What Is WLAN? Understanding Wireless Local Area Networks

① PAN: Personal Area Network (Range: 5 to 10m)

• Common wireless connection representatives include: BT (Bluetooth), NFC, Infrared.

• Wired connections: USB or other connection methods.

• Usage: Can be used for transferring small files or data, such as photos, music, etc.

② WLAN: Wireless Local Area Network (Range: Less than 100m)

• Uses wireless connections instead of wired connections for communication, expanding Ethernet and enriching device connection methods.

• A wireless local area network must have at least two devices using wireless connections to establish a communication channel.

• Typically, a wireless local area network consists of one router and one or more wireless devices that can connect to the router.

③ MAN: Metropolitan Area Network (Range: Greater than 100m)

• It is a network that spans multiple buildings across a city or town.

• A metropolitan area network is a high-speed network that can share data and resources in a city.

④ WAN: Wide Area Network (Range: Greater than 1Km)

• WAN is the largest type of network, which can include multiple LANs, CANs, and MANs.

• It is a network that spans a large geographical area, such as a country, continent, or even the entire Earth; a good example of a wide area network is the Internet.

⑤ LAN: Local Area Network

• Usually consists of a group of devices, such as personal computers, servers, or other network devices.

• The most common type of local area network is Ethernet, where two or more personal computers are connected to a router or switch via cables for data transmission between devices.

⑥ CAN: Campus Area Network

Typically, a campus area network connects two or more local area networks.

⑦ SAN: Storage Area Network

SAN is a specialized high-speed network that stores large amounts of data and provides access to them.

The operation of WLAN is built upon wired networks, expanding wired networks and changing the terminal access and interconnection methods. The basic protocols of Ethernet such as ICMP, DHCP, ARP, TCP, etc., as well as data forwarding rules, are also followed in WLAN networks without difference.

In addition to the differences in the physical layer and data link layer between LAN and WLAN, all other protocols follow the same network protocol rules as Ethernet.

LAN primarily uses the 802.3 protocol.

WLAN mainly consists of stations (Station, STA), access points (Access Point, AP), wireless media (Wireless Medium, WM), and distribution systems (Distribution System, DS).

As shown in the figure above, with the continuous updates and developments of the 802.11 protocol, the most obvious improvement is the continuous increase in Wi-Fi communication rates, and the security protocols are also constantly updated to be more secure, providing users with greater peace of mind.

Note: 5G Wi-Fi has a high frequency, thus the energy of the electromagnetic waves is strong, and the penetration capability (without changing direction) is strong, so the signal penetration will lose a lot of energy, resulting in significant attenuation during propagation and a shorter propagation distance.

Data Transmission Medium: Electromagnetic waves (carrier; propagation speed is the speed of light).

Radio Frequency Bands Used by Wireless Networks: 2.4GHz/5.8GHz.

Channel: The channel for data transmission in wireless networks, a concept in the frequency domain.

Each channel identifies a certain frequency range, with each channel having a center frequency and a certain bandwidth. Channels are public resources and cannot be changed.

Overlapping channels will cause interference, and the waveform will become higher. Each channel has a center frequency and a certain bandwidth; channel 14 is only supported in Japan.

The effective width of each channel is 20MHz, plus 2MHz of mandatory isolation bandwidth (similar to a median strip on a highway). For example, for channel 1 with a center frequency of 2412 MHz, its frequency range is 2401~2423MHz, excluding the three non-interfering channels 1, 6, and 11; there are also three groups of non-interfering channels: 2, 7, 12; 3, 8, 13; 4, 9, 14.

Note: When laying out a 2.4GHz wireless network, try to set adjacent router channels to independent channels or social channels to avoid interference between channels.

The above figure shows some of the 5GHz channels open in China. We can see that the number of non-overlapping channels in the 5GHz band is greater than that in the 2.4GHz band, reducing the probability of overlap or congestion.

The following is the division of some 5GHz channels in the United States:

When deploying APs or routers, the principle of channel selection is to use independent channels as much as possible. For APs or routers that are physically adjacent, try to choose different independent channels to reduce interference between channels. As shown in the figure below (each hexagon represents a router or AP):

Signal strength identification method: Power and decibels.

dB is used to measure the ratio of the measured power to a reference power. Its value equals the logarithm (base 10) of the ratio of the measured power to the reference power, multiplied by 10. When the reference power is taken as 1mW, this dB value is expressed as dBm, measuring power (dB)=10 * lg(measured power mW).

For example, if the power of an indoor AP is 100mW, the maximum signal strength is 20dBm=10*lg^100.

As shown in the figure, when a wireless signal passes through an obstacle, the waveform of the wireless signal changes, meaning that the wireless signal is attenuated. The attenuation degree varies depending on the material of the obstacle, with metal and concrete having the most significant impact.

Below is an analysis of the attenuation degree caused by different obstacle materials:

As shown in the figure, when there are multiple paths between the starting point and the endpoint of the signal transmission process, multipath propagation occurs. This is because some signals reach the endpoint directly, while others are reflected by obstacles to reach the endpoint, resulting in some signals being delayed and taking a longer path to reach the endpoint, causing phase changes. The signals traveling through different paths will combine at the receiver, resulting in multipath distortion.

• Different network systems overlap and generate signal interference and channel interference.
• Devices within the same network system interfere with each other at the same frequency and adjacent frequencies.
• Other devices that work on the same channel as WLAN devices interfere.

SSID: Service Set Identifier, which is the “name” or hotspot name of the wireless network we see.

BSS: Basic Service Set, identified by the AP MAC address, i.e., BSSID.

ESS (Extended Service Set) is a virtual BSS distinguished by multiple BSSs using the same SSID.

Virtual interfaces, with 16 per frequency band; APs can support multiple SSIDs.

A physical AP can virtualize 16 virtual APs.

Actual scenarios of ESSID and BSSID.

It is possible to find SSIDs that are the same but have multiple BSSIDs.

Source: 5G Communication

Reviewed by: Zhao Lixin