OSI Model animated, What is osi model in networking? 7 OSI layers explained

the osi model describes how a data

transfers over the network from one

computer to the other

and the way the systems send information

to one another

in order to accomplish a successful

communication between computers

there are seven distinct layers which

are interconnected

and which work closely to make the

communication happen

that is why it is called the open system

interconnection model

or the osi 7 layer model

the purpose of this model is to enable

functionality and interoperability

between

different vendors and connectors

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from a design point of view it divides

larger tasks into smaller

more manageable ones

the seven layers of osi model are

layer one physical layer

layer two data link

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layer three network

layer 4 transport

layer 5 session layer 6

presentation layer 7

application

data flow example this is how data flows

through the osi model

for example if you send an email to a

colleague or friend

your email has to pass to presentation

layer via

application layer the data gets

compressed at this layer

next is the session layer which

initializes communications

it will then be segmented in the

transportation layer

broken up into packets in the network

layer and then into frames in the data

link layer

it will then be sent to the physical

layer where it is converted to zeros and

ones and

sent through a physical medium like

cables

when your friend gets the email through

the physical medium

the data flows through the same layers

but in the opposite order

the physical layer will convert the

zeros and ones to frames that will be

passed to the data link layer

this will reassemble the frames into

packets for the next layer

the network layer will assemble the

segments into data

the data is then passed on to the

presentation layer which ends the

communication session

the presentation layer will then pass

the data to the application layer

the application layer feeds the human

readable data to the email software that

will allow your friend to read your

email

application layer the application layer

is where the user

interacts with the software application

so it is closest to the end user

this layer interacts with the

application communicating with the

network

application layer is used by network

applications which rely

on application layer protocols like http

and https to function the applications

that use these protocols are browsers

firefox google chrome outlook skype

etc there are many application layer

protocols that enable functions at this

layer

all these protocols collectively called

application layer

application layer provides services for

network applications

with the help of these protocols users

are able to perform activities like

sending emails file transfer web surfing

etc

file transfer is done with the help of

ftp protocols

for sending emails smtp protocol is used

web surfing is done with the help of

http or https protocol

and for virtual terminals telnet is used

application layer provides services for

network applications

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presentation layer next to application

layer

is the presentation layer this layer is

responsible for ensuring that the data

is understandable for the end system or

useful for later stages it translates or

formats data based on the application

syntax or semantics it also manages any

encryption or decryption required by the

application layer

it is also called the syntax layer

next to application layer is

presentation layer

presentation layer receives data from

application layer and converts

conversion of ascii code to machine code

or language

this function of presentation layer is

called translation

encryption enhances the security of

sensitive data at sender side

data is encrypted at the receiver side

data is decrypted as protocols or secure

sockets layer protocol

is used in presentation layer for

encryption

and decryption so presentation layer

performs three basic functions

transmission compression and encryption

decryption

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session layer the session layer will

create communication channels

called sessions between different

devices

this layer is responsible for opening

those sessions and ensuring that they're

functional during data transfer

in other words the session layer is

responsible for establishing

managing and terminating communication

sessions with the lower layers with the

presentation and communication layer

it is also responsible for

authentication and reconnections

and it can set checkpoints during a data

transfer

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transport layer the transport layer is

responsible for delivering

error checking flow control and

sequencing data packets

it regulates the sequencing size and

transfer of data between

systems and hosts it gets the data from

the session layer and breaks it into

transportable segments

protocol from transport layer or

transmission control protocol

or tpt and user datagram protocol

or udp transport layer performs two

types of services

connection oriented transmission and

connectionless transmission

connection oriented transmission is done

via wire connection

this transmission is done by udp

udp is faster than tcp because it does

not provide any

feedback whether data has really

transferred whereas tcp

provides a feedback therefore

load data can be retransmitted in tcp

layer 3 network layer

the network layer receives frames from

the data link layer

and delivers them to the intended

destination based on the addresses

inside the frame

it also handles packet routing the

network layer locates destinations using

logical addresses like the ip

routers are a crucial component at this

layer as they route information to where

it needs to go

between different networks

the main functions of the network layer

are

routing the network layer protocols

determine which routes from source to

destination

logical addressing the network layer

defines an addressing scheme to uniquely

identify devices

the network layer places the ip

addresses from the sender and receiver

in the header

layer 2 data link layer

the data link layer corrects any errors

that may have occurred at the physical

layer

it ensures that any data transfer is

error free between nodes over the

physical layer

it is responsible for reliable

transmission of data frames between

connected nodes

the data is packaged into frames here

and transferred

node to node the data layer has the

following sub

layers media access control

mac the mac address layer is responsible

for flow control

and multiplexing devices transmissions

over the network

logical link control llc

the llc layer provides error control and

flow control over the physical medium

and identifies line

protocols layer 1

physical layer the physical layer is

responsible for transmitting

unstructured data bits across the

network

at the lowest layer of the osi reference

model between the physical layers of the

sending

and receiving devices in other words

it takes care of the transmission of raw

bit streams

the physical layer may include physical

resources like cables

modems network adapters and hubs etc