The OSI protocols are vendor-neutral protocols that functionally support the individual layers of the OSI reference model. In the initial phase, after the standardization of the reference model in 1983, some protocols were introduced for the transport layer, the communication control layer and the application layer. After that, new protocols and services were developed regularly, but they lack the necessary market acceptance. This is often due to the long development times, during which very often vendor developments became quasi-standards.
The physical layer is supported by the OSI protocols in all conceivable mechanisms, from simple modems to 2 Gbit/s crossconnect switches. The datalink layer protocols support all access methods, from High Level Data Link Control( HDLC), Logical Link Control( LLC), CSMA/ CD, Token Bus and Token Ring to FDDI.
The network layer provides routing and enables logically structured networks to be set up. In the OSI protocols, the network layer is divided into two parts to support connectionless and connection-oriented services. The routing protocols are End System to Intermediate System( ES-IS) and Intermediate System to Intermediate System( IS-IS). The transport layer provides a transparent connection between the end systems. The corresponding service is available in connectionless or connection-oriented form. The OSI transport protocols( OSI-TP) offer different transport classes and service qualities. There are a total of five transport classes to choose from. OSI 8073 is a connection-oriented transport protocol used in the Digital Network Architecture( DNA).
The communication control layer is split into two protocols for connectionless and connection-oriented services. OSI 8327 is a session layerprotocol used in the Digital Network Architecture (DNA). The presentation layer uses Abstract SyntaxNotation One( ASN.1) as the coding or decoding language.
Application-specific protocols are provided for the application layer. The best known of a large number are File Transfer Access and Management( FTAM), X.400, X.500, Virtual Terminal Service (VTS), Common Management Information Protocol( CMIP) and Common Management Information Service( CMIS).