docs.oracle.com/javase/1.5.0/docs/api/java/net/Socket.html|Socket]]
      * [[http://docs.oracle.com/javase/1.5.0/docs/api/java/net/ServerSocket.html|ServerSocket]]
  * Implementing a client: see [[http://rockhopper.monmouth.edu/~jchung/cs498gd/fa09/examples/SocketTest.java|SocketTest.java]]
  * Implementing a server: see [[http://rockhopper.monmouth.edu/~jchung/cs498gd/fa09/examples/SingleEchoServer.java|SingleEchoServer.java]]

==== A Simple Networked Game Example ====

  * Download [[http://rockhopper.monmouth.edu/~jchung/cs498gd/fa11/labs/NetworkedGame.zip|NetworkedGame.zip]]
    * //SimpleGameServer.java// is a standalone server meant to be compiled and run separately.
    * //PlayerClient.java// is currently set to connect to //HOST=10.1.13.147 (cslin13.monmouth.edu)//.
      * If you run //SimpleGameServer// on a computer other than cslin13, you'll need to change what HOST is set to in //PlayerClient.java//.

=== A Game Server ====

  * Manage multiple players
  * Have some capacity
    * routine must exist to determine whether server is full
  * Add and remove players
  * Send data to one or multiple players
  * Process players' inputs

=== A Game Client ===

  * Connect to game server
  * Read and process data from server
  * Send data to server (for it to process)
  * Render the content

===== Diagnostic Tools =====

  * Netcat - The network "Swiss-army knife;" reads and writes data across TCP or UDP network connections
  * [[http://www.wireshark.org/|Wireshark]] - For sniffing and analyzing packets
  * [[http://www.nmap.org/|nmap]] - Network mapper; determines open ports and server software installed on a machine

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