Как работает Wi-Fi: Полное объяснение технологии и протоколов

The video opens by highlighting the common thread among various modern devices—laptops, smartphones, televisions, and e-readers—which is their access to the internet, notably without any wires. The narrator reflects on how the internet transformed the world, making once sci-fi concepts like instant messaging and video calls a reality. However, the initial limitation was that internet access was tethered to cables, confining users to fixed locations.

"Получив все блага цивилизации человечество по сути стало заложниками кабелей..."
"Идя по улице, сидя в кафе на работе или в поезде мы везде хотим иметь доступ в интернет с наших мобильных устройств." 0

The breakthrough came with the idea of embedding radio transmitters into portable devices to communicate wirelessly with access points, which would distribute internet signals. This concept was realized by the early 1990s but suffered from incompatibility due to different implementations by various companies.

Key points:

• Early internet access was cable-bound, limiting mobility.
• Wireless transmission via radio waves was a natural solution.
• Initial wireless implementations were incompatible across manufacturers.
• The IEEE took responsibility to standardize wireless networking, leading to the 802.11 standard, now known as Wi-Fi.
• The term "Wi-Fi" is a marketing term, not an acronym, inspired by "Hi-Fi."

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The video explains the challenge of choosing frequencies for wireless data transmission. Since radio waves spread omnidirectionally, multiple devices transmitting simultaneously on the same frequency cause interference and data corruption.

"Если несколько устройств передают свои радиосигналы рядом друг с другом, то эти сигналы будут накладываться друг на друга и искажаться." 3:19

To avoid this, different technologies use distinct frequency bands regulated by law. Wi-Fi uses unlicensed bands at 2.4 GHz and 5 GHz, which are accessible to everyone but also crowded by other household devices like microwave ovens, causing occasional interference.

"Если например включить микроволновку рядом с работающим Wi-Fi-роутером, то интернет на некоторое время может пропасть." 3:58

The 2.4 GHz band is divided into 14 channels (usually 13 available), and if too many Wi-Fi networks operate nearby, channel congestion and collisions occur, degrading performance. Newer Wi-Fi standards have added support for the 6 GHz band to alleviate congestion.

Key points:

• Wi-Fi operates mainly on 2.4 GHz and 5 GHz unlicensed bands.
• Frequency bands are divided into channels; overlapping channels cause interference.
• Household devices can interfere with Wi-Fi signals.
• Newer standards introduce 6 GHz support for better performance.
• Channel width and frequency range directly affect signal quality and speed.

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The video shifts focus to how devices connect to the internet through Wi-Fi from a TCP/IP model perspective. Unlike wired connections where each device might have a public IP, Wi-Fi devices receive private IP addresses from the router acting as a DHCP server and gateway.

"Публичное IP выдаётся только одной точки доступа, которая теперь является посредником между нашими устройствами и интернетом." 6:46

The router performs Network Address Translation (NAT), replacing the private IP in outgoing packets with its own public IP and maintaining a translation table to route incoming responses back to the correct device.

"NAT может работать в режиме один: один или один ко многим... позволяет не только осуществлять выход в интернет множеству устройств через Wi-Fi роутер, но и решает проблему нехватки IP-адресов версии 4." 7:49

Key points:

• Wi-Fi devices get private IPs assigned by the router.
• The router acts as a DHCP server and gateway.
• NAT translates private IPs to the router’s public IP for internet communication.
• NAT modes include one-to-one and one-to-many mappings.
• NAT helps conserve IPv4 addresses by sharing one public IP among many devices.

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Diving into the data link layer, the video explains that Wi-Fi frames differ significantly from wired Ethernet frames, especially in their headers and control information. Frames are categorized into three types: data frames, control frames, and management frames.

"Кадры могут быть управляющими, служебными и кадрами данных." 9:18

Management frames handle network discovery and connection setup. For example, access points broadcast beacon frames containing their MAC address, network name (SSID), and encryption method. Devices scan passively (listening) or actively (sending probe requests) to find networks.

"После того как доступная Wi-Fi сеть найдена, к ней нужно подключиться... отправляет управляющий кадр с запросом на аутентификацию." 10:17

Authentication can be open (no password) or secured with a password. After authentication, association frames exchange parameters including supported encryption methods.

Key points:

• Wi-Fi frames include data, control, and management types.
• Management frames enable network discovery and connection setup.
• Devices scan networks passively or actively.
• Authentication and association frames establish secure connections.
• SSID and encryption info are broadcast in beacon frames.

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Since Wi-Fi transmits data over the air, encryption is essential to protect privacy. The video traces the evolution of Wi-Fi security protocols:

"Первый метод безопасности Wi-Fi имел название WEP... быстро позволило найти способ как его взломать." 11:09

WEP (Wired Equivalent Privacy) used the RC4 algorithm but was quickly found vulnerable. It was replaced by WPA (Wi-Fi Protected Access) based on the TKIP protocol, then WPA2 using AES encryption, and most recently WPA3, which offers even stronger security.

Key points:

• WEP was the original Wi-Fi encryption but is insecure.
• WPA introduced TKIP for better security.
• WPA2 uses AES encryption and is widely adopted.
• WPA3 is the latest standard, enhancing security further.
• Encryption keys are negotiated during association.

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Wireless transmission is prone to collisions and interference. The video explains how Wi-Fi devices manage this:

"У каждого радиопередатчика есть свой допустимый радиус... Если свободно, передаём данные, если занято, ждём." 12:10

However, devices may not detect each other (hidden node problem), causing collisions. To mitigate this, Wi-Fi uses acknowledgments (ACK frames) to confirm receipt. If no ACK is received within a timeout, the sender retransmits.

"Отправитель ставит таймер ожидания подтверждения... если оно не пришло, значит произошла коллизия." 12:39

Additionally, devices use randomized backoff intervals before retransmitting to reduce repeated collisions.

Key points:

• Devices sense the medium before transmitting (CSMA/CA).
• Hidden node problem can cause collisions.
• ACK frames confirm successful reception.
• Retransmissions occur if ACK is missing.
• Random backoff intervals help avoid repeated collisions.

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The video breaks down the Wi-Fi frame header fields, which are more complex than Ethernet due to the wireless environment and the presence of access points.

"В заголовке целых четыре поля отведены под MAC-адреса... отправитель, получатель, точка доступа и промежуточные устройства." 14:14

Four MAC address fields accommodate scenarios involving multiple wireless networks and bridging. The frame control field (16 bits) encodes frame type (data, control, management), subtype, direction, fragmentation info, retry flags, power management, and encryption status.

"Поле управления кадром состоит из 16 бит, разделённых на 11 полей." 15:24

Fragmentation is important because wireless frames are more error-prone; smaller fragments reduce retransmission overhead. Power management flags allow devices to enter sleep mode, with access points buffering frames until the device wakes.

"Если устройство переходит в спящий режим, точка доступа записывает кадры в буфер." 17:00

The duration field reserves the medium for the frame transmission and acknowledgment, helping avoid collisions.

Key points:

• Wi-Fi frames have four MAC address fields for complex routing.
• Frame control field encodes type, subtype, direction, fragmentation, retry, power management, and encryption.
• Fragmentation reduces error impact on large frames.
• Power management allows devices to sleep and buffer frames.
• Duration field reserves channel time to prevent collisions.

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The video closes by emphasizing that Wi-Fi technology continues to evolve, but understanding these foundational concepts makes it easier to grasp new developments.

"Понимание базы и общей сути технологии позволяет без проблем самостоятельно с ней разобраться в любое время." 18:26

The creator encourages viewers to subscribe to the Telegram channel for updates and new content.

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This detailed breakdown captures the video’s narrative style, technical depth, and practical explanations, providing a thorough understanding of how Wi-Fi works from physical frequencies to frame structure and security.