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One 、 Preface

This is ESP8266 Some skills in learning , Examples of nouns and procedures

Two 、 Noun

1.Mac

Mac： The unique network address of the network card device in the network . Uniformly distributed by the hardware manufacturer , Of every computer MAC The address is unique ;
MAC Address ： The address used on the data link layer , It's also called physical address 、 Hardware address or link address , Written inside the hardware when produced by a network device manufacturer .

2. gateway IP Address

Everybody knows , From one room to another , It must pass through a door . Again , Send messages from one network to another , You have to go through one “ Gateway ”, This gateway is the gateway . seeing the name of a thing one thinks of its function , gateway (Gateway) It's when one network connects to another “ Gateway ”.
Without a router , There's no way between two networks TCP/IP communication , Even if two networks are connected to the same switch ( Or hubs ) On ,TCP/IP The protocol will also be based on the subnet mask (255.255.255.0) Determine that the hosts in two networks are in different networks . And to achieve communication between these two networks , You have to go through the gateway . If the Internet A The host in found that the destination host of the packet is not in the local network , Just forward the packet to its own gateway , And then the gateway forwards it to the network B Gateway for , The Internet B And then forward it to the network B Some host of ( As shown in the attached figure ).

3. Subnet mask

1、 For shielding IP Part of the address to distinguish between a network ID and a host ID , And explain the IP The address is on the LAN , Or on the Internet ;2、 Used to put a large IP The network is divided into several small subnetworks .
Subnets are used to reduce IP Waste of . Because with the development of the Internet , More and more networks come into being , Some networks have hundreds more , There are only a few , This wastes a lot of IP Address , So we need to divide the subnet . Using subnets can improve the efficiency of network applications .

4.DNS

Resolve the domain name to IP Address , Domain name and IP The addresses are linked Carry out services , So you don't have to enter IP Address , Instead, you enter the URL to access the site .

5.hots

Put some common URL domain names and their corresponding IP The address establishes an association “ database ”, When the user enters a web address to log in in the browser , The system will automatically start from Hosts Look for the corresponding IP Address , Once found , The system will immediately open the corresponding web page , If not found , Then the system will submit the website again DNS Domain name resolution server IP Address resolution .

6.SSID

SSID Technology can divide a WLAN into several sub networks that need different authentication , Each subnetwork needs independent authentication , Only authenticated users can enter the corresponding subnet , Prevent unauthorized users from entering the network .
In layman's terms ,SSID That's the name you give your wireless network .

7.client and Server

Server Ask for my
client To request data from others, for example ： The weather

8.TCP

1.TCP agreement

TCP Protocol is connection oriented communication protocol , That is to say, before data transmission, a logical connection is established between the sender and the receiver , Then transfer the data , It provides reliable and error free data transmission between two computers .

stay TCP The client and server must be specified in the connection , The client sends the connection request to the server , Every time a connection is created, it needs to go through “ Three handshakes ”.

The first handshake , Client sends connection request to server , Wait for server to confirm

The second handshake , The server sends a response back to the client , Notify client that a connection request has been received

The third handshake , The client sends the confirmation information to the server again , Confirm connection

2.TCP Communications

Once the connection is established ,TCP The protocol provides full duplex communication services . It's called full duplex , intend ： At the same time in the same link , Both sides of the communication can write data at the same time . The concept of relativity is called half duplex , namely ： At the same time in the same link , Only one party can write data .
（1） Server slave accept Function is called immediately after it returns read Function reading socket The data in . read socket It's like reading a pipe , If there's no data coming, block and wait .
（2） Client calls write Function to send a request to the server , The server will reply to the client after receiving ACK, And from read Function , Process the client's request . In the meantime, the client calls read The block function waits for a response from the server .
（3） Server calls write Function sends the processing result back to the client , The client will reply after receiving ACK. The server calls... Again read Function block waiting for next request ,.
（4） The client from read Function , And send the next request , Go on like this .

9.http

10.UDP

/**

• Start to create a message that needs to be sent to the remote host udp package
• @param ip Remote host ip Address
• @param port Remote host port number
• @return 1 Create success

•     0  Create failure 
  

*/

int beginPacket(const char *host, uint16_t port);