OSI MODEL

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WHAT IS OSI LAYER?


 OSI means OPEN SYSTEM INTERCONNECT model or layer.it means every System is open to connect with other.

# Developed by ISO (INTERNATIONAL ORGANIZATION FOR STANDARDIZATION)
IN 1974.

#It consist  of seven layer.


#Each layer has a different but specific processing function.

 Layer 7>>APPLICATION
Layer 6>>PRESENTATION
Layer 5>>SESSION
Layer 4>>TRANSPORT
Layer 3>>NETWORK
Layer 2>>DATA LINK
Layer 1>>PHYSICAL


7.)APPLICATION LAYER

it provides networking services to user.
It also known as desktop layer.
protocols like dhcp,http,webbroweretc are used in this layer.


6.) PRESENTATION LAYER

It converts data into standard formats for to receive or transmit.
(American standard code for information interchange)
e.g.>>ASCII,JPEG,BMP,MP3 etc.

following tasks are done in this layer
ENCODING – DECODING
ENCRYPTION - DECRYPTION


5.) SESSION LAYER

It is responsible for establishing,maintenance,and terminating session.

SESSION ID WORKS IN THIS LAYER.
E.G.-
RPCàREMOTE PROCEDURE CALL
SQLàSTRUCTURED QUERY LANGUAGE
NFSàNETWORK FILE SYSTEM




4.)TRANSPORT LAYER

IT maintains END TO END connectivity.
It is the heart of OSI LAYERS.
Two protocols works in this layer they are-

1.      TCP (TRANSMISION CONTROL PROTOCOL)
2.       UDP (USER DATAGRAM PROTOCOL)

FOLLOWING TASKS ARE DONE HERE

# IDENTIFYING SERVICES.
# MULTIPLEXING & DE-MUX.
# SEGMENTATION.
# SEQUENSING & REASSEMBLING.
# FLOW CONTROL.
# ERROR CORRECTION.

3.)NETWORK LAYER

IT provides best path for data to reach destination.
Logical addressing is done on this layer.
Device works on this layer is router.

It is divided into two parts

1. routed protocols
e.g. ip,ipx,apple talk etc.

2. routing protocols
e.g. rip >routing information protocol
ospf>open shortest path first
igrp>integrated gateway routing protocol
eigrp>enhance igrp

2.) DATA LINK LAYER 

It is divided into two sub layers.
 1. LLC –LOGICAL LINK CONTROL
WAN protocols works here.provides error-free data from one node to other node.
e.g. ppp(point to point protocol),hdlc(high level data link control).

2. MAC – MEDIA ACCESS CONTROLLER.
It talks about physical address.




1.)PHYSICAL LAYER 

It talks about electrical,mechanical or procedural checks.
Co-axial or twisted pair cable> data will be in electrical pulse or e- form.
Fiber optic cable>>data will be in light form.
Devices works in this are>>
ethernet
Hubs (active & passive)
Cables
repeaters
connectors

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