OSI Overview

The International Organization for Standardization (ISO) produce a set of international standards to facilitate interconnection of computer systems. The Open Systems Interconnection (OSI) Reference Model subdivides the set into a series of layers. Windows Sockets allows an application to use OSI Transport protocols.

Examples of OSI profiles that may be implemented are:

• TP4/CLNS - Transport class 4 over Connectionless-mode Network Service
• TP4/NULL - Transport class 4 over Null Network Service
• TP0/CONS - Transport class 0 over Connection-mode Network Service
• NULL/CONS - Null Transport over Connection-mode Network Service
• TP0/TCP - Transport class 0 over TCP/IP (RFC1006)

The OSI profile is designated either by the protocol parameter or the lpProtocolInfo parameter to the WSASocket API. The TP4/NULL profile is a subset of the TP4/CLNS profile, and is selected by the addressing information. The default OSI profile is TP4/CLNS.

An application must use the WSAPROTOCOL_INFO structure returned by WSAEnumProtocols to discover the services provided by a particular OSI profile. For example not all OSI profiles support Connect and disconnect data.