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3.3 The OSI Reference Model
(Эталонная модель Open Systems…
3.3 The OSI Reference Model
(Эталонная модель Open Systems Interconnection)
Please Do Not Throw Sausage Pizza Away
Layer 1: The Physical Layer
- data transmission over the hardware, including line codes, modulation techniques, and connector and cable types
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Level 2: Data Link Layer
- connects the line codes of the first layer with the channel encoding for error detection and forward correction
- media access control protocols
- MAC address + MAC address switches (уникальный идентификатор, присваиваемый каждой единице активного оборудования или некоторым их интерфейсам в компьютерных сетях Ethernet), (it's written in hexadecimal form)
- позволяет идентифицировать каждую точку подключения, каждый узел сети и доставлять данные только для корректной передачи данных и предоставления услуг
12-34-56-78-9a-bc
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Level 3: The Network Layer
- logical addressing
- path deyermination
- routing
- level 3 switches, which switch between data link domains (-участники могут обратиться к каждому участнику напрямую через MAC или аппаратные (hardware) адреса)
- data units aka segments after transmission to level 3 are called as data packets
Logical addressing
- IPv4 and IPv6
- every computer has unique IP address
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Level 5: The Session Layer
- helps in setting up and managing connections to send and receive the data
- API's (application programming interface) - like helpers, which help to manage tasks concerned connections
-before server or connection is established, server performs authentication and then authorization
- data packets go to computer from the web server
browsers performs level 7, 6, 5
Layer 6: The Presentation Layer
- receives data from Application Layer, the data is in the form of letters and numbers
Presentation layer converts the data --> to binary code (Translation)--> reduces the number of bits (Data compression) --> enhance data security (Encryption/Decryption)
Data compression
Can be:
- lossy or lossless
- reduces the amount of space used to store the original data, to speed up the delivery process
Encryption
- enhance data security
sender: data is encrypted
receiver: data is decrypted
- SSL protocol is used
Level 7: The Application Layer
- Network Application uses application layer protocols - HTTP, HTTPS etc (Network Application - applications that use the Internet: browsers, skype etc)
- These protocols provides such functions as: file transfer, web surfing, emails etc
- Layer provides services for network applications with the help of protocols to perform user activities
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