* Communication between two computers is a communication process between two computers .
* Network classification :
LAN,WAN,WLAN
LAN (Local Area Network,LAN)
Wan Wide Area Network,WAN)
WLAN (Wireless LAN,WLAN)
<>TCP/IP Brief introduction

*
agreement : Rules of communication between two parties / regulations
Figurative metaphor :
Chinese people need to follow the standard of Chinese discourse meaning when communicating with each other
Foreigners should follow the standard of foreign discourse meaning in communication with each other
Computer communication needs to follow the standard of computer semantics
This semantic standard is called protocol

*
Hundreds of Internet protocols , The two most important agreements are TCP and IP agreement , So the Internet Protocol abbreviation TCP/IP agreement .
TCP/IP It's a protocol family
The protocol specifies how the data should be encapsulated , Addressing , transmission , Routing and receiving at destination .

*
TCP/IP There are two big classification models :
International Organization for Standardization (ISO) Of OSI Model , The open communication system interconnection reference model (Open System Interconnection Reference
Model), application layer <–> Presentation layer <–> Session layer <–> Transport layer <–> Internet layer <–> link layer <–> physical layer
Simplified four layer model : application layer <–> Transport layer <–> Internet layer <–> physical layer

There are standard hierarchical boundaries In order to have professional people to do professional things Or we do the Internet , It may also be necessary to understand how photoelectric signals are converted :(

* link layer : Handle physical interfaces with cables or other transmission media
* network layer : The activity of processing data in the network
<>ip agreement 【 Network interconnection protocol 】

purpose : Connecting multiple packets across the network , Transmit packets ( Unreliable transmission ), The most basic function is addressing and segmenting , End to end is not available , Route to route confirmation , No retransmission and flow control . It is the basic rule that computer network can communicate with each other . Mistakes are like ICMP report ,
ICMP stay IP Module

<>ICMP agreement

purpose : Connectionless protocol oriented , Used to transmit error report control information ( Control information refers to the network is not smooth , Does the host arrive , Whether routing is available for these network itself messages , Data transmitted by users is not involved )

<>ARP agreement -> Address resolution protocol

purpose : according to IP Address a protocol for obtaining physical address ( Namely MAC address ). In the same subnet ARP The protocol can transfer data packets to each other . If it is not in a subnet, it cannot be obtained MAC address , Only through the gateway .

<>RARP agreement -> Reverse address protocol

purpose : and ARP On the contrary , Convert the physical address of the host to IP address .
Transport layer : Provides end-to-end communication between two hosts

<>TCP agreement -> Transmission control protocol

purpose : Connection oriented , Ensure high reliability ( No data loss , No data out of order , No error in data , No repeated data arrival ) Transport layer protocol .

<>UDP agreement -> User data protocol

purpose : No connection , Unreliable transport layer protocol .
application layer : For different applications

<>NAT agreement -> Network address translation protocol

purpose : Realize Intranet IP Conversion between address and public address . Will be a lot of intranet IP Convert to one or a few public networks IP

<>FTP agreement -> File transfer protocol

purpose : adopt FTP Agreement in FTP Client access FTP Server , Default use 20 and 21 port ,20 For data transfer ,21 Used to transmit control information .

<>HTTP agreement -> Hyper Text Transfer Protocol

purpose : Is used from WWW Transmission protocol of hypertext from server to local browser . Is a client browser or other program associated with Web Between servers
Application layer communication protocol .

<>TELNET agreement

purpose : yes Internet Standard protocol and main mode of remote login service , It provides users with the ability to complete the remote host work on the local computer .

<>SMTP agreement -> Simple Mail Transfer Protocol

purpose : Rules for controlling mail transmission , And how to transfer mail .

<>DNS agreement

purpose : Define domain name rules , Add domain name and IP Mutual mapping

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