Everyone who collected, bought, or at least tuned a radio receiver probably heard such words as: sensitivity and selectivity (selectivity).
Sensitivity - this parameter indicates 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 the transmission of a signal from the selected radio station, in this case play the role of radio interference.
By increasing the power of the transmitter, we force receivers with low sensitivity to receive our signal at all costs. An important role is played by the mutual influence of signals from different radio stations on each other, which complicates the setting, reducing the quality of radio communication.
The Wi-Fi environment uses radio air as a medium for data transmission. Therefore, many things operated by radio engineers and radio amateurs of the past and even the century before last are still relevant today.
But something has changed. For changing analog digital broadcasting came to the format, which led to a change in the nature of the transmitted signal.
The following is a description of common factors that affect the operation of wireless Wi-Fi networks within the 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 the signal of a local FM radio station and also Mayak in the VHF band on your receiver, the question of mutual influence does not arise.
Another thing is Wi-Fi devices that operate only in two limited bands: 2,4 and 5 GHz. Below are a few problems that you have to, if not overcome, then know how to get around.
The first problem β different standards work with different ranges.
In the 2.4 GHz band, devices that support the 802.11b / g standard work, and 802.11n standard networks, in the 5 GHz band, devices of the 802.11a and 802.11n standard work.
As you can see, only 802.11n devices can operate 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 - Wi-Fi devices operating in the vicinity may use the same frequency band.
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 allowed for use in Russia.
Therefore, any wireless device (client or access point) interferes with adjacent channels. Another thing is that the transmitter power of the client device, for example, a smartphone, is much lower than that of the most ordinary access point. Therefore, throughout the article, we will only talk 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 number, we will get rid of parasitic influence. An access point operating on channel 6 gives strong interference to channels 5 and 7 and weaker interference to channels 4 and 8. As the gaps between channels increase, their mutual influence decreases. Therefore, in order to minimize mutual interference, it is highly desirable that their carrier frequencies be 25 MHz apart (5 inter-channel intervals).
The trouble is that of all the channels with little influence on each other, only 3 channels are available: these are 1, 6 and 11.
We have to look for some way to get around the existing restrictions. For example, the mutual influence of devices can be compensated by reducing the power.
About the benefits of moderation in everything
As mentioned above, power reduction is not always a bad thing. Moreover, with an increase in power, the reception quality can deteriorate significantly, and the point here is not at all the βweaknessβ of the access point. Below we will consider in what cases it can be useful.
Radio download
The effect of congestion can be seen with your own eyes, at the moment of choosing a device to connect. If there are more than three or four items in the Wi-Fi networks selection list, we can already talk about downloading the radio. In addition, 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 of 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 is reminiscent of a school class in a lesson when the teacher was away. Each student begins to talk with a neighbor on the desk and other classmates. In the general noise, they do not hear each other well and start talking louder, then even louder and eventually start screaming. The teacher quickly runs into the classroom, takes some disciplinary action, and the normal situation is restored. If we imagine the network administrator as a teacher, and the owners of access points as schoolchildren, we get an almost direct analogy.
Asymmetrical 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, it is very likely that βgray zonesβ will appear, where the client will receive a good stable signal from the access point, and the transmission from the client to the point will not work very well. Such a connection is called asymmetric.
To maintain a stable connection with good quality, it is highly desirable that there be a symmetrical connection between the client device and the access point, when reception and transmission in both directions work efficiently enough.
Figure 1. Asymmetric connection on the example of an apartment plan.
Inadvertently increasing transmitter power should be avoided to avoid asymmetrical connections.
When Power Up is Needed
The following factors require more power in order to maintain a stable connection.
Interference from other types of radio communication devices and other electronics
Bluetooth devices such as headphones, wireless keyboards and mice that operate in the 2.4 GHz band and interfere with the hotspot and other Wi-Fi devices.
The following devices can also have a negative impact on signal quality:
- microwave ovens;
- baby monitors;
- CRT monitors, wireless speakers, cordless phones and other wireless devices;
- external sources of electrical voltage, 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 distance may be reduced by external factors such as obstacles, radio interference, and so on.
All this leads to the formation of local βinaccessible zonesβ, where the signal from the access point βdoes not reachβ the client device.
Signal Obstacles
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.
Things as simple and straightforward as reinforced concrete walls, sheet metal cladding, steel framing, and even mirrors and tinted glass will noticeably reduce signal strength.
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 reduction in the range after passing the corresponding obstacle compared to open space.
Let's sum up the intermediate results
As mentioned above, high signal strength by itself does not improve the quality of Wi-Fi communication, but it can interfere with establishing a good connection.
At the same time, there are situations when it is necessary to provide higher power for stable transmission and reception of the Wi-Fi radio signal.
These are conflicting claims.
Useful features from Zyxel that can help
Obviously, you need to use some interesting features that will help get out of this contradictory situation.
IMPORTANT! You can learn about the many nuances in building wireless networks, as well as the possibilities and practical use of equipment at specialized Zyxel-ZCNE courses. Find out about upcoming courses .
Client Steering
As noted earlier, the described problems mainly affect the 2.4GHz band.
Happy owners of modern devices can use the 5GHz frequency range.
Advantages:
- more channels, so it's easier to choose those that will affect each other to a minimum;
- other devices such as Bluetooth do not use this range;
- support for 20/40/80 MHz channels.
Disadvantages:
- the radio signal in this range passes through obstacles worse. Therefore, it is desirable to have not one "super-penetrative", 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 picking up a signal from one, but "super-strong".
However, in practice, as always, there are nuances. For example, some devices, operating systems and software still offer the "good old" 2.4GHz band for connection by default. This is done to reduce compatibility issues and simplify the network connection algorithm. If the connection occurs automatically or the user did not have time to notice this fact, the possibility of using the 5GHz band will remain on the sidelines.
The Client Steering function will help to change this circumstance, which by default prompts client devices to immediately connect via 5GHz. If this range is not supported by the client, it will still be able to use 2.4GHz.
This feature is available:
- in Nebula and NebulaFlex access points;
- in NXC2500 and NXC5500 wireless network controllers;
- in firewalls with controller function.
Auto Healing
Many arguments have been made above in favor of flexible power control. However, a reasonable question remains: how to do this?
Zyxel wireless controllers have a special feature for this: Auto Healing.
The controller with its help checks the status and performance of access points. If it turns out that one of the access points is not working, then the neighboring ones will be instructed to increase the signal strength in order to fill the resulting zone of silence. After the missing access point is back online, neighboring access points are instructed to reduce signal strength so as not to interfere with each other's work.
This feature is also available on a dedicated line of wireless 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 to attack the network.
In turn, the wireless network controller must deal with this. The NXC2500 and NXC5500 controllers have enough tools in their arsenal, 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 activities on the corporate network, which most likely carry malicious intent.
Rogue AP Detection (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 present within the reach of the enterprise Wi-Fi network. For example, it can be personal access points of employees, included without permission in the network sockets of a work office. This kind of amateur activity is bad for the security of the network.
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) is not formally located on the enterprise network, but it has a wireless network with the same SSID name as the legitimate access points. As a result, the RG point can be used to intercept passwords and other sensitive information when clients on the corporate network mistakenly try to connect to it and try to pass their credentials. As a result, user credentials will be known to the host of the phishing point.
Most Zyxel access points have a built-in radio scanning feature to detect rogue points.
IMPORTANT! 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, when operating in monitoring mode, detects foreign points, a blocking procedure can be undertaken.
Let's say the Rogue AP mimics a legitimate access point. As mentioned above, an attacker can duplicate corporate SSID settings on a false point. The Zyxel access point will then attempt to interfere with the dangerous activity by interfering with broadcast dummy packets. This will prevent clients from connecting to the Rogue AP and intercepting 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 attacks by intruders.
Conclusion
The material within the framework of a small article does not allow to talk about all the nuances. But even with a cursory review, it becomes clear that the development and maintenance of a wireless network have quite interesting nuances. On the one hand, it is necessary to deal with the mutual influence of signal sources, including by reducing the power of access points. On the other hand, it is necessary to keep the signal level high enough for stable communication.
You can get around this contradiction by using special functions of wireless network controllers.
Also worth noting is the fact that Zyxel is working on improving everything that helps to achieve high-quality communication without resorting to high costs.
Sources of
Source: habr.com