Anyone who has assembled, purchased, or even just configured a radio receiver has probably heard terms like: sensitivity and selectivity.
Sensitivity indicates how well your receiver can pick up a signal even in the most remote areas.
Selectivity, on the other hand, shows how well the receiver can tune into a specific frequency without interference from other frequencies. These 'other frequencies', which do not relate to the transmission from the selected radio station, act as radio noise in this context.
By increasing the transmitter's power, we compel receivers with low sensitivity to pick up our signal at all costs. The mutual influence of signals from various radio stations on each other plays a significant role, complicating tuning and reducing the quality of radio communication.
In a Wi-Fi environment, radio waves are used as the medium for data transmission. Therefore, many aspects that radio engineers and hobbyists dealt with in the past century, and even the century before that, remain relevant today.
However, some things have changed. The analog format has been replaced by digital broadcasting, leading to a change in the nature of the transmitted signal.
Below is a description of the common factors that impact the functioning of Wi-Fi wireless networks within the IEEE 802.11b/g/n standards.
Some nuances of Wi-Fi networks
For terrestrial radio broadcasting far from major urban areas, where you can only receive the signal from the local FM radio station and perhaps 'Mayak' in the VHF range, the issue of mutual influence does not arise.
In contrast, Wi-Fi devices operate only within two limited frequency bands: 2.4 and 5 GHz. Below are several issues that one might need to overcome or at least be aware of.
Problem One — different standards operate within different frequency bands.
In the 2.4 GHz band, devices supporting the 802.11b/g standard operate, while in the 5 GHz band, devices of the 802.11a and 802.11n standards are in use.
As we can see, only devices that comply with the 802.11n standard can operate in both the 2.4 GHz and 5 GHz bands. In other cases, we must either support broadcasting in both bands or accept that some clients will not be able to connect to our network.
Problem Two — Wi-Fi devices operating within close range 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 standards are available and permitted for use in Russia, or 40 MHz for the 802.11n standard with 5 MHz gaps.
Therefore, any wireless device (client or access point) creates interference on neighboring channels. However, the power of the transmitter in a client device, such as a smartphone, is significantly lower than that of a typical access point. Thus, throughout the article, we will only discuss the mutual influence between access points.
The most commonly suggested default channel for clients is 6. However, one should not be misled into thinking that choosing a neighboring number will eliminate interference. An access point operating on channel 6 causes strong interference on channels 5 and 7, and weaker interference on channels 4 and 8. As the gaps between channels increase, their mutual influence decreases. Therefore, to minimize mutual interference, it is highly desirable for their carrier frequencies to be separated by 25 MHz (5 inter-channel gaps).
The problem is that among all the channels with minimal influence on each other, only 3 are available: 1, 6, and 11.
We must find a way to circumvent existing limitations. For example, the mutual influence of devices can be compensated by reducing power.
On the benefits of moderation in everything
As mentioned above, reducing power is not always a bad thing. Moreover, increasing power can significantly degrade reception quality, and this has nothing to do with the 'weakness' of the access point. Below we will discuss when this can be useful.
Loading the radio spectrum
The effect of congestion can be observed in real time when selecting a device to connect. If there are more than three or four options in the Wi-Fi network selection list, we can talk about radio frequency congestion. Each network acts as a source of interference for its neighbors. Interference affects network performance by significantly increasing noise levels, necessitating constant resending of packets. In this case, the main recommendation is to reduce the transmitter power at the access point, ideally convincing all neighbors to do the same to avoid disturbing one another.
The situation is reminiscent of a school classroom during a lesson when the teacher steps out. Each student begins to talk to their desk mate and other classmates. In the general noise, they struggle to hear one another and start speaking louder, then even louder, eventually leading to shouting. The teacher quickly returns to the classroom, takes some disciplinary actions, and normalcy is restored. If we imagine the network administrator as the teacher and the access point owners as the students, we have a nearly direct analogy.
Asymmetric connection
As mentioned earlier, the power of the access point's transmitter is usually 2-3 times stronger than that of client mobile devices: tablets, smartphones, laptops, and so on. Therefore, it's quite likely to encounter 'gray areas' where the client receives a good stable signal from the access point, but the transmission from the client to the point may not be very effective. This type of connection is referred to as asymmetric.
To maintain a stable connection with good quality, it is highly desirable for there to be a symmetric connection between the client device and the access point, where both reception and transmission work effectively in both directions.
Figure 1. Asymmetric connection illustrated with an apartment layout example.
To avoid asymmetric connections, one should refrain from thoughtlessly increasing the transmitter power.
When an increase in power is required
The factors listed below necessitate an increase in power 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 frequency range, can interfere with access points and other Wi-Fi devices.
The devices listed below can also negatively affect signal quality:
- microwave ovens;
- baby monitors;
- CRT monitors, wireless speakers, wireless phones, and other wireless devices;
- external sources of electrical voltage, such as power lines and substations,
- electric motors;
- cables with insufficient shielding, as well as coaxial cables and connectors used with certain types of satellite dishes.
Long distances between Wi-Fi devices
Any radio devices have a limited range. Besides the design features of the wireless device, the maximum reachable distance can be reduced by external factors such as obstacles and radio interference.
All this leads to the formation of local "dead zones" where the signal from the access point does not reach the client device.
Obstacles to signal transmission
Various obstacles (walls, ceilings, furniture, metal doors, etc.) located between Wi-Fi devices can reflect or absorb radio signals, resulting in degraded signal quality or complete loss of connection.
Simple and common things, like reinforced concrete walls, metal sheet coverings, steel frameworks, and even mirrors and tinted glass noticeably decrease signal intensity.
Interesting fact: the human body weakens the signal by approximately 3 dB.
Below is a table showing the loss of Wi-Fi signal effectiveness when passing through various media for a 2.4 GHz network.
* Effective range — indicates the degree of reduction in the effective range after passing through the corresponding obstacle compared to open space.
Let’s summarize the findings
As mentioned above, high signal strength alone does not improve Wi-Fi connection quality but can hinder the establishment of a good connection.
At the same time, there are situations where higher power is required for stable transmission and reception of Wi-Fi radio signals.
Such contradictory demands exist.
Useful features from Zyxel that can help.
Clearly, one needs to use some interesting features that can help navigate this contradictory situation.
IMPORTANT! You can learn about many nuances in building wireless networks, as well as the capabilities and practical use of equipment, at specialized Zyxel courses — ZCNE. Find out about the nearest courses. .
Client Steering
As noted earlier, the described issues mainly affect the 2.4GHz band.
Happy owners of modern devices can use the 5GHz frequency band.
Advantages:
- more channels, making it easier to choose those that will minimally interfere with each other;
- other devices, such as Bluetooth, do not use this band;
- support for channel widths of 20/40/80 MHz.
Disadvantages:
- Radio signals in this band pass through obstacles worse. Therefore, it is advisable to have not one "super-penetrating" access point, but two or three with a more modest signal power in different rooms. On the other hand, this provides a more even coverage pattern than trying to catch a signal from one extremely powerful point.
However, in practice, as always, there are nuances. For example, some devices, operating systems, and software still default to offering the "old reliable" 2.4GHz band for connection. This is done to reduce compatibility issues and simplify the network connection algorithm. If the connection occurs automatically or the user does not notice this fact — the possibility of using the 5GHz band will remain overlooked.
The Client Steering feature can help change this situation, which by default encourages client devices to connect through 5GHz. If this band is not supported by the client, it can still use 2.4GHz.
This feature is available:
- in Nebula and NebulaFlex access points;
- in NXC2500 and NXC5500 wireless network controllers;
- in firewalls with controller functionality.
Auto Healing
Many arguments have been presented in favor of flexible power regulation. However, a reasonable question remains: how can this be achieved?
For this purpose, Zyxel's wireless network controllers have a special function: Auto Healing.
With its help, the controller checks the status and functionality of access points. If one of them is found to be non-functional, neighboring points are instructed to increase their signal power to fill the created silence zone. Once the missing access point is back online, neighboring points are instructed to reduce their signal power to avoid interference with each other.
This function is also present in a special line of wireless network controllers: NXC2500 and NXC5500.
Secure wireless network boundary
Neighboring access points from a parallel network not only create interference but can also be used as a platform for attacks on the network.
In turn, the wireless network controller must combat this. The NXC2500 and NXC5500 controllers are equipped with sufficient tools, such as standard WPA/WPA2-Enterprise authentication, various implementations of the Extensible Authentication Protocol (EAP), and a built-in firewall.
Thus, the controller not only detects unauthorized access points but also blocks suspicious activities within the corporate network that are likely to carry malicious intent.
Rogue AP Detection (Rogue AP Containment)
First, let's clarify what a Rogue AP is.
A Rogue AP is an unauthorized access point that is not under the control of the network administrator. Nevertheless, it is present within the range of the enterprise's Wi-Fi network. For example, these could be personal access points of employees connected to network sockets in the office without permission. Such self-activity negatively impacts network security.
In fact, such devices create a channel for unauthorized access to the enterprise network, bypassing the main security system.
For example, a foreign access point (Rogue AP) is technically not part of the corporate network, but it has a wireless network established with the same SSID name as the legal access points. As a result, the Rogue AP can be used to intercept passwords and other confidential information when clients of the corporate network mistakenly attempt to connect to it and try to transmit their credentials. Consequently, users' credentials will be known to the owner of the phishing point.
Most access points from Zyxel come with a built-in feature for scanning radio frequencies to detect foreign points.
IMPORTANT! The detection of foreign access points (AP Detection) will only work if at least one of these 'watchdog' access points is configured to operate in network monitoring mode.
Once the Zyxel access point, operating in monitoring mode, detects foreign points, a blocking procedure can be initiated.
Let's say the Rogue AP mimics a legitimate access point. As mentioned earlier, the attacker can replicate corporate SSID settings on the fake point. The Zyxel access point will then attempt to thwart the malicious activity by sending out distracting broadcast dummy packets. This will prevent clients from connecting to the Rogue AP and having their credentials intercepted. The 'spy' access point won’t be able to carry out its mission.
As we can see, the mutual influence of access points not only creates annoying interference with each other's operation but can also be used to protect against attackers' assaults.
Conclusion
The material within a small article does not allow for a detailed exploration of all nuances. However, even a brief overview makes it clear that the development and maintenance of a wireless network have quite interesting considerations. On 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’s essential to maintain a sufficiently high signal level for stable connectivity.
This contradiction can be circumvented by using special features provided by wireless network controllers.
It is also worth noting that Zyxel is working on improving everything that helps achieve quality communication without incurring high costs.
file — continuous reading of events from one or more local files;
Source: habr.com
