The OSI
reference model is the primary model for network communications. The early
development of LANs, MANs, and WANs was confused in many ways. The early 1980
saw great increases in the number and sizes of networks. As companies realized
that they could save money and gain productivity by using networking
technology, they added networks and expanded existing networks as rapidly as
new network technologies and products were introduced.
In 1984, the
International Organization for Standardization (ISO) developed the OSI
Reference Model to describe how information is transferred from one networking
component to another, from the point when a user enters information using a
keyboard and mouse to when that information is converted to electrical or light
signals transferred along a piece of wire (or radio waves transferred through
the air).
ISO
developed the seven-layer model to help vendors and network administrators gain
a better understanding of how data is handled and transported between
networking devices, as well as to provide a guideline for the implementation of
new networking standards and technologies. To assist in this process, the OSI
Reference Model separates the network communication process into seven simple
layers.
Dividing the
network into seven layers provide these advantages:
Reduces complexity:
It breaks
network communication into smaller, simpler parts. It divides the network
communication process into smaller and simpler components, thus aiding
component development, design, and troubleshooting.
Standardizes interfaces:
It
standardizes network components to allow multiple vendor development and
support.
Facilitates modular engineering:
It allows
different types of network hardware and software to communicate with each other.
Interoperability between Vendors
It allows
multiple-vendor development through standardization of network components.
Defines the process for connecting two layers together, promoting
interoperability between vendors It Allows vendors to compartmentalize their
design efforts to fit a modular design, which eases implementations and
simplifies troubleshooting
Ensures interoperable technology:
It prevents
changes in one layer from affecting the other layers, allowing for quicker
development.
Accelerates evolution:
It provides
for effective updates and improvements to individual components without
affecting other components or having to rewrite the entire protocol.
Simplifies teaching and learning:
It breaks
network communication into smaller components to make learning easier. Provides
a teaching tool to help network administrators understand the communication
process used between networking components
The OSI Reference Model
- The OSI reference model
consists of seven layers: physical, data-link, network, transport,
session, presentation, and application.
- The OSI model layers usually do
not correspond exactly to the protocol stack running on an actual system.
- The data-link layer protocols
often include physical layer specifications.
- The network and transport layer
protocols work together to provide a cumulative end-to-end communication
service.
- The functions of the session,
presentation, and application layers are often combined into a single
application layer protocol.
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