How Wi-Fi Works

Like cell phones and FM radios, wireless routers use radio waves to receive and transmit data.

Parts of a Wi-Fi signal

Wi-Fi antennas send information via 3-dimensional electromagnetic pulses. In this example, the waves form a torus or donut shape as they expand outward from the antenna.

Here is a removed piece of the 3D signal above, with a flat cross section to better illustrate its anatomy.

Gigahertz (GHz)

Routers operate on gigahertz frequencies, meaning one billion cycles (waves) per second.

Frequency band

Most Wi-Fi uses either 2.4Ghz or 5Ghz frequency bands.

Channels

The main 2.4Ghz and 5Ghz signals are divided into sub-frequencies called channels.

Packets

Channels carry packets, or small groups of data.

Waves

Packets are made up of sets of waves. Individual waves form the smallest building blocks (bits) of data.

Wi-Fi signal in detail

2.4 GHz

2.4Ghz band uses frequencies between 2.412 and 2.484Ghz for 14 channels.

2.4Ghz band can penetrate walls and floors more effectively for more coverage, but may be overcrowded since devices like microwaves and garage door openers operate in this band, as well as many PC and mobile devices.

  • Broader coverage

  • Less expensive equipment

  • More common

Channel overlap

With 2.4 GHz band, main channels (1-14) were designed to encompass multiple sub-frequencies, causing overlap.

Channels 1, 6, and 11 are often preferred channels because they can operate simultaneously without overlap interference.

Frequency bands

Dual band router

Dual band routers can operate on 2.4GHz or 5GHz frequency bands.

5GHz

5Ghz band uses frequencies between 5.035 and 5.825 for 25 channels.

5GHz band has more available channels with less congestion overall. Packets can be split up and sent over these channels for faster transfer speeds.

However, 5GHZ band can’t penetrate solid objects as effectively since walls and floors naturally resonate at a similar frequency and cancel out the signal.

Faster transfer speeds

More available channels with less congestion

Packets

Separating data into packets allows for packet switching where the router can communicate with multiple devices on multiple channels “packet-by-packet”.

In this way devices can more efficiently share available network capacity as opposed to, for example, making all devices wait for one large file transfer to one device.

Mbps

Phase-shift keying & bits

Since wave frequency remains constant during communication, the phase (position) of individual waves is shifted. This is called phase-shift keying.

Data transfer speed is usually measured in megabits per second or Mbps, meaning a router capable of 100Mbps could send about 8.3 thousand packets per second.

Packet size

Packets generally contain around 12,000 bits or 0.012 megabits.

Movie streaming example

Streaming a movie in HD would require 5 Mbps (5 million bits per second), equal to 417 packets per second.

Most routers and devices can send and detect 8 different phases of waves (8-PSK), and each phase represents a different 3-digit binary code.

Security

The current standard for securing a wireless network uses WPA2-PSK (Wi-Fi Protected Access 2, Pre-Shared Key) and 256 bit AES (Advanced Encryption Standard).

Opening a connection

The router and device perform a “four-way handshake” to verify a secure connection and construct the encryption key for data shared over this connection.

Pre-shared key

The initial “pre-shared” key -- usually a password printed on the bottom of a new router -- is never sent over the wi-fi network.

Step 1

The router encrypts an initial message using the pre-shared key . This message contains a part of the new encryption key .

On completing steps 1 and 2, both router and device have a sufficiently complex unique key that will be used to encrypt data across the connection.

Step 2

Using the pre-shared key , the device opens the message, adds the enclosed part to its key , and responds with a new addition .

Step 3

The router sends a separate key for group communications on the network.

Step 4

The device sends confirmation for the entire process.

Encrypting data with 256 Bit AES

The state

The data that needs to be encrypted (called plaintext) is split into 128 bit chunks, and then subdivided into 16 pieces or bytes (8 bits = 1 byte) and placed in a 4x4 matrix. This matrix, as it evolves throughout the encryption process, is referred to as the state.

Decryption

Using the original key generated in the four-way handshake, the device can decrypt messages by reversing the AES process.

SubBytes

Using a table called an S-Box, each byte in the state matrix is replaced with a different byte.

ShiftRows

In the state matrix, the top row stays the same, while the second row moves moves 1 to the left, the third row 2 to the left, and the fourth row 3 to the left.

MixColumns

The state matrix is multiplied by a preset matrix, each column at a time.

AddRoundKey

A unique key is generated for each round of encryption. In this stage, the state and the specific round key are mixed together using XOR.

With 256 bit encryption, plaintext repeats these four steps fourteen times.

Ciphertext

The final text at the end of the 14 rounds is known as ciphertext and is unreadable.

Hardware

Antenna

The antenna both sends and receives radio signals by creating or receiving electromagnetic waves. Having multiple antennas can increase the speed and strength of a signal as each antenna can send a separate part of each packet simultaneously (MIMO)

Wide-area-network (WAN) port

The WAN port connects to a modem, which relays information to and from the ISP (internet service provider).

Status LEDs

Local-area-network (LAN) ports

LAN ports allow devices to be connected to the router with a wire for a “wired connection.” Wired connections don’t use waves and don’t have the same issues of interference.

Random-access memory (RAM)

Routers use RAM to temporarily hold packets until it has been sent to either the modem or a connected device. Having more RAM increases the number of channels that the router can utilize.

Read-only memory (ROM)

The ROM contains firmware, or the operating system, for the router.

Modem

Modems are used to translate information to and from the router and the ISP (internet service provider).


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