CCNA - OSI reference model

7 layers seperate functionalities in order to allow developers to design applications that are capable of running on virtually any system type or network.

Specific tasks are assigned to each layer, no layer is supposed to interfere with the tasks of another layer, but neighbouring layers must of course interface.

7: Application

6: Presentation

5: Session

4: Transport

3: Network

2: Data Link

1: Physical

7

Application

HTTP, FTP, SMTP, ...

6

Presentation

Data translations, code formatting, encryption, compression

EBCDIC, ASCII

5

Session

4

Transport

TCP, UDP, flow control, windowing

Firewalls

3

Network

IP

Router

2

Data Link

Ethernet, MAC, LLC

Switch, Bridge

1

Physical

Cat5, UTP, el. coding, coax

HUB

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Subtopics: 1: Physical Layer 2: Data Link Layer 3: Network Layer 4: Transport Layer 5: Session Layer 6: Presentation L. 7: Application Layer