Popularization of wireless knowledge: the difference between "thin" AP and "fat" AP, just read this article!

1. Basic concepts of AP

Wireless AP (Access Point): that is, wireless access point, which is used for the wireless switch of the wireless network and is also the core of the wireless network. The function is to compile the wired signal (that is, the electrical signal) transmitted through the twisted pair in the local area network, convert it into a radio signal and transmit it to wireless terminals such as computers and mobile phones, and at the same time convert the wireless signals sent by these wireless terminals into wired signals. Signals are transmitted within the LAN via twisted pair wires. Wireless AP is the access point for mobile computer users to enter the wired network. It is mainly used in broadband homes, buildings and parks, and can cover tens of meters to hundreds of meters. Wireless AP (also known as session point or access bridge) is a very broad name, which includes not only simple wireless access points (in this way, forming wireless coverage, that is, wireless local area network. We usually say AP, both It refers to the thin AP below.

In a wireless network, an AP is equivalent to a hub of a wired network. It can connect various wireless clients. The network card used by the wireless client is a wireless network card, and the transmission medium is air (electromagnetic waves). Logically, it is the central point of a wireless unit through which all wireless signals in the unit can be exchanged. AP is an essential device in the basic mode of wireless local area network. Although only using wireless network card without using AP can form a wireless local area network in point-to-point mode, but such wireless local area network is somewhat special, it is only suitable for temporary wireless connection . After using the AP, you can not only get permanent wireless connection service, but also can centrally manage users and greatly improve the security of the wireless network. In layman's terms, a wireless AP is a communication bridge between a wireless network and a wired network. Since the coverage of the wireless AP is a circular area that spreads outward, the wireless AP should be placed in the center of the wireless network as much as possible, and the straight-line distance between each wireless client and the wireless AP should not exceed 30m to avoid Communication failure due to excessive attenuation of the communication signal.

2. The difference between wireless AP and wireless router

With the rapid development of wireless networks, building a small wireless LAN has become the preferred networking solution for SOHO and home users. However, just as many people easily confuse wireless network cards and wireless network cards, many users also cannot distinguish between wireless APs and wireless routers. Many users found that wireless APs and wireless routers can realize wireless Internet access when they inquired about information before purchasing products, but when they bought back relatively cheap wireless APs and started to build a wireless network, they found that wireless APs cannot be used together with ADSL, which is completely impossible. Wifi.

Wireless AP, simply speaking, is a wireless switch in a wireless network. It is the access point for mobile terminal users to enter the wired network. It is mainly used for home broadband and enterprise internal network deployment. The wireless coverage distance is tens of meters to hundreds of meters. The main technology is 802.11X series. General wireless APs also have an access point client mode, which means that wireless links can be performed between APs, thereby expanding the coverage of the wireless network.

Since the simple AP lacks the routing function, it is equivalent to a wireless switch and only provides a function of wireless signal transmission. Its working principle is to transmit the network signal through the twisted pair, and after compiling by the wireless AP, convert the electrical signal into a radio signal and send it out to form the coverage of the wireless network. Depending on the power, the network coverage is also different. Generally, the maximum coverage distance of a wireless AP can reach 400 meters.

The extended AP is what we often call a wireless router. A wireless router, as its name implies, is a router with a wireless coverage function, which is mainly used for users to surf the Internet and wireless coverage. Through the routing function, the Internet connection sharing in the home wireless network can be realized, and the wireless shared access of ADSL and community broadband can also be realized. It is worth mentioning that wireless and wired terminals can be assigned to a subnet through a wireless router, so that various devices in the subnet can exchange data conveniently.

For extended APs, they can be interconnected within a short distance; if the transmission distance is relatively long, then equipment such as wireless bridges and special antennas are needed to help.

From the appearance point of view, the two are basically similar in length, and it is really difficult to distinguish them. But I believe careful users have already seen the difference between the two, by the way, that is, their interfaces are different. A simple wireless AP usually has a wired RJ45 network port, a power port, a configuration port (USB port or configuration through the WEB interface), and fewer indicator lights; while a wireless router has four more wired network ports, except for one The WAN port is used to connect to the upper-level network equipment, and the four LAN ports can be wired to connect to computers in the intranet, and there are naturally more indicator lights.

3. Thin AP Architecture

Wireless APs can generally be divided into fat APs (Fat APs) and thin APs (Fit APs), which are not distinguished by their appearance, but by their working principles and functions. Of course, some fat and thin APs can be distinguished in appearance. For example, the AP with a WAN port must be a fat AP.

Thin AP, the understanding of the image is to slim down the fat AP, remove the routing, DNS, DHCP server and many other loaded functions, and only keep the wireless access part. The AP we often refer to refers to this type of thin AP, which is equivalent to a wireless switch or hub, and only provides a function of wired/wireless signal conversion and wireless signal reception/transmission. As a part of the wireless LAN, the thin AP cannot work independently, and must cooperate with the management of the AC to become a complete system. The following figure is a typical thin AP planning.

Fit AP, the image to understand is a thin fat AP, remove routing, DNS, DHCP server and many other loading functions, and only keep the wireless access part. The AP we often refer to refers to such a Fit AP, which is equivalent to a wireless switch or hub, and only provides a wired/wireless signal conversion and wireless signal receiving/sending function. As a component of the WLAN, the Fit AP cannot work independently. It has to work with AC management to be a complete system.

Fit APs do not have management functions. It can be understood as a signal sending and receiving antenna. Its management functions are performed by the backend, called the wireless controller (AC).

Fit AP cannot manage itself. AC needs management. Fit AP is only responsible for broadcasting SSID and connecting terminals. Typically, ultra-small networks use Fat APs, while small networks use Fit APs.

The reason for this is mainly because of the wireless coverage of campuses deployed by large enterprises in the case of many wireless routers. It's normal to have hundreds of wireless routers, but it can be cumbersome to manage. It is impossible to use one router like a home router. To configure, all unified management of AC is more convenient and faster.

A high-end wireless controller (AC) can manage hundreds of thousands of wireless APs, and can centrally configure and deliver configurations. Enterprise-level wireless APs can actually be fat and can be edited by different software. Implemented, but meaningless in the context of large-scale deployments.

The thin AP works as follows:

After the AP is powered on, it sends a DHCP request to the DHCP server by broadcasting, with the goal of obtaining an IP address.
When the AC allocates an IP address to the AP, it also informs the AP of its own AC address.
When the AP obtains multiple AC addresses, the AP sends a join request message to the first AC address in its AC address list, and if the AC does not respond, it will try the next AC. If the AC accepts the AP, it will send back a joining response message to the AP.
The AC will compare the information reported by the AP (the manufacturer, device model, hardware version, and these three information are required). If they are different, they will send back a reply that they are not allowed to join the AC. If they are the same, they will send a reply to the AP. Return the response information (mainly including AP version and other information) for allowing to join the AC.
The AP judges whether to upgrade the version according to the response information of the AC. If not, it enters the AC configuration AP state (delivering configuration); if necessary, it enters the AP version upgrade state.
The AP establishes an unencrypted CAPWAP tunnel and an encrypted CAPWAP tunnel with the AC, the former is used to transmit the management data flow (5246), and the latter is used to transmit the data of the wireless client (5248).

Key features of Fit AP:

Fit AP is relative to Fat AP. It is an AP with only encryption and radio frequency functions. It has a single function and cannot work independently.
The entire Fit AP wireless network solution consists of ACs and Fit APs based on a wired network.
There is "zero configuration" on the Fit AP, and all configurations are centralized on the AC. This also makes the Fit AP solution more convenient for centralized management, and thus has functions that Fat APs do not have, such as Layer 3 roaming and user-based authorization.

In order to ensure that channels do not interfere with each other, large-scale wireless networks must plan and implement WLAN channels in a unified manner. WLAN channel planning needs to follow two principles, cellular coverage and channel spacing. According to the coverage density and interference situation, choose 2.4G/5G single-frequency or dual-frequency coverage. The AP alternately uses channels 1, 6, and 11 of 2.4G and channels 36, 40, and 44 of 5.0G to avoid mutual interference of signals; generally, the frequency band of 2.4G or 5.0G is used alone. In places, dual-band coverage can be enabled to provide better access capabilities.

Using thin AP, how to effectively ensure the safe transmission of user data, and how to ensure that user data is not leaked?

Since the thin AP cannot work alone and must be used in conjunction with the AC, there must be a protocol between the two to enable them to interconnect and communicate. Therefore, Cisco's big brother made a LWAPP protocol, and this protocol is the predecessor of the CAPWAP protocol!

But please note that LWAPP is privately owned by Cisco, and other manufacturers cannot use it directly, otherwise they will be sued. As a result, other manufacturers made a protocol according to their own ideas, which would be chaotic. Your entire agreement and I also agree with the entire agreement. If the thin AP and AC are the same manufacturer, it will be no problem. If it is not easy for the manufacturer, no communication

Therefore, in order to solve the incompatibility of the tunneling protocol, the AP of manufacturer A and the AC of manufacturer B cannot communicate with each other. In 2005, the IETF established the CAPWAP working group to standardize the tunneling protocol between the AP and the AC.

4. Fat AP Architecture

The so-called FAT AP refers to the self-management of the AP (Access Point), which can independently provide SSID, authentication, and DHCP functions, and can provide Internet access parameters such as IP addresses to the hosts bound to the AP, and realize the 802.11 (wireless interface) protocol and 802.3 ( Wired interface) protocol conversion, its network management interface is no different from that of an ordinary switch, and can be managed locally through the console or remotely through SSH.

In addition to the wireless access function mentioned above, the fat AP generally also has WAN and LAN ports, supports DHCP server, DNS and MAC address cloning, VPN access, firewall and other security functions. Fat AP usually has its own complete operating system, which is a network device that can work independently, and can realize functions such as dialing and routing. The example in the figure below is our typical fat AP plan.

Main features of Fat AP:

Fat AP is opposite to Fit AP. Fat AP integrates the physical layer of WLAN, user data encryption, user authentication, QoS, network management, roaming technology and other application layer functions.
Fat AP wireless network solution can be composed of Fat AP directly on the basis of wired network.
Fat APs have complex structures and are difficult to manage centrally.

5. Advantages and disadvantages of fat and thin AP networking

Fat mode is a traditional WLAN networking solution. The wireless AP itself undertakes complex functions such as authentication termination, roaming switching, and dynamic key generation. Relatively speaking, the functions of the AP are relatively heavy, so it is called a Fat AP.

The use of fat APs or thin APs mainly considers the scale of the network that needs to be deployed. Fat APs are generally used in small wireless network construction and can work independently without the cooperation of ACs. It is generally used in family, small business or small office scenarios that only need a small amount to fully cover. Thin APs are generally used in the construction of medium and large wireless networks. A certain number of thin APs and AC products are used to build a large wireless network coverage, which is convenient for management and maintenance. The usage scenarios are generally shopping malls, supermarkets, scenic spots, hotels, restaurants, entertainment, Corporate office, etc. The advantages and disadvantages of the fat AP and thin AP networking solutions are described and compared in detail in the following aspects.

1. Network scale and application scenarios

Fat APs are generally used in small-scale wireless network construction and can work independently without the cooperation of ACs. It is generally used in households, small businesses or small office scenarios that only require a small amount to fully cover.

Thin APs are generally used in the construction of medium and large wireless networks. A certain number of APs and AC products are used to build larger wireless network coverage. The usage scenarios are generally shopping malls, supermarkets, scenic spots, hotels, restaurants and entertainment, and corporate offices.

2. Wireless Roaming

Fat AP networking cannot implement wireless roaming. When a user walks from the coverage area of one fat AP to the coverage area of another fat AP, he will reconnect to a fat AP with a strong signal, re-authenticate, and obtain an IP address again, resulting in network disconnection.

When the user walks from the coverage area of one thin AP to the coverage area of another thin AP, the signal will be switched automatically, and there is no need to re-authenticate or obtain an IP address again. The network is always connected online, which is convenient to use.

3. Automatic load balancing

When many users are connected to the same fat AP, the fat AP cannot automatically perform load balancing to distribute users to other fat APs with lighter loads, so the fat APs will frequently experience network failures due to heavy loads.

In the AC+thin AP network, when many users are connected to the same thin AP, the AC will automatically assign the users to other APs with lighter loads according to the load balancing algorithm, which reduces the failure rate of the AP and improves availability of the entire network.

4. Management and maintenance

Fat APs cannot be managed centrally, and need to be configured individually one by one, and the configuration work is cumbersome. Thin APs can cooperate with AC products for centralized management without separate configuration, especially when there are a large number of APs, the advantages of centralized management are obvious.

6. Summary

Many wireless APs nowadays are no longer simply fat APs or thin APs, but a collection of fat and thin APs, such as all wireless AP series of Fengrunda, whether it is single-frequency or dual-frequency, or high-power Wireless APs are fat and thin.

Fat and thin means that it integrates the functions of "fat AP" and "thin AP". It can be used not only as a fat AP, but also as a thin AP, that is, its Fat mode and Fit mode. It must be determined according to different networking environments.

Fit mode is an emerging WLAN networking mode. Compared with the Fat mode solution, a wireless switch or wireless controller is added as a central centralized control and management device. The authentication termination, roaming switch, dynamic key, etc. that were originally carried on the Fat AP itself Complex business functions are transferred to wireless switches or wireless controllers.

Fit mode reduces the burden of a single AP and improves the work efficiency of the entire network. At the same time, due to the centralized management feature of the Fit AP solution, it is easy to expand the expansion of richer service functions by upgrading the software version of the wireless controller. All APs are installed with zero configuration, and in addition to transmitting data, they can also monitor the radio frequency environment of the entire network and detect illegal intrusion APs and illegal clients.

Generally speaking, Fat can be used alone, and each AP needs to be configured before it can be used. It is recommended for a small number of APs, but the device structure is complex and difficult to manage centrally. The Fit mode cannot be used alone, but needs to be used with the wireless controller. It is recommended to use it when there are many Fit APs. It features "zero configuration", and all configurations are concentrated on the AC. Although the AC+thin AP networking mode has many advantages mentioned above, in the case of small-scale networking, many users, such as restaurants, cafes, 4S stores, inns, beauty salons, gyms, etc., will choose to use it based on cost. Several fat APs are networked to provide WiFi for customers. The result is that although WiFi is available, the user experience is not good, and it cannot add points to its own services. In many cases, it even reduces points, making customers unwilling to patronize again.

It can be seen from the above that the networking scheme of fat AP is rarely used at present, and the networking mode of AC+AP is basically used, and the AP must be used in conjunction with the AC controller.

Based on this, the current wireless AP basically realizes the integration of fat and thin. Compared with the wireless AP of Fengrunda that I know, no matter it is in-wall type, ceiling type, single frequency or dual frequency, it supports two working modes of Fat/Fit , can be switched according to the needs of its own usage scenarios, and the networking is more flexible.