Cables to Go CDM-570L manual OSI Reference Model, Layers 1

The OSI Reference Model

The OSI Reference Model

OSI is an acronym for Open Systems Interconnection. This is a network model created by ISO (the International Standardization Organization.) The OSI model is the basic standard which forms the basis for all networking protocols.

Figure A-1The Seven OSI Protocol Layers

The OSI model defines the building blocks used to construct a working network protocol as shown in Figure A-1. The blocks on the right show the individual layers which make up the OSI model and the blocks on the left show the layer’s functional grouping.

Each layer, as defined by the OSI model, is only aware of the layers directly above and below it.

Layers 1 – 3

Layer 1 / Physical – Layer 1 defines the physical means by which actual bits are sent and received. This layer, for example, is where connectors, cable lengths, and signaling specifications are defined.

Layer 2 / Data Link – Layer 2 consist of two sub-layers:

•Logical Link Control (LLC) – The LLC packages bytes received from the MAC into a format readable by the Network Layer above it.

•Media Access Control (MAC) – The MAC is concerned with obtaining access to the network at an appropriate time; i.e., when no other machines are communicating or when permission has been granted.

Together, these two sub-layer protocols are responsible for moving packets on and off the network.

A-2 Vipersat CDM-570/570L User Guide