What is an OSI Model ?
OSI or Open System Interconnection Model was developed by International Organization
for Standardization in the year 1984 for easy and reliable Network Communication.
In other words It can de said that this model basically facilitate to send and receive
messages from one computer to another computer in a network smoothly ans hassle free.
Basically OSI or Open System Interconnection is composed of Seven Layers to transmit
data from one computer to another across the globe
It may be noted that OSI layer is a reference layes in network communication and is
and it is used practically to visualize and communicate how network operates.
The layers of OSI Model from the sender end is as follows:
1st Layer - Application layer:
2nd Layer- Presentation layer
3rd Layer - Session layer
4th Layer- Transportation layer
5th Layer- Network layer
6th layer- data Link layer
7th layer - Physical layer
The layers of OSI Model from the receiver's end is as follows:
7th Layer - Application layer:
6th Layer- Presentation layer
5th Layer - Session layer
4th Layer- Transportation layer
3rd Layer- Network layer
2nd layer- data Link layer
1st layer - Physical layer
Let us see the OSI layers in detail:
Basically the OSI layer is practically divided into 2 layer
Upper layer: The upper layer is composition of Application layer,Presentation layer
and the Session layer. This layer is also called as software layer.
Lower layer: The Lower Later is a composition of Physical layer, data link layer
and Network layer.
The Transport Layer is basically the Heart of the OSI layer.
1. Physical Layer:This layer includes the Physical equipments included in data
transfer from one computer to another computer such as cables, switches.
In this layer the data get converted into bit stream.The Physical layers converts
the data in the form of 0's and 1's and transmit it from one node to another.
This layer is the lowest layer in the OSI reference model.
2. Data Link Layer: The Data Link layer is responsible to convert the data in
frames which it has received form Network layer. and send it from one computer
to another computer in the same network.This layer is responsible error free
transfer of data from one node to another using its MAC address of the nodes.
The packets received from the Network layer are broken down into smaller
pieces called frames.The Data Link is composed of two sub parts:
1.LLC- Logical Link Layer which is responsible for error free transmission
and synchronizing frames and managing protocols
2.MAC- Media Access Control which is responsible for connecting devices
in a network and transmit and receive data
3. Network Layer:This Layer is similar to the Data link layer except that it is used
to send data packets by breaking the segments received from Transport layer
from one node to send it to another node by reassembling it in receiver's ends
in different network.It sends packet by selecting the shortest path which is
available in the Network,
4. Transport layer.This layer is also known as the Heart of the OSI layer. This layer
is responsible for reliable and end to end delivery of the message This layer
receives the data and breaks it in form of segments at the sender's end.
It also adds source and destination port number and forward the segmented data
to the Network layer.It is used fro checking error control if present and retransmit
back to the source to send it again to the destination.
5. Session Layer:This layer is responsible for setting communication between two
devices in a network.This layer ensures that the data is exchanged properly
between the two nodes during the ongoing session and then automatically closes
the session to avoid wastage of resources.
The Session layer has also set benchmarks to identify the errors and avoid premature
loss of data if the session is closed before delivery to receiver's end which is also
known as Synchronization of data .
6. Presentation Layer;This layer is responsible for translation of data in the required
format over the network and is also used for encryption and decryption of data
so that the data is end securely from sender's end to the receiver's end. It is also
used to compress the data bits as per the requirement of the receiver.
7. Application Layer: This layer is responsible for directly Interacting with the
user for the data using software application like Browsers, email , messengers.
This layer is responsible for the protocols and data manipulation to present
meaningful data to the user through the software applications.
No comments:
Post a Comment