What's 802.11 exactly?
In my previous post, I gave a quick overview of the IEEE 802 standards, now we are ready to delve further into the world of 802.11 aka Wi-Fi!
802.11 is potentially the most commonly seen standard out of all the standards. It is shown on the box of every home wireless router to tell people what Wi-Fi standard they are getting, despite the majority of people not understanding what those numbers are or whether “n” is better than “g”
So, what is the 802.11 standard? Well, of course, it’s what defines Wireless LANs and is more commonly associated with Wi-Fi (yes, technically, they are two different things, but let’s not get into that).
So, going way back, we had the original 802.11 specification in 1997, though this quickly became obsolete and was replaced by 802.11b, unofficially now known as “Wi-Fi 1”in 1999.
802.11a was also released in 1999 and supported the 5Ghz frequency band, but due to the higher cost of radios and the limited distance, 802.11a was less popular than 802.11b, even though the theoretical speed was higher.
It was not until 802.11n that the Wi-Fi alliance began officially naming the 802.11 standards with friendly names like Wi-Fi 4, and Wi-Fi 5.
Each iteration of 802.11 came with newer technology, which increased the throughput, here are the footnotes:
802.11n introduces High Throughput (HT) speeds, which were accomplished through a few mechanisms:
Increasing channel width.
Using advanced 64-quadrature amplitude modulation (QAM), which in short manipulates the amplitude and phase of the signal to encode data, it’s all very scientific, and not something I have ever needed to fully understand 🙂
Techniques like Multiple Input/Multiple Output (MIMO) - I’ll get into this later.
802.11ac only operates on the 5Ghz frequency and accomplishes almost 6Gbps of theoretical throughput using methods known as Very High Throughput (VHT).
802.11ax (Wi-Fi 6) introduces Multi-User MIMO ( MU-MIMO), enabling multiple transmitters simultaneously.
Wi-Fi 6E is an extension of 802.11ax. It adds support for the 6GHz frequency and 1024-QAM techniques to theoretically support up to 7.8Gbps.
Wi-Fi 7 is new in 2024, and has some big promises, but use of this technology will take some time to move into the wider business world, mostly due to Wi-Fi 6 refreshes only just occurring.
Some Key concepts
Here are a few key concepts in the 802.11 standards that are useful to understand.
The Basic Service Set
A Basic Service Set (BSS) is a key concept of a Wi-Fi network. It refers to the group of devices (like laptops, smartphones, etc.) connected to the same access point (AP). Think of the BSS as the small "bubble" of wireless coverage provided by a single AP, and any device within that bubble can communicate with the AP and other devices in the same BSS.
There is a unique identifier of the BSS. It’s usually the MAC address of the AP, this is known as the BSSID.
While multiple APs can broadcast the same SSID (the name of the network), each AP has a unique BSSID to identify its own network coverage.
BSS operates in two main modes:
Infrastructure Mode: Where stations communicate through an AP.
Ad-Hoc Mode: Where stations communicate directly with each other without an AP.
Extended Service Set (ESS)
An Extended Service Set (ESS) is made up of multiple BSSs, usually connected through a wired network, to create a larger, unified wireless network. This is common in large-scale deployments like enterprises or campuses.
The BSSs within an ESS share the same SSID (Service Set Identifier), allowing devices to roam seamlessly between APs while maintaining a connection.
802.11 Frames
A WLAN carries a few different types of frames, which are different from an Ethernet segment.
Management Frames
Firstly we have the management frame, which as you can probably depict from the name is for managing the wireless network.
Management frames are responsible for establishing and maintaining the communication between devices on a WLAN. Some key management frames are;
Beacon Frames: Sent by access points (APs) to announce the presence of a wireless network.
Authentication/Association Frames: Handle connecting a client to the AP, including verifying credentials.
Control Frames
These frames help coordinate data transmission, ensuring smooth communication by managing access to the medium. Examples include:
Request to Send (RTS) and Clear to Send (CTS): Manage the access to the wireless medium, preventing collisions by coordinating when devices can transmit.
Data Frames
As the name suggests, these frames carry the actual payload or data from source to destination. These frames are responsible for the bulk of the communication over the WLAN.
Frame Structure
The frame structure in wireless is much more complex than in ethernet. Understanding the some of the components of these frames are important for those of you sitting exams, and if you want to specialise in wireless networking, this will become fundamental. I personally can never remember this, hence needing to write it down.
An ethernet frame ( remember frames are a layer 2 concept) contains two address fields, source and destination mac address. Here’s a picture to help visualise the frame!
Now a wireless frame has a lot more going on, the most obvious difference is the frame has four address fields
OK, why does it need four addresses! and which address is which. This is one of the functions of frame control. Inside Frame control, bits are set to flag certain functions
Protocol Version: Indicates the version of the 802.11 standard.
Type and Subtype: Identifies the type of frame (e.g., Management, Control, or Data) and its specific subtype.
To_DS and From_DS: Indicates the direction of the frame (to/from the Distribution System).
Other Flags: Include Retry, Power Management, More Fragments, etc.
The To_DS and From_DS flag are the key ones to know here, and I struggled to grasp this the first time I read about it. But I will try and explain as best I can.
Firstly some acronyms of course!
DS stands for distributed system, which refers the wired or wireless backbone that connects the Access Points and allows communication between wireless devices and wired networks. So basically the rest of the network from the perspective of the access point.
STA means station, or more simply, the wireless client.
AP is access point of course.
Setting the To_DS and From_DS bits determine the values that are entered into the address fields of the frame.
For example, a typical scenario of a wireless client sending data to a server on the wired network would result in the To_DS bit set to 1 and the From_DS bit set to 0.
An example of where neither bit is set would be when two clients are communicating directly without an AP in between.
Orthogonal Frequency Division Multiplexing
Orthogonal Frequency Division Multiplexing, or OFDM, is one of the heroes of modern Wi-Fi. It’s a modulation technique that splits a wireless channel into smaller sub-channels, each transmitting data simultaneously. This approach dramatically improves efficiency and resilience to interference.
Imagine a road with multiple lanes, and instead of forcing all the traffic onto a single lane, OFDM opens up multiple lanes, allowing data to flow more smoothly. This reduces congestion and ensures more stable connections, even in noisy environments.
OFDM first appeared in 802.11a and has been a staple in every major Wi-Fi standard. It’s one of the key reasons why Wi-Fi can support high-speed data transfers and work reliably in environments with many competing signals, like urban areas or crowded venues.
Multiple Input Multiple Output aka MIMO
MIMO was mentioned earlier in this piece, but I did not explain what it was, and that is because it deserves it’s own section.
Prior to MIMO, wireless comms used Single Input, Single Output or SISO where a single antenna was used for both transmitting and receiving, this had significant limitations on throughput, as you can imagine. Such a massive bottleneck.
MIMO (Multiple Input, Multiple Output) using multiple antennas at both the transmitter and receiver ends of the communication. This means that data streams could be sent simultaneously, maximising the throughput.
Now there was still a small limitation on that MIMO did not address, and that was that the access point could only communicate with one client device at a time. which whilst doing so very quickly, slowed things down a bit.
This was solved in Wi-Fi 5 ( or 802.11ac) with MU-MIMO or Multi-user Multiple Input, Multiple Output.
MU-MIMO does a few things to achieve this magic, but one key feature is that it splits spatial streams across devices which basically gives each device it’s own path for data transfer.
Clients no longer need to sit and wait for the last device to shut up before it can send data.
802.11r
Seamless roaming is critical for applications like video conferencing, online gaming, and VoIP calls, where even a momentary disconnect can cause noticeable interruptions. That’s where 802.11r, also known as Fast BSS Transition, really helps.
In traditional Wi-Fi networks, when your device moves from one access point to another, it has to go through the entire authentication process again, which can take several milliseconds. 802.11r speeds this up by allowing devices to pre-authenticate with neighbouring access points while still connected to the current one. The transition is nearly instantaneous when the device roams, maintaining the connection without a hiccup.
This feature is handy in environments like large campuses, stadiums, or warehouses where constant movement between access points is the norm.
But have you ever wondered how your devices know which access point to connect to whilst roaming?
You may have come across the term Radio Resource Management or RRM.
Radio Resource Management aka 802.11k
Enabled by the 802.11k standard, this feature helps devices make smarter roaming decisions by collecting information about the network’s topology, such as signal strength and load on nearby access points.
Here’s how it works: when your device connects to a network, it can request a neighbour report from the current access point. This report lists other nearby access points along with their signal strengths and channels. With this data, your device can seamlessly switch to a better access point when needed, ensuring you stay connected with minimal disruptions. It’s a must-have for environments with multiple access points, such as airports, offices, and shopping centres.
BSS Colour Tags
BSS Colour Tags, introduced as part of Wi-Fi 6, are a way for devices to distinguish between overlapping networks operating on the same channel.
Imagine this: you’re in an apartment block, and everyone’s Wi-Fi is crammed onto a handful of overlapping channels. Without BSS Colouring, your router might waste time interpreting signals from your neighbour’s network.
BSS Colour Tags assign a unique identifier (a "colour") to each Basic Service Set (BSS). This allows devices to filter out signals that belong to other networks, reducing interference and improving performance. It’s especially effective in high-density environments, like offices, apartments, or even busy cafes, where multiple networks coexist.
Fine Timing Measurement aka 802.11mc
802.11mc, or Wi-Fi Fine Timing Measurement (FTM), enhances location-based services by using precise timing to determine the distance between a device and Wi-Fi access points. This standard enables devices to measure Round Trip Time (RTT)—the time a signal travels to an access point and back.
Remember, though, that both the access point and the client device must be capable of supporting 802.11mc!
Using RTT data from multiple access points, devices can calculate their position with high accuracy, often within a meter This makes 802.11mc ideal for applications like indoor navigation, asset tracking, and location-based services.
Wireless Networking is a whole different beast to traditional wired networking, I really hope you got something useful from this article. This hopefully gave you some food for thought and the urge to go an find out more!
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