High-Density WiFi. Part 1: Pass to the Premier League. Part 2: Approaches
“You shall know them by their works.”
Matthew 7:20
Today in the market of wireless technologies there is a situation when WiFi does not make decisions only lazy. Chinese vendors, American vendors, European vendors, Israeli vendors, Russian vendors ... all produce "wireless solutions for corporate networks." But, as in football, there is Real Madrid, Chelsea and Bavaria, and there is Pakhtakor and Dijon, with all due respect. Both are running around the field 68 by 105 meters and kicking the ball, trying to get into frame 7 by 2.5. But the whole question is not “WHAT THEY DO”, but “HOW THEY DO IT”.
If you, as a corporate customer, need to have “five sticks” of WiFi at the entrance to your office, then this task will be solved quickly for you by many small and not so great manufacturers. Everyone will assure that meets all standards and meets all your requirements and will do everything “quickly, well and inexpensively”, contrary to the well-known principle. BUT. If your task is to
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then you definitely have to choose someone from the Premier League. In this place there is a legitimate and most important question for people, not deep in the topic - and how to choose from all this information noise? Everybody pokes you with tests, projects, customers and speaks about the vast experience and the best solutions in the world ... My advice to you, as written in the correct books, is “You will recognize them by their deeds”.
There are several distinguishing features of the manufacturer, the presence of which ranks the company in the WiFi Premier League, without any doubt and despite the wiles of competitors. And one of them is the ability to successfully implement the so-called High Density (HD) projects. High Density is when a very large number of people gather in a limited space and almost every one of them needs high-quality Internet access (for example, WiFi in the stadium of thousands for 80 people). To understand the complexity of this task, you need to remember school physics and its concept as Interference. Still it is necessary to remember that a radio resource is a finite and limited thing. Moreover, in WiFi this thing is also shared. That is, literally, you have two bands (2.4 and 5 GHz), and each band has a clear set of radio channels (1, 6, 11, etc.) of a certain width (20, 40, 80 and 160 Mhz) (for those interestingly deeper into theory - here ), each of which, depending on the type of modulation, gives you a certain bandwidth in Mbit / s and which can not be more than by design. This means that the entire WiFi infrastructure shares this final set of radio channels and acts as an arbiter of user access to this common environment. Here it is impossible to bring each user the same carrier over a shielded copper pair, as in Ethernet. And here the very important role played by the interference in all forms. Users start “jamming” each other due to interference at the boundaries of the ranges, by placing them on one channel on neighboring points, data begin to accumulate in buffers ... ultimately, the network should not work properly.
Figure 1. Competitive access to the radio environment
And, instead of improving the quality of communication with an increase in the number of points, the opposite effect occurs - its deterioration. Add to this:
and you will understand how complex and multifaceted is the task of constructing an WORKING HD WiFi. In no case can this problem be solved by simply increasing the number of points, as it is sometimes done - it is written in the datasheet, conventionally, 50 active users per point, divide 80,000/50 and get 1600 points per stadium. We place points under the lamps and seats, launch the network, make sure in the first match that WiFi is not working and further options are possible:
The conclusion is simple - only a company that truly understands how modern WiFi networks work, which has people who can design, implement and maintain such an infrastructure and, most importantly, which have the tools from which to build such an infrastructure, can successfully make HD WiFi . Therefore, I can say that the presence in the company's portfolio of such successfully implemented projects (and, therefore, such resources and expertise) uniquely identifies it in the WiFi Premier League.
“- These entities are more advanced than us. Why don't they?
“You're more advanced than a cockroach, have you ever tried explaining yourself to one of them?”
The mothman prophecies
Let's now talk about how and with the help of what technologies HD WiFi can and should be implemented. As mentioned above, the main scourge of HD WiFi is interference and the total network capacity determines the number of radio channels, not the number of access points. The interference can be divided into two types - Adjacent Channel Interference (ACI) and Co-Channel Interference (CCI). ACI is when two channels intersect at the boundary of the spectra and the energy emitted outside the range limits increases the level of radio noise in adjacent channels and, as a result, the number of errors, which is especially relevant in the 2.4 GHz band, where there are only 3 non-overlapping channels. This type of interference is usually , does not have a significant impact in conventional corporate WiFi networks, because the average distance between points in such networks is about 20 meters, which, with standard losses of 80dB for 5 GHz, provides sufficient isolation and the Clear Channel Assessment (CCA) does not see the 802.11 frame for the mechanisms, does not detect collisions, and does not mark the free channel as busy. A completely different story is obtained when building HD WiFi. Here, the points are located so close to each other that ACI is determined by the CCA mechanisms as collisions and the neighboring channels turn, in fact, into one collision domain with all the consequences. To make it clearer, let's look at a simple example of what happens in such a case.
Figure 2. ACI
Suppose the points are apart as shown in Figure 2 and the station 2 / point 2 wants to transmit data. They run CCA and, because the distance between them and neighboring stations / points is less than a meter, then signals on adjacent channels (36th and 44th) due to ACI exceed the CCA threshold and are considered as a collision. Station 2 / point 2 is silent, considering that the channel is busy.
CCI-type interference (when different points / stations are on the same channel and hear each other due to the proximity of sources) has an even greater negative effect on the HD WiFi network than ACI. Even if the channels are not reused indoors, modern NICs in devices are so sensitive that they can catch external sources on the same channels and define it as a collision.
Figure 3. CCI
If the device picks up an 802.11 frame on its radio channel, it cannot transmit data and waits until the transmitted frame ends.
What do the Premier League vendors know how to do to defeat physics and smooth out the negative effects of the dense use of the radio environment? To make the conversation substantive, let's define, and what, as a rule, want from HD WiFi, if you decrypt the common "to work". They usually want a solution:
One of the best solutions on the market that meets the above requirements and is able to solve the problem of building HD WiFi is a solution from Aruba, whose high-level architecture is as follows:
Figure 4. HD WiFi architecture
Conventionally, for ease of description, it can be divided into the following large blocks:
Below I will talk about each block in more detail, but first you need to say a few words about the principles of the physical design of HD networks and the calculation of coverage. There are several obvious options for the placement of points, more precisely the three main points - on the ceiling, on the walls and on the floor - plus various combinations of them.
Figure 5. Location of equipment
Each option has its advantages and disadvantages. The option of placing points on the ceiling is most common in corporate networks and has the following advantages:
The most important disadvantage of this option is the great difficulty with reusing channels, since with a high probability, with such an arrangement each point will be audible over the entire area of the HD coverage.
The option of placing points on the walls is not as common because of a number of difficulties and inconveniences that it carries with it. Firstly, this option also, like the version with placement on / under the ceiling, does not allow to reuse channels properly. Secondly, the level of attenuation in this variant is significantly higher and the level of the signal, as a rule, floats seriously. In addition, with this placement, it is difficult to control ACI / CCI and the signal often goes beyond the intended coverage area. Therefore, this placement option requires serious justification and is not often used.
The option of placing points on / under the floor in terms of achieving the maximum quality of the coating has the following advantages:
In addition to the correct physical alignment of points, in each specific case it is necessary to carry out a number of measures aimed at estimating coverage and choosing appropriate solutions, such as choosing, correct placement and correct orientation of antennas, careful assessment of radio link budgets (taking into account radiated power, antenna gain, absorption environmental radio emission). This is very important, because if you first calculate the coverage incorrectly or do not count it completely and / or arrange the equipment incorrectly, then you will not correct the situation with any manipulations and the network will work poorly.
As a result, you should get something like this coverage map:
Figure 6. Radio coverage of the stadium
After all the calculations have been made and verified, you can proceed to the placement of the equipment and the construction of the network.
To be continued.
Matthew 7:20
Today in the market of wireless technologies there is a situation when WiFi does not make decisions only lazy. Chinese vendors, American vendors, European vendors, Israeli vendors, Russian vendors ... all produce "wireless solutions for corporate networks." But, as in football, there is Real Madrid, Chelsea and Bavaria, and there is Pakhtakor and Dijon, with all due respect. Both are running around the field 68 by 105 meters and kicking the ball, trying to get into frame 7 by 2.5. But the whole question is not “WHAT THEY DO”, but “HOW THEY DO IT”.
If you, as a corporate customer, need to have “five sticks” of WiFi at the entrance to your office, then this task will be solved quickly for you by many small and not so great manufacturers. Everyone will assure that meets all standards and meets all your requirements and will do everything “quickly, well and inexpensively”, contrary to the well-known principle. BUT. If your task is to
')
- User Experience Index did not fall to the floor,
- so that everyone who connects to your network gets real service, not rotating watches,
- so that once a week you will not be cracked by youngsters with the help of hacker kits from the Internet and
- so that you do not roam agonizingly with the scanner, looking for where ... which includes microwaves that "put" your network,
then you definitely have to choose someone from the Premier League. In this place there is a legitimate and most important question for people, not deep in the topic - and how to choose from all this information noise? Everybody pokes you with tests, projects, customers and speaks about the vast experience and the best solutions in the world ... My advice to you, as written in the correct books, is “You will recognize them by their deeds”.
There are several distinguishing features of the manufacturer, the presence of which ranks the company in the WiFi Premier League, without any doubt and despite the wiles of competitors. And one of them is the ability to successfully implement the so-called High Density (HD) projects. High Density is when a very large number of people gather in a limited space and almost every one of them needs high-quality Internet access (for example, WiFi in the stadium of thousands for 80 people). To understand the complexity of this task, you need to remember school physics and its concept as Interference. Still it is necessary to remember that a radio resource is a finite and limited thing. Moreover, in WiFi this thing is also shared. That is, literally, you have two bands (2.4 and 5 GHz), and each band has a clear set of radio channels (1, 6, 11, etc.) of a certain width (20, 40, 80 and 160 Mhz) (for those interestingly deeper into theory - here ), each of which, depending on the type of modulation, gives you a certain bandwidth in Mbit / s and which can not be more than by design. This means that the entire WiFi infrastructure shares this final set of radio channels and acts as an arbiter of user access to this common environment. Here it is impossible to bring each user the same carrier over a shielded copper pair, as in Ethernet. And here the very important role played by the interference in all forms. Users start “jamming” each other due to interference at the boundaries of the ranges, by placing them on one channel on neighboring points, data begin to accumulate in buffers ... ultimately, the network should not work properly.
Figure 1. Competitive access to the radio environment
And, instead of improving the quality of communication with an increase in the number of points, the opposite effect occurs - its deterioration. Add to this:
- an uncontrollable mix of user devices with different capabilities, different operating systems, levels of patches, drivers and types of radio
- high probability of each user having multiple devices
- the limitations of most modern devices to work in 1x1: 1 mode HT20
- interference with mobile networks LTE-A
- increased load on the control plane as a result of mass power-on switching on end devices
- floating load on the network, with a difference of hundreds of times
and you will understand how complex and multifaceted is the task of constructing an WORKING HD WiFi. In no case can this problem be solved by simply increasing the number of points, as it is sometimes done - it is written in the datasheet, conventionally, 50 active users per point, divide 80,000/50 and get 1600 points per stadium. We place points under the lamps and seats, launch the network, make sure in the first match that WiFi is not working and further options are possible:
- integrator / vendor "call on the carpet", there is a rapid explanation, the integrator / vendor is going to learn mate. part and try to rectify the situation in a living way (it turns out, as a rule, bad),
- the integrator / vendor is “called to the carpet”, there is a stormy explanation and a swap of the whole project to someone from the Premier League who can do it,
- ...
The conclusion is simple - only a company that truly understands how modern WiFi networks work, which has people who can design, implement and maintain such an infrastructure and, most importantly, which have the tools from which to build such an infrastructure, can successfully make HD WiFi . Therefore, I can say that the presence in the company's portfolio of such successfully implemented projects (and, therefore, such resources and expertise) uniquely identifies it in the WiFi Premier League.
Part 2. About approaches
“- These entities are more advanced than us. Why don't they?
“You're more advanced than a cockroach, have you ever tried explaining yourself to one of them?”
The mothman prophecies
Let's now talk about how and with the help of what technologies HD WiFi can and should be implemented. As mentioned above, the main scourge of HD WiFi is interference and the total network capacity determines the number of radio channels, not the number of access points. The interference can be divided into two types - Adjacent Channel Interference (ACI) and Co-Channel Interference (CCI). ACI is when two channels intersect at the boundary of the spectra and the energy emitted outside the range limits increases the level of radio noise in adjacent channels and, as a result, the number of errors, which is especially relevant in the 2.4 GHz band, where there are only 3 non-overlapping channels. This type of interference is usually , does not have a significant impact in conventional corporate WiFi networks, because the average distance between points in such networks is about 20 meters, which, with standard losses of 80dB for 5 GHz, provides sufficient isolation and the Clear Channel Assessment (CCA) does not see the 802.11 frame for the mechanisms, does not detect collisions, and does not mark the free channel as busy. A completely different story is obtained when building HD WiFi. Here, the points are located so close to each other that ACI is determined by the CCA mechanisms as collisions and the neighboring channels turn, in fact, into one collision domain with all the consequences. To make it clearer, let's look at a simple example of what happens in such a case.
Figure 2. ACI
Suppose the points are apart as shown in Figure 2 and the station 2 / point 2 wants to transmit data. They run CCA and, because the distance between them and neighboring stations / points is less than a meter, then signals on adjacent channels (36th and 44th) due to ACI exceed the CCA threshold and are considered as a collision. Station 2 / point 2 is silent, considering that the channel is busy.
CCI-type interference (when different points / stations are on the same channel and hear each other due to the proximity of sources) has an even greater negative effect on the HD WiFi network than ACI. Even if the channels are not reused indoors, modern NICs in devices are so sensitive that they can catch external sources on the same channels and define it as a collision.
Figure 3. CCI
If the device picks up an 802.11 frame on its radio channel, it cannot transmit data and waits until the transmitted frame ends.
What do the Premier League vendors know how to do to defeat physics and smooth out the negative effects of the dense use of the radio environment? To make the conversation substantive, let's define, and what, as a rule, want from HD WiFi, if you decrypt the common "to work". They usually want a solution:
- well scaled (talking about hundreds and thousands of access points to infrastructure),
- Stable performance on mixed traffic patterns at maximum loads (10,000+ users),
- potentially integrated with the core of mobile operators to provide 3G / 4G mobile offload,
- allowed flexible differentiation of access policies for different groups of users, supported different types of authentication / authorization,
- it was safe, i.e. covered the whole range of measures to ensure information security in a wired network, and in the radio environment,
- easy to set up and had a center console from which you could manage the entire network from one point
One of the best solutions on the market that meets the above requirements and is able to solve the problem of building HD WiFi is a solution from Aruba, whose high-level architecture is as follows:
Figure 4. HD WiFi architecture
Conventionally, for ease of description, it can be divided into the following large blocks:
- Radio optimization
- Comprehensive Security
- Optimize media traffic
- Centralized management
Below I will talk about each block in more detail, but first you need to say a few words about the principles of the physical design of HD networks and the calculation of coverage. There are several obvious options for the placement of points, more precisely the three main points - on the ceiling, on the walls and on the floor - plus various combinations of them.
Figure 5. Location of equipment
Each option has its advantages and disadvantages. The option of placing points on the ceiling is most common in corporate networks and has the following advantages:
- The points can be hidden under the ceiling and only the antennas are brought out.
- Uniform distribution of the signal and points
- Points are always in line of sight to client devices.
- Minimal signal attenuation by humans
- Good control of both types of interference (CCI / ACI)
The most important disadvantage of this option is the great difficulty with reusing channels, since with a high probability, with such an arrangement each point will be audible over the entire area of the HD coverage.
The option of placing points on the walls is not as common because of a number of difficulties and inconveniences that it carries with it. Firstly, this option also, like the version with placement on / under the ceiling, does not allow to reuse channels properly. Secondly, the level of attenuation in this variant is significantly higher and the level of the signal, as a rule, floats seriously. In addition, with this placement, it is difficult to control ACI / CCI and the signal often goes beyond the intended coverage area. Therefore, this placement option requires serious justification and is not often used.
The option of placing points on / under the floor in terms of achieving the maximum quality of the coating has the following advantages:
- It allows you to reuse channels
- Points as well as with the placement of the ceiling, you can hide
- The signal covers the area evenly.
- Points are always in line of sight to client devices.
- Minimal signal attenuation by humans
- Good Interference Control (CCI / ACI)
In addition to the correct physical alignment of points, in each specific case it is necessary to carry out a number of measures aimed at estimating coverage and choosing appropriate solutions, such as choosing, correct placement and correct orientation of antennas, careful assessment of radio link budgets (taking into account radiated power, antenna gain, absorption environmental radio emission). This is very important, because if you first calculate the coverage incorrectly or do not count it completely and / or arrange the equipment incorrectly, then you will not correct the situation with any manipulations and the network will work poorly.
As a result, you should get something like this coverage map:
Figure 6. Radio coverage of the stadium
After all the calculations have been made and verified, you can proceed to the placement of the equipment and the construction of the network.
To be continued.
Source: https://habr.com/ru/post/303248/
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