The OSI Reference Model
A-2 Vipersat CDM-570/570L User Guide
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-1
The Seven OSI Protocol Layers
The OSI model defines the building blocks used to construct a working network
protocol as shown in FigureA-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.