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