THE ISO STANDARD MODEL FOR COMMUNICATIONS: OSI

 

  • ISO (the International Organization for Standardisation) has developed a standard model for communications, called the
OSI (Open Systems Interface) Model
  • Model = it means that it's only theory! In fact the OSI model is not yet fully implemented in real networks.
  • Open System : It can communicate with any other system that follows the specified standards, formats, and semantics.
  • Protocols give rules that specifiy how the communication parties may communicate.
  • Supports two general types of protocols. Both are common.
    • Connection-Oriented :
      • Sender and receiver first establish a connection, possibly negotiate on a protocol. (virtual circuit)
      • Transmit the stream of data.
      • Release the connection when done.
      • E.g. Telephone connection.
    • Connectionless
      • No advance setup is needed.
      • Transmit the message ( datagrams ) when sender is ready.
      • E.g. surface mail