OSI Reference Model
This lesson covers the OSI reference model. It is sometimes
also called ISO or 7 layer reference model. The model was
developed by the International Standards Organization in the
early 1980's. It describes the principles for interconnection
of computer systems in an Open System Interconnection environment.
- The Layered Model
- Need of Layered Network Model
- Layer Functions
- Peer to Peer
- Layers 1 &
2: Physical & Data Link Layers
- Network Layer
- Operations of Network
- Static and Dynamic Routes
- LAN-to-LAN Routing
- Transport Layer
- Session, Presentation,
and Application Layers
The Layered Model
The concept of layered communication is essential to ensuring
interoperability of all the pieces of a network. To introduce
the process of layered communication, let’s take a look
at a simple example.
In this image, the goal is to get a message
from Location A to Location B. The sender doesn’t know
what language the receiver speaks – so the sender passes
the message on to a translator.
The translator, while not concerned with the content of the
message, will translate it into a language that may be globally
understood by most, if not all translators – thus it
doesn’t matter what language the final recipient speaks.
In this example, the language is Dutch. The translator also
indicates what the language type is, and then passes the message
to an administrative assistant.
The administrative assistant, while not concerned with the
language, or the message, will work to ensure the reliable
delivery of the message to the destination. In this example,
she will attach the fax number, and then fax the document
to the destination – Location B.
The document is received by an administrative
assistant at Location B. The assistant at Location B may even
call the assistant at Location A to let her know the fax was
The assistant at Location B will then pass the message to
the translator at her office. The translator will see that
the message is in Dutch. The translator, knowing that the
person to whom the message is addressed only speaks French,
will translate the message so the recipient can properly read
the message. This completes the process of moving information
from one location to another.
Upon closer study of the process employed
to communicate, you will notice that communication took place
at different layers. At layer 1, the administrative assistants
communicated with each other. At layer 2, the translators
communicated with each other. And, at layer 3 the sender was
able to communicate with the recipient.