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preface

Public number to NPY front – end esoteric

Add vx👉16639199716, pull you into the group Ow ~❤️

What do we need to do for an interview?

  1. Master computer networkBasic concepts, principles and methods.
  2. Master computer networkarchitectureAnd typicalNetwork protocol. To understandTypical network equipmentTo understand the working principles of typical network devices.
  3. Be able to use the basic concepts, principles and methods of computer networksAnalysis, design and application of network systems.

This column will comb through the knowledge involved in the computer network interview and study 👍👍👍

In the last article, we gave you an overview of computer networks, so this article will take you through the architecture and the reference model 👇

Review last issue

An overview of computer networks we can read an article

Previous article: 😁 Front-end needs to know computer network knowledge, this column is enough!

One, layer, protocol, interface, service

Why stratify?

  • The computer initiating the communication must activate the data communication pathway
  • Tell the network how to identify the destination host
  • Check whether the destination host is started and connected properly
  • Whether the file management program on the other party’s computer has been prepared
  • Errors and accidents can be solved

entity

Active elements in layer N are called Layer N entities, and entities in the same layer are called peer entities

agreement

Rules, standards, or conventions (horizontal) established for the exchange of data between peer entities in a network

There are three aspects to the agreement

  • grammar: Specifies the format of the data to be transmitted
  • The semantic: Specifies the function to be performed
  • synchronous: Specifies the order of various operations

interface

The upper layer uses the entry of the lower layer services

service

Function calls provided by lower layers for adjacent upper layers (vertical)

Characteristics of stratification

  1. Each layer is independent of each other, and each layer implements only one relatively independent function
  2. The interface between each layer is naturally clear and easy to understand, with minimal interaction
  3. The lower layer is independent from the upper layer. The upper layer uses the services provided by the lower layer in one way
  4. Structurally separable, using the most appropriate technology for each floor

😁 Summary: Computer network architecture is a collection of layers and their protocols in a computer.

OSI Reference Model

The seven-layer model is mainly divided into:

  • The application layer
  • The presentation layer
  • The session layer
  • The transport layer
  • The network layer
  • Data link layer
  • The physical layer

Each layer provides services to the upper layer and receives services from the lower layer. The lower layer is oriented toward the lower layer and the higher layer is oriented toward the users.

Important: 😁

When host A transfers data to destination host B through the intermediate system, the upper four layers are end-to-end and the lower three layers are point-to-point

The reason is that the intermediate system can only use the physical layer, data link layer, and network layer at most.

It is worth noting that the transmission of data is equivalent to a series of behaviors which are packaged and mailed by the express merchant and then unsealed when we receive the express. No discussion here…

Functions of each layer and typical protocols

The application layer

Any program that interacts with users and generates network traffic

Typical application layer services:

  1. File Transfer (FTP)
  2. Email (SMTP)
  3. World Wide Web (HTTP)
The presentation layer

The presentation (syntax and semantics) used to deal with the exchange of information between two communication systems

Function 1: Data format transformation (translator)

Function 2: Encrypts and decrypts data

Function three: Data compression and recovery

The session layer

To provide the presentation layer entity/user process to establish a link and orderly transfer data on the connection (establish synchronization SYN) function 1: establish, manage, terminate sessions

Function 2: If the session fails to communicate with the parity point, the session can resume communication from the parity point and implement data synchronization. (Suitable for large file transfer)

The transport layer

It is responsible for the communication between two processes on a host, that is, end-to-end communication. The transmission unit is packet segment or user datagram. Function 1: Reliable transmission (TCP), Unreliable transmission (UDP)

Function 2: Error control

Function 3: Flow control

Function two: reuse and division

The network layer

Main tasks: Transfer packets from remote end to destination end, providing communication services for different hosts on the packet switching network. The transmission unit at the network layer is datagram. Function 1: Route selection

Function 2: Error control

Function 3: Flow control

Function 2: Congestion control

Data link layer

The main task is to assemble the datagram from the network layer into frames. The transmission unit is a frame

Function 1: Framing (define the beginning and end of a frame)

Function 2: Error control

Function 3: Flow control

Function four: Access access control

The physical layer

The transparent transmission of bitstreams, in bits, over physical media

Function 1: Define interface features

Function 2: Define the transport mode

Function 3: Define the transmission rate

Function four: Bit synchronization

Function 5: Bit coding

conclusion

The first column with you to learn the basic knowledge of computer network, the follow-up will be more wonderful wow, come on together wow ~

❤️ Thank you all

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