May 14, 2019 at 13:19Improving the work of Wi-Fi. General principles and useful things
Everyone who collected, bought, or at least tuned in a radio receiver, probably heard words such as: sensitivity and selectivity (selectivity).
Sensitivity - this parameter shows how well your receiver can receive a signal even in the most remote areas.
And selectivity, in turn, shows how well the receiver can tune to a particular frequency without the influence of other frequencies. These "other frequencies", that is, not related to signal transmission from the selected radio station, in this case play the role of radio interference.
By increasing the transmitter power, we force receivers with low sensitivity to receive our signal at all costs. An important role is played by the mutual influence of the signals from various radio stations on each other, which complicates the tuning, reducing the quality of radio communications.
In a Wi-Fi environment, radio is used as a medium for data transfer. Therefore, many of the things that were used by radio engineers and radio enthusiasts of the past and even the century before last are still relevant today.
But something has changed. The analogue format was replaced by digital broadcasting, which entailed a change in the nature of the transmitted signal.
The following is a description of common factors that affect the operation of Wi-Fi wireless networks within the framework of IEEE 802.11b / g / n standards.
Some nuances of Wi-Fi networks
For on-air broadcasting far from large settlements, when you can only receive a local FM radio station and Mayak in your VHF band on your receiver, the question of mutual influence does not arise.
Another thing is Wi-Fi devices that work in only two limited bands: 2.4 and 5 GHz. Below are a few problems that you have to know, if not overcome, how to get around.
The first problem is that different standards work with different ranges.
In the 2.4 GHz band, devices that support 802.11b / g / n work; in the 5 GHz band - 802.11a and 802.11n.
As you can see, only 802.11n devices can work both in the 2.4 GHz band and in the 5 GHz band. In other cases, we must either support broadcasting in both bands, or put up with the fact that some clients will not be able to connect to our network.
The second problem is that Wi-Fi devices operating in the radius of the next action can use the same frequency range.
For devices operating in the 2.4 GHz frequency band, 13 wireless channels with a width of 20 MHz for the 802.11b / g / n standard or 40 MHz for the 802.11n standard with 5 MHz intervals are available and approved for use in Russia.
Therefore, any wireless device (client or access point) interferes with adjacent channels. Another thing is that the transmitter power of a client device, for example, a smartphone, is much lower than that of a regular access point. Therefore, throughout the article we will talk only about the mutual influence of access points on each other.
The most popular channel that is offered by default to customers is 6. But do not flatter yourself that by choosing the next digit, we will get rid of spurious influence. An access point operating on channel 6 gives strong interference to channels 5 and 7 and weaker interference to channels 4 and 8. With an increase in the gaps between the channels, their mutual influence decreases. Therefore, to minimize mutual interference, it is highly desirable that their carrier frequencies are spaced 25 MHz apart (5 channel intervals).
The trouble is that of all the channels with little influence on each other, only 3 are available: these are 1, 6 and 11.
One has to look for some way to circumvent the existing restrictions. For example, the mutual influence of devices can be compensated by a decrease in power.
The benefits of moderation throughout
As mentioned above, reducing power is not always a bad thing. Moreover, with increasing power, the reception quality can deteriorate significantly and the point here is not at all the “weakness” of the access point. Below we will consider in what cases this may come in handy.
Radio download
The effect of congestion can be seen firsthand when you select a device to connect to. If the list of Wi-Fi networks contains more than three or four items - you can already talk about downloading radio. Moreover, each network is a source of interference for its neighbors. And interference affects network performance because it dramatically increases the noise level and this leads to the need for constant re-sending packets. In this case, the main recommendation is to lower the transmitter power at the access point, ideally, to persuade all neighbors to do the same so as not to interfere with each other.
The situation resembles a school class in a lesson when a teacher absented. Each student begins to talk with a schoolmate and other classmates. In general noise, they hear each other poorly and begin to speak louder, then even louder and eventually begin to scream. The teacher quickly runs into the classroom, takes some disciplinary measures and the normal situation is restored. If in the role of a teacher we represent the network administrator, and in the role of schoolchildren - the owners of access points, we get an almost direct analogy.
Asymmetric connection
As mentioned earlier, the transmitter power of the access point is usually 2-3 times stronger than on client mobile devices: tablets, smartphones, laptops, and so on. Therefore, the appearance of “gray zones” is very likely, where the client will receive a good stable signal from the access point, and transmission from the client to the point will work “not very”. Such a connection is called asymmetric.
In order to maintain a stable connection with good quality, it is highly desirable that there is a symmetrical connection between the client device and the access point when the reception and transmission in both directions work quite efficiently.
Figure 1. Asymmetric connection on the example of an apartment plan.
To avoid asymmetric connections, you should avoid rashly increasing the transmitter power.
When power boost is required
The factors listed below require increased power to maintain a stable connection.
Interference from other types of radio devices and other electronics
Bluetooth devices, such as headphones, wireless keyboards and mice, operating in the 2.4 GHz frequency range and affecting the operation of the access point and other Wi-Fi devices.
The devices listed below can also have a negative effect on signal quality:
- microwave microwave ovens;
- baby monitors;
- CRT monitors, wireless speakers, cordless phones, and other wireless devices;
- external voltage sources, such as power lines and power substations,
- electric motors;
- cables with insufficient shielding, as well as coaxial cable and connectors used with some types of satellite dishes.
Long distances between Wi-Fi devices
Any radio devices have a limited range. In addition to the design features of the wireless device, the maximum reach can be reduced by external factors such as the presence of obstacles, radio interference, and so on.
All this leads to the formation of local “inaccessible zones”, where the signal from the access point “does not reach” to the client device.
Signal obstruction
Various obstacles (walls, ceilings, furniture, metal doors, etc.) located between Wi-Fi devices can reflect or absorb radio signals, which leads to a deterioration or complete loss of communication.
Simple and understandable things like reinforced concrete walls, sheet metal coatings, steel frames, and even mirrors and tinted windows noticeably reduce the signal intensity.
Interesting fact : the human body attenuates the signal by about 3 dB.
The table below shows the loss of Wi-Fi signal efficiency when passing through various environments for a 2.4 GHz network.
* Effective distance - indicates the amount of decrease in radius of action after passing the corresponding obstacle compared to open space.
To summarize the interim results
As mentioned above, high signal strength alone does not improve Wi-Fi connection quality, but may interfere with good communication.
At the same time, there are situations when it is necessary to provide higher power for stable transmission and reception of Wi-Fi radio signals.
These are the conflicting requirements.
Useful features from Zyxel that may help.
Obviously, you need to use some interesting functions that will help you get out of this controversial situation.
IMPORTANT ! You can learn about the many nuances in building wireless networks, as well as about the capabilities and practical use of equipment at specialized Zyxel - ZCNE courses. Find out about the upcoming courses here .
Client steering
As noted earlier, the described problems mainly affect the 2.4 GHz band.
Happy owners of modern devices can use the 5 GHz frequency range.
Benefits:
- more channels, so it’s easier to choose those that will influence each other to a minimum;
- other devices, such as Bluetooth, do not use this range;
- Support for channels with a width of 20/40/80 MHz.
Disadvantages:
- A radio signal in this range passes through obstacles worse. Therefore, it is desirable to have not one “super-breakdown", but two or three access points with a more modest signal strength in different rooms. On the other hand, this will give a more even coverage than catching a signal from one, but “super-strong” one.
However, in practice, as always, nuances arise. For example, some devices, operating systems and software by default still offer a "good old" 2.4 GHz band for connection. This is done to reduce compatibility problems and simplify the network connection algorithm. If the connection occurs automatically or the user does not have time to notice this fact - the possibility of using the 5 GHz band will remain on the sidelines.
The Client Steering function, which by default offers client devices to immediately connect at 5 GHz, will help to change this circumstance. If this range is not supported by the client, he will still be able to use 2.4 GHz.
This function is available:
- at Nebula and NebulaFlex access points;
- in the NXC2500 and NXC5500 wireless network controllers;
- in firewalls with controller function.
Auto healing
Above were many arguments in favor of flexible power control. However, a reasonable question remains: how can this be done?
For this, Zyxel wireless controllers have a special feature: Auto Healing.
The controller with its help checks the status and performance of access points. If it turns out that one of these accesses does not work, then the neighbors will be instructed to increase the signal power in order to fill the formed silence zone. After the missing access point is back in operation, neighboring points are instructed to reduce the signal strength so as not to interfere with each other's work.
This feature is also part of a special line of wireless network controllers: the NXC2500 and NXC5500.
Secure Wireless Network Edge
Neighboring access points from a parallel network create not only interference, but can also be used as a springboard for attacks on the network.
In turn, the wireless controller must deal with this. The NXC2500 and NXC5500 controllers have plenty of tools, such as standard WPA / WPA2-Enterprise authentication, various Extensible Authentication Protocol (EAP) implementations, and a built-in firewall.
Thus, the controller not only finds unauthorized access points, but also blocks suspicious actions on the corporate network, which are most likely to carry a malicious intent.
Rogue AP Detection Function (Rogue AP Containment)
First, let's figure out what Rogue AP is.
Rogue APs are foreign access points that are not controlled by the network administrator. However, they are within reach of the enterprise’s Wi-Fi network. For example, it can be personal access points for employees that are connected without permission to the network sockets of the office. This type of initiative is bad for network security.
In fact, such devices form a channel for third-party connection to the enterprise network, bypassing the main security system.
For example, a foreign access point (RG) of access is not formally located in the enterprise network, but a wireless network has been created on it with the same SSID name as on legal access points. As a result, the RG point can be used to intercept passwords and other secret information when corporate network clients mistakenly try to connect to it and try to transfer their credentials. As a result, the user credentials will be known to the owner of the phishing point.
Most Zyxel access points have a built-in radio airborne scan feature to detect rogue points.
IMPORTANT ! Detection of foreign points (AP Detection) will only work if at least one of these “watchdog” access points is configured to work in network monitoring mode.
After the Zyxel access point, in the monitoring mode, detects foreign points, a blocking procedure can be undertaken.
Let's say Rogue AP emulates a legal access point. As mentioned above, an attacker can duplicate corporate SSID settings on a false point. Then the Zyxel access point will try to prevent dangerous activity, introducing interference through the broadcast broadcast of dummy packets. This will make it impossible for clients to connect to Rogue AP and intercept their credentials. And the "spy" access point will not be able to fulfill its mission.
As you can see, the mutual influence of access points not only introduces annoying interference when working with each other, but can also be used to protect against attackers.
Conclusion
The material in the framework of a small article does not allow us to talk about all the nuances. But even with a quick review, it becomes clear that the development and maintenance of a wireless network has quite interesting nuances. On the one hand, it is necessary to combat the mutual influence of signal sources, including by reducing the power of access points. On the other hand, it is necessary to maintain the signal level at a sufficiently high level for stable communication.
You can get around this contradiction by using the special functions of the wireless network controllers.
It is also worth noting the fact that Zyxel is working on improving everything that helps to achieve high-quality communication without resorting to high costs.