OSI Reference Model Layer Summary

8/17/2019 OSI Reference Model Layer Summary

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OSI Reference Model Layer Summary

Group # Layer Name Key ResponsibilitiesData TypeHandled

Scopeommon !rotocols and

Tec"noloies

Lo$er Layers

% !"ysicalEncoding and Signaling; Physical DataTransmission; Hardware Specifications;

Topology and DesignBits

Electrical or lightsignals sent

between localdevices

(Physical layers of most of thetechnologies listed for the data

link layer

& Data Lin'

!ogical !ink "ontrol; #edia $ccess "ontrol;Data %raming; $ddressing; Error Detection

and Handling; Defining &e'irements of Physical !ayer

%rames

!ow)level data

messages betweenlocal devices

*EEE +,-.- !!"/ Ethernet%amily; Token &ing; %DD* and

"DD*; *EEE +,-.00 (1!$2/ 1i)%i; HomeP2$; Home&%; $T#;

S!*P and PPP

( Net$or'

!ogical $ddressing; &oting; DatagramEncapslation; %ragmentation and&eassembly; Error Handling and

Diagnostics

Datagrams 3Packets

#essages betweenlocal or remote

devices

*P; *Pv4; *P 2$T; *Psec; #obile*P; *"#P; *P5; D!"; P!P;

&oting protocols sch as &*Pand B6P

) Transport

Process)!evel $ddressing;#ltiple7ing3Demltiple7ing; "onnections;

Segmentation and &eassembly; $cknowledgments and &etransmissions;

%low "ontrol

Datagrams 3Segments

"ommnicationbetween software

processes

T"P and 8DP; SP5;2etBE8*32B%


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*pper Layers

+ SessionSession Establishment/ #anagement and

TerminationSessions

Sessions betweenlocal or remote

devices

2etB*9S/ Sockets/ 2amedPipes/ &P"

, !resentation Data Translation; "ompression andEncryption Encoded8ser Data $pplication datarepresentations SS!; Shells and &edirectors;#*#E

- .pplication 8ser $pplication Services 8ser Data $pplication data

D2S; 2%S; B99TP; DH"P;S2#P; \ %TP; T%TP;S#TP; P9P:; *#$P; 22TP;

HTTP; Telnet

Understanding it through real life example is kinda dicult but suppose you're carrying large amount of goods from one place to other.

Say you're travelling in sea using a number of ships.

1. Physical Layer: Physical layer deals with the actual connectivity between the source and destination. f you're transferring data to

another machine through !"#$ physical layer is the %thernet connection. &he water in the sea connecting your place and destination is the

physical layer in our case.

. Data Link layer: n this layer data is broken down into pieces. &hat is your goods will be separated in various categories$ say expensive

goods$ fragile and non fragile. &his layer deals with breaking the data being sent and transmitting it through the physical layer. So goods

being categori(ed and sent through the sea.

). Network layer: *ere the data being sent is organi(ed. t also decides which protocols to use$ tcp or udp. So in our case the di+erent

compartments of ship where you'll keep these goods is the network layer. t will also decide which generators and engines to be used

while travelling ,protocols-.

. Transport Layer: &ransport layer gives you the best route$ security and safest path to the destination. &he transportation of data takes

place here. So think of the coast guard as transport layer. *e'll look after the connection$ inform you if there's any danger and tell you the


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best route to your destination.

/. Session layer: &he best way to remember a session is thinking of it as a *angout or 0ahoo messenger chat. hen two people start

communicating a session is created$ as soon as one ends the chat or disconnects session is broken. Session layer creates a new session

for a pack of data. So the time when our ships leaves our docks and till the time it reaches the destination is one whole session$ assuming

there are no problems during that interval. f your ships gets hi2acked by pirates$ session is terminated. f the destination blows up$ session

is terminated.

Session plays an important role in online transactions. n the very last step$ where you need to enter 3&P or your secure password toauthori(e the transaction$ if you sit idle for more than 4) minutes without any activity$ the session will terminate itself and the transaction

will be unsuccessful.

5. Presentation Layer: &here are times you send various 6le formats through the network like images or videos. Presentation layer deals

with all this di+erent 6les. t converts this data into a readable format for the destination. &hink of a captain who's in charge of people from

various races$ countries and languages. *e has to make sure everyone will reach to destination and can perform their work over there.

7. Application layer: 8any people think of browsers as soon as they hear application layer. 9ut application layers isn't the browsers or

application you're using. n our case if browsers are taken then ships will be out application layer.

9ut application layer is not the browser but the common protocols used by the browsers. So application layer are not the ships but thecommon fuels these ships are using.

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OSI Reference Model Layer Summary