OSI Reference Model
The OSI Reference Model consists of 7 layers. When OSI was in active development, new protocols and specifications to implement the functions specified by each layer were made. Today, the OSI model can be used as a standard of comparison to other networking models (to TCP/IP, for example).
Let’s take a look in the OSI Reference Model layers:
7) Application.
It provides an interface between the communications software and any applications that need to communicate outside the computer on which the application resides. It also defines the authentication process.
6) Presentation.
This layer negotiates data formats, such as JPEG, binary, ASCII text, BCD and others. Encryption is defined by OSI as a presentation layer service.
5) Session.
As its name implies, this layers manages how to start, control and end conversations (called sessions).
4) Transport.
The transport layer focusses on issues related to data delivery to another host -for instance, error recovery and flow control.
3) Network.
There are three main features managed by the network layer: logical addressing, routing (forwarding) and path determination.
2) Data Link.
The protocols that determine when a device can send data over a particular medium are defined by this layer.
1) Physical.
This layer typically refers to standards from others organizations. These standars deal with the physical characteristics of the pins, use of pins, encoding, light modulations, electrical currents and the rules to activate and deactivate the use of the physical medium.
In a brief, this is the OSI Reference Model. For further explanation of this networking scheme I strongly suggest you to purchase the books shown at the right side of this page.
