OSI Model
Short for Open System Interconnection, an ISO standard
for worldwide communications that defines a networking framework for implementing
protocols in seven layers. Control is passed from one layer to the next, starting
at the application layer in one station, proceeding to the bottom layer, over
the channel to the next station and back up the hierarchy.
At one time, most vendors agreed to support OSI in one form or another, but OSI was too loosely defined and proprietary standards were too entrenched. Except for the OSI-compliant X.400 and X.500 e-mail and directory standards, which are widely used, what was once thought to become the universal communications standard now serves as the teaching model for all other protocols.
Most of the functionality in the OSI model exists in all communications systems, although two or three OSI layers may be incorporated into one.
OSI is also referred to as the OSI Reference Model or just the OSI Model.
|
Layer
|
Name
|
Function
|
|
7
|
Application Layer | Program-to-program communication |
|
6
|
Presentation Layer | Manages data representation conversions. For example, the Presentation Layer would be responsible for converting from EBCDIC to ASCII. |
|
5
|
Session Layer | Responsible for establishing and maintaining communications channels. In practice, this layer is often combined with the Transport Layer. |
|
4
|
Transport Layer | Responsible for end-to-end integrity of data transmission. |
|
3
|
Network layer | Routes data from one node to another. |
|
2
|
Data Link Layer | Responsible for physical passing data from one node to another |
|
1
|
Physical Layer | Manages putting data into the network media and taking the data off. |
For further information about the OSI Model, look at the following links:
Protocol Stacks in Relation to the OSI Model