The
need for worldwide standardization of technologies led to the
creation of the International Organization for Standardization
(ISO). ISO is responsible for standardizing the methods by which
computers communicate worldwide. To do so, ISO created a model for
network communication, called the Open Systems Interconnection (OSI)
reference model, or the OSI model.
OSI
Model
The
OSI model divides network communications into seven layers. Each
layer carries out specific functions in transmitting data on the
network. Before data is moved through the layers of the OSI model,
it must be divided
into
packets.
A packet is a unit of information that is transmitted as a whole
from one computer to another on a network. The network passes a
packet from layer to layer, and at each layer some additional
formatting is added to the packet.
The
layer at which a protocol works describes the function of the
protocol. Some protocols work only at particular layers of the OSI
model.
|
OSI layer
|
Function
|
|
Application Layer |
Defines how applications interact with each other
|
|
Presentation Layer |
Adds common formatting for data representation |
|
Session Layer |
Establishes and maintains communications channels
|
|
Transport Layer |
Ensures error-free delivery of data |
|
Network Layer |
Addresses messages both within and between networks
|
|
Data Link Layer |
Defines access methods for the physical medium, such as the
network cable |
|
Physical Layer |
Puts the data on the physical medium |
