Summary of WLAN related knowledge points

1 The background

• The laying cost of wired transmission medium is high , Fixed position , Poor mobility
• People are increasingly demanding the portability and mobility of the network

2 Related knowledge

2.1 WLAN Basic concepts of

• wireless LAN（ WLAN ）, It means passing through Wireless technology Build a wireless local area network .
• WLAN In a broad sense, it refers to the use of radio waves 、 laser 、 Infrared and other wireless signals to replace part or all of the transmission media in the wired LAN network .
• WLAN yes Computer network and wireless communication technology （Wi-Fi） Combination The product of , It is the wireless extension of wired network .
• The cat used at home is WiFi technology . Now most of WLAN It's used WiFi,
  Traditional networks ： | Wired , The terminal cannot be moved at will |
  Wireless network ： | Switch 、 Router | AP（access point） Access points | Can move freely |

2.2 Wi-Fi：

• Wi-Fi It's based on IEEE 802.11 Standard WLAN technology .
• In everyday life , Regular general Wi Fi treat as 802.11 A synonym for .
• Wi-Fi It's also Wi-Fi Trademark of alliance manufacturer , And as a Wi-Fi Brand certification of products .
• Wi-Fi The alliance was founded in 1999 year , It was called Wireless Ethernet Compatibility Alliance（WECA）. stay 2002 year 10 month , Officially renamed Wi-Fi Alliance.

WI-FI The development trend of office scene ：

2.3 IEE 802 And TCP/IP peer model

WLAN It's based on IEEE 802.11 Standard WLAN technology .
802.11 Standards focus on TCP/IP The lower two layers of the peer-to-peer model ：
** Data link layer ：** Mainly responsible for channel access 、 Addressing 、 Data frame verification 、 Error detection 、 Security mechanism .
** The physical layer ：** Mainly responsible for empty port （ Air interface ） Medium transmission bit stream , For example, specify the frequency band used .

2.4 IEEE 802.11 Standards and Wi-Fi The generation of

3 Networking architecture

The terminal is connected to AP, During a visit to Internet.

3.1 fat AP framework

1. Wireless control operation and function are in AP The complete , for instance ：SSID The name of wireless signal is from AP released ,SSID Your password is also in AP The configuration of ,IP The address is also by AP Distributed , fat AP It can be understood simply as doing everything . The router at home is fat AP
2. Simple configuration 、 Single function
3. Suitable for home use

3.2 AC+ Thin AP framework

1. AP Is the access point ,AC Access controller ,**AP Its main function is to send RF signals , Encryption of message , And some physical layer functions
2. Wireless related things , such as ：SSID、 Means of encryption 、 Encrypted key 、DHCP It's not AP In charge of , But by the AC be responsible for .
3. AP It's like a middleman , Just forward it .
4. Apply to ： Management of enterprise parks , Because you can get through AC Conduct a centralized management .SDN The architecture of is very similar AC+AP This architecture .AP Often connected to the access layer switch .

4 Networking concept

4.1 Wired side networking concept

AP-AC Networking mode

AC How to connect

AC and AP Through between CAPWAP Tunnel interaction , Including some configuration
stay AC On dis ap all You can view subordinates AP The state of

CAPWAP agreement

CAPWAP（Control And Provisioning of Wireless Access Points Protocol Specification, Wireless access point control and configuration protocol ）： The agreement defines how to AP Conduct management 、 Business configuration , namely AC adopt CAPWAP Tunnel to achieve AP Centralized management and control of .

CAPWAP The function of the tunnel

1. AP And AC State maintenance between .
2. AC adopt CAPWAP Tunnel pair AP Conduct management 、 Business configuration distribution .
3. When using tunnel forwarding mode ,AP take STA The data sent through CAPWAP Tunnel implementation and AC Interaction between .

5 Workflow

6 AP Online details

FIT AP Need to complete the online process ,AC To achieve the right AP Centralized management and control of , And business distribution .
To ensure AP Be able to go online ,AC The following contents need to be configured in advance

AP The online process of includes the following steps

1. AP obtain IP Address ;（ Static or DHCP The server ）
2. AP Find out AC And build with it CAPWAP Tunnel ;
3. AP Access control ;
4. AP Version update ;
5. CAPWAP Tunnel maintenance .

AP obtain IP The way of address includes the following
Static mode ： Log in to AP Manual configuration on the equipment IP Address .
DHCP The way ： By configuring DHCP The server , send AP As DHCP Client to DHCP Server request IP Address .
Typical scheme ：

Deploy dedicated DHCP Server by AP Distribute IP Address .
Use AC Of DHCP The service is AP Distribute IP Address .
Use devices in the network , For example, the core switch is AP Distribute IP Address .

6 Data forwarding method

In general , Choose the direct forwarding method , Because it can reduce AC The pressure of the