Computer Network
Models : Introduction
- For data
communication to take place and two or more users can transmit data from one
to other, a systematic approach is required. This approach enables users to
communicate and transmit data through efficient and ordered path. It is
implemented using models in computer networks and are known as computer
network models.
- Computer network
models are responsible for establishing a connection
among the sender and receiver and transmitting the data in a smooth manner
respectively.
- There are two
computer network models i.e. OSI Model
and TCP/IP Model on which the whole
data communication process relies.
Computer Network Models
Computer Network
Models : The OSI Reference
Model
- The OSI Model is one
of the general purpose networking or communication model among computer
network models, which is responsible for establishing connection in an open
manner between all the communicable devices present across the
globe.
- OSI stands for
“Open System Interconnection” and the
name of this reference model was given by an organization known as “International Organization for
Standardization”. The ISO is responsible for generating and
promoting industrial and commercial standards applicable for all the users
or universally.
- OSI model is called
as “Open Source” because of its “fit anywhere” ability. Any connection can
be established using the OSI model unless and until any protocols are not
used as OSI model does not support protocol establishment. It runs without
the use of protocols. All the networking devices which are open for
communication can be connected together for data communication through the
OSI model.
- Apart from OSI Model, another computer network models which is widely used is TCP/IP
Model.
- OSI model having a
layered architecture, allows easy data communication as each layer has
predefined structured and functionalities.
- The functionalities
are different for each layer and thus when combined together forms the OSI
Model. There are in total seven layers in general purpose OSI
model.
- The seven layers of OSI model are further categorized into Upper
Layers, Network Independent
Layer and Lower Layers.
Physical Layer, Data link Layer and Network Layer are categorized as Lower
Layers. Transport Layer as Network
Independent Layer and Session Layer, Presentation Layer, Application Layer as Upper Layers.
- Also, these layers
are sequenced in fixed manner and this sequence cannot be changed. It means,
any alterations in the positions of the layers are not accepted.
Computer Network Models
: Architecture And Layers of OSI Reference Model
A) The Physical
Layer
- The Physical Layer is the bottom most layer and is associated with electrical, mechanical and
functional aspects of the transmission media for information and receiving over
internet.
B) The Data
Link Layer
- The Data Link Layer is second from bottom and
comes under the lower layer category. It ensures that the data must be
synchronized, error detection and control are enabled.
C) The Network
Layer
- The Network Layer is third from bottom in OSI
model and is responsible for establishing data communication channel between
multiple networks or devices or hosts or nodes.
D) The
Transport Layer
- Transport Layer is the middle most layer in
OSI model and it acts as Network Independent Layer. It has no idea about the
functioning of lower layer i.e. physical, data link and network
layers.
E) The Session
Layer
- Session Layer is the fifth layer of OSI model
and it provides appropriate sessions between users and entities, where user
interacts. This layer can be used on the basis of resources available and it
can be skipped too if not required.
- For example : Login Sessions in online
banking.
F) The
Presentation Layer
- This is the sixth layer of OSI model and it
provides appropriate representation of data through various data
presentation techniques.
G) The
Application Layer
- Application Layer is
the topmost layer of the OSI model and has the responsibility for providing
interface between various users and application.
Computer Network Models
: Advantages Of OSI Model
- The OSI Model being
one of the most widely used computer network models does posses some major
advantages which makes it so popular. These are :
- Each layer has its definite structure
and functionality which makes OSI model simple and easy to
use.
- It is a general purpose reference
model that can be used for data communication.
- Connection oriented
and connection-less services are supported.
- Connection between any type of devices
or host or hardware or software is possible.
Computer Network Models
: Disadvantages Of OSI Model
- Because of its
inability to fit protocols, this model was replaced by TCP/IP Internet
Model.
- Session and
Presentation layers does not provide high end functionalities and are not of
much use as compared to other layers.
- Connection oriented
and connection-less services are supported.
- Connection between
any type of devices or host or hardware or software is
possible.