Vernacular TCP/IP protocol

This article is inspired by a PPT document downloaded from the Web

Before using the network

I have a payroll report that needs to be printed, but I don't have a printer.
Play the spirit of indigenous steelmaking, through a U disk copy to another computer.

History of the computer network

The 50 's: the computer network preliminary formation, the goal is to share resources;
60 's: The United States Department of Defense invented the ARPANET,TCP/IP agreement appeared;
70 's mid-term: LAN development quickly, small and medium-sized enterprises can also form their own network;
90 's: The era of Internet rapid development, we have today's network

What is a network

A computer network is a collection of computers connected together
Means: connected by communication devices and communication lines, and managed using network software and protocols
Objective: To achieve the goal of resource sharing

Communication equipment: Hubs, switches, routers, ADSL modems, including SPC switches, etc.
Communication line: Twisted pair, telephone line, optical fiber, radio wave, etc.

TCP/IP Protocol

A metaphor for communication protocols

To complete the task-communication: Shenzhen's Mister A to tell Beijing's Mister B: Goods have been issued.
A write a letter in Chinese; give the letter to the Secretary; The post office chooses the delivery route of the letter according to the addressee's address; The station is responsible for transporting the letters to Beijing;
After receiving the letter from the railway station in Beijing, what is the next step. b How to receive information.

Analysis of the above examples (1)
Purpose: to communicate
is how to complete the communication.
Everyone follows certain rules.
A write a good letter in a certain format
The secretary filled out the address on the envelope.
The Post office sends messages based on how the messages are processed
The railroad has its own way of working.
Each of the above work together, rely on each other, accomplish the same thing: communication

Analysis of the above examples (2)
Clear division of Labor
The secretary just needs to know to drop the letter in the mailbox.
The postman doesn't have to drive a train.

Computer Communication Protocol (PROTOCOL)
Purpose: Complete computer communication (communicate)
What is a protocol: a set of rules for a computer to communicate
The rules specify how different devices should work together to ensure data transfer to each other

OSI model
Describes the functions of different devices in the communication process
Actually, it also sets out how different devices work together.
Presented by ISO (International Organization for Standardization)
Determining standards for network devices

Layered
Tiering is usually a good way to solve complex problems
Layering means division of labor.
3 major benefits of tiering:
Each layer is independent, one layer of change does not affect other layers
Easy to implement and maintain
Advantageous standardization: the equipment of different factories can coexist

Determine how to use the contact email (POP3) or ordinary letter

-- [ Application Layer (application)] : interface between the user application and the network

Credit is written in Chinese or English.

-- [ Presentation Layer (presentation)] : Encode data, compress data, encrypt data

Before the two sides communicate to make rules, when to start, terminate.

-- [ Session layer] : Allows users to establish, maintain, and terminate sessions between devices

The secretary found that the other party did not receive the letter, whether to send another letter.

-- [ Transport Layer (transport)] : provides reliable (or unreliable) end-to-end services. Flow control.

From what line is sent to Beijing.

-- [ Network Layer (network)] : addressable: How to represent different computers. For example: IP address. Choose the best

The path transmits information from the most appropriate path to the receiving end.

The post office will cover the letter with a postmark.

-- [ Data Link layer] : The encapsulation of frames: the transmission of data to increase the synchronization of information, checksum information and address information encapsulated into a data frame.

The letter is pulled by train or by car.

-- [ Physical Layer (physical)] : responsible for 0 and 1 of the transmission, the use of what transmission media, 0 and 1 on the line to indicate how the line of the connector is what.

TCP/IP Reference Model/DOD model (DOD: U.S. Department of Defense)

[ Application Layer (application)]

[ Transport Layer (transport)]

[ Internetwork (Internet)]

[ Network access layer (network access)]