Basics of WiFi
Wavy, invisible and fast!
WiFi is a wireless medium meant to transmit information based on the IEEE 802.11 standard it uses IEEE 802 standard and is thus created to work along with Ethernet.
WiFi uses an electromagnetic wave to transmit the information on different frequencies. Those frequencies are 2.4GHz and 5GHz with 6GHz coming soon for the consumer market (WiFi 6E).
Whenever you connect to a WiFi network the access point will ‘challenge’ the client that tries to connect with a password (if the network isn’t open and you should always try not to!) If the challenge is succesful. Your client is granted access and is able to connect.
History
WiFi has a long history. It started all the way back in 1997 with 802.11, soon followed with 802.11a in 1999.
Today, we’re on 802.11ac and 802.11ax since 2014 and 2019 and who knows what will follow, 6GHz WiFi is just around the corner with even greater speeds!
To the right you can see different generations of WiFi:
| Generation | IEEE name | Year | Freq. | Bandwidth | Maximum rate |
|---|---|---|---|---|---|
|
2 |
802.11a |
1999 |
5 GHz |
20 MHz |
54 mbps |
|
1 |
802.11b |
1999 |
2,4 GHz |
20 MHz |
11 mbps |
|
3 |
802.11g |
2003 |
2,4 GHz |
20 MHz |
54 mbps |
|
4 |
802.11n |
2009 |
2,4 GHz / 5 GHz |
20 MHz / 40 MHz |
600 mbps |
|
5 |
802.11ac |
2014 |
5 GHz |
20 MHz to 160 MHz |
6,77 gbps |
|
6 |
802.11ax |
2019 |
2,4 GHz / 5 GHz |
20 MHz to 160 MHz |
9,6 gbps |
Each generation came with their own respective additions on making WiFi simply better. As well as this, there are many other 802.11 variations that added new helpful features and security to the mix.
Some examples would be:
802.11w (Management frame protection) – This feature allows the protection of the management frames broadcasted by the access point for authentication/deauthentication for instance. In here lies the security addition. Someone could more easily deauthenticate you from the WiFi and then have you connect to the same WiFi network again only broadcasted by the attacker to scan all your traffic as an example. This example would be called the evil twin attack.
802.11r (Fast BBS transition) – This feature is meant for faster roaming from access point to access point by having the client pre-authenticate with other access points nearby, in simple terms. It is basically makes the client connect to other access points at the same time, but it’s not allowed to pass any frames, thus data over.
Is this explanation fully correct? No, but it’s the most easy way to grasp this without any pre-knowledge.
Access Points (APs)
As the name implies. An access point is the device that allows to access the rest of the network wirelessly. The access point itself though does not broadcast the wireless signal all by itself, it’ll use antennas for that. There are access point with external antennas that are supposed to be screwed on, meaning you can use whatever antenna. More about that later in this page.
The access point is the working brain of the whole device. It is responsible for the control plane and data plane. So, think of authentication, switching data because in a rough sense, an access point is basically a wireless switch.
Wireless signal strengt and interference
We all know the pain of having no wireless signal. Or, having a signal with tremendously low speeds. ‘How can I have four bars with no speed and high latency?’.
Well, a wireless signal goes two ways. For one, your device needs to hear the access point properly. But the access point in its turn also needs to hear your device(s) clearly too.
If there’s a wall in between you and the access point the signal can already be halved depending on the material the wall is made of.
Signal strength on a device is measured by the client device as RSSI (Received Signal Strength Indicator). This is measured in negative dBm meaning that the lower the number the stronger the connection as you’d always like to have it as close to zero as possible.
If your RSSI is higher this means you can only achieve lower speeds as the transmission size of data is lowered to decrease errors and thus retransmissions of the wireless traffic.
Interference is typically known as ‘noise’. Lower is better as this means that the access point and client device can more clearly hear each other.
Look at this as if you would be at a large party whilst trying to have a conversation with someone. If everyone starts to talk loudly you won’t be able to hear each other clearly anymore. Thus, a higher noise in the background.
Well known devices that create noise are:
- Microwaves
- Baby monitors
- DECT phones
- Wireless car keys
- Bluetooth
- Weather radar (when using DFS channels)
Antenna's and donuts
An antenna is meant for get more ‘gain’ on the signal you’re sending out. Gain is a term used for…
There are many various antenna’s for various purposes in the world of WiFi. Some are meant for short distance and a lot of clients whilst others are meant for long distance point to point connections.
Dish antenna – Typically used for point to point (one-to-one) connections as these provide very long range connections in a very tight cone in front of the antenna dish.
Yagi antenna – Similar to dish antennas but with a wider cone and shorter range. These can be used for multiple clients. These are often use for a very tight and long corridors in buildings. You can see these used for sending out a signal to a row of seats a sports stadium. For most applications an patch antenna is better suited though.
Patch antenna – Similar application as the Yagi antenna. But with a shorter range and even wider cone. You can see these often in an aisle of a super market or distribution center, for instance. But, these can just as well be used in a sport stadium like a Yagi antenna.
Whip antenna – The well known antenna’s that you see on typical consumer routers. These provide a more donut shaped radio pattern and are for that reason ideal to use when clients can come from any direction.
Omnidirectional antenna – An type of antenna that is suitable in most orientations as these send out their signal in a mostly sphere shaped form.
Each antenna propagates differently as you can read above. But how do you know if the antenna has the right propagation for your setup? The reputable manufacturers got you covered for that too as they also do provide you with special charts to get an overview of that.
Such charts can look like the image on the left.
The top two show for 2.4GHz and the bottom two for 5GHz.
The azimuth is from the perspective as if you’d look straight up at the ceiling.
The Elevation is seen as if you’d view the access point from the side.
Now imagine these circles overlapping and forming a 3D sphere. You can now imagine that it can sort of form a donut.
Access points come in many shapes, sizes and places.
Access points can be in various shapes, sizes and locations. From outdoor models being intimidatingly big too the cutest smallest access points that can be placed on a table or wall socket.
Under here are some photos to give you examples and to give you an good idea what to look out for if you would ever be somewhere in a public building or at your own work/school!
External sources and materials
Is this everything? No! The world of WiFi is really complex, broad and I simply cannot cover everything here. I only hoped ot have sparked some interest into investigating more about this. Right below, you can find many other sources to learn more about WiFi and wireless signals.
Building Secure and Robust Wireless Networks course on YouTube by Extreme Networks