The OSI Model

prim02.gifThe Application layer is the entrance point that programs use to access the OSI model and utilize network resources. Most application layer protocols provide services that programs use to access the network.

The Presentation layer. There is only one function found at the presentation layer, and that is the translation of syntax between different systems.

Session layer functions are integrated into other protocols that include presentation and application layer functions.

The Transport and network layer protocols used to transmit data are often thought of as a matched pair. These include the TCP, which runs at the transport layer, plus the IP, which runs at the network layer.

Network layer maintains and terminates network connections allowing for the passage of data.

The Data-link layer is the conduit between the computer's networking hardware and its networking software.

The Physical layer defines the nature of the network's hardware elements, such as what medium the network uses, how the network is installed, and the nature of the signals used to transmit binary data over the network.

The figure represents two networked computers. They are running identical operating systems and applications and are using identical protocols (or rules) at all OSI layers. Working in conjunction, the applications, the OS, and the hardware implement the seven functions described in the OSI model.