How many devices can a wireless AP and a wireless bridge carry? One article to find out

Many friends asked me, what is the capacity of a wireless AP? Some friends also mentioned the capacity of a wireless bridge? We have mentioned this before. To understand their capacity, we have to understand the performance indicators of the AP. So let's summarize the issue of capacity in this issue.

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1. What factors should be considered before choosing an AP?

When doing wireless coverage projects, wireless AP selection needs to be based on networking requirements and application scenarios, among which the capacity of wireless AP is an important reference factor. However, in general, a single AP may not be able to achieve the capacity claimed by the merchant, because there are many factors that affect the capacity of wireless AP, such as broadband size, number of access devices, chips, memory, etc., which will become factors affecting the capacity of AP. All of this starts with the working principle of wireless AP.

When selecting APs for wireless coverage, the following should be considered:

Environmental characteristics: outdoor or indoor, sparsely distributed terminals (such as warehouses) or high-density wireless access (such as conference rooms, multi-function halls, etc.).

Installation method: ceiling, panel or 86 box type.

Power supply mode: standard PoE (802.3af or 802.3at), Passive PoE or DC (direct current power supply).

Coverage: single room, multiple rooms, area coverage, fixed-point coverage, etc.

Frequency: 2.4g and 5.g, single band and dual band.

Capacity: A single AP can connect to 10, 20, 30 or 50 terminals.

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The number of wireless APs on the market is different, with different manufacturers claiming different numbers of devices, ranging from 25, 50, 100, to 200. Are they really as high as claimed?

In fact, there is no standard answer to how many terminal users a wireless AP can connect to, because the network application situations in various usage scenarios are ever-changing, and the terminal devices used are also different. It is difficult to conduct a standard test method, so many manufacturers estimate the number of machines based on typical application environments.

Therefore, in order to ensure that the communication speed of the entire wireless network is not affected, a single AP needs to control the number of wireless terminals connected, which is what we often call the bandwidth, so as to ensure that each terminal can obtain sufficient Internet bandwidth.

As for the impact of the hardware configuration of the wireless AP on its throughput, it mainly refers to the chip and memory size. The better the chip, the greater the throughput; memory is also a factor that affects the throughput.

2. What factors are related to the wireless AP capacity?

Here we use an example to illustrate:

Take an AP as an example. We usually see that it has many parameters. Basically, every AP has these parameters. What do they mean?

Let's analyze the common parameters of AP:

1. Dual-frequency and single-frequency:

The dual-band APs on the market now are those that support both 2.4G and 5G. In our practical experience, the number of APs that can be supported by a single-band AP is basically difficult to exceed 40. The number of APs that can be supported by a dual-band AP is much higher. The performance of a 5.8G dual-band AP may be twice that of a single-band AP. Therefore, if it is a high-density access site, it is strongly recommended to use a dual-band AP.

2. The difference between 2.4g and 5g frequency range (why use dual frequency):

2.4G frequency is the most widely used, supported by almost all computers and smartphones. But because it is so common, even microwave ovens use the 2.4G frequency band, so there is a lot of interference, and serious interference will slow down the data transmission rate.

5G Wi-Fi was born to avoid the mutual interference problem, because this frequency is rarely used. Generally, wireless APs that support 5G based on 802.11ac technology can carry higher transmission rates. 5G also has disadvantages. The biggest problem is its poor wall penetration ability. The signal attenuation of 5G signals is very obvious after passing through a load-bearing wall.

so:

The lower the frequency, the better the wall penetration. The higher the frequency, the faster the speed. Currently, 2.4G is used by many people, and the interference from CMCC's WIFI signal is quite serious! 5G is not used much at present, and there is basically no interference, so dual-band AP can be used at both frequencies at the same time.

3. What is 802.11 a/b/g/n/ac?

First of all, 802.11 is a wireless LAN standard. 802.11 a/b/g/n/ac are all developed from 802.11. Different suffixes represent different physical layer standard working frequency bands and different transmission rates, that is, their physical layers and transmission speeds are different.

802.11b and 802.11g operate on the same frequency band, and g is compatible with b, which means that any network card that supports g can also support b.

The 802.11n protocol is a dual-band working mode (including 2.4GHz and 5GHz working frequency bands). In this way, 11n ensures compatibility with the previous 802.11ab and g standards, which means that when we choose an AP, we should check whether it has 802.11n parameters.

The new generation of WiFi standard 802.11 ac is developed from 802.11 n and has a higher speed than 802.11 n. The dual-band APs and routers on the market now support both 2.4G and 5G frequencies.

4. What is the wireless speed?

Although many APs have wireless rates of 450Mbps, 600Mbps, 750Mbps, and 1167Mbps, these rates are not actually achieved. Please see the list below for details.

The actual rate is about half of the theoretical rate. We can use this table to calculate the maximum capacity. The 802.11n standard APs currently used have an actual rate of 80Mbps-360Mbps. We can estimate their capacity based on bandwidth, and the upper limit is about 100. The new generation of wifi standard 802.11 ac has a higher rate and a higher capacity. Of course, the specific number depends on factors such as the AP chip, memory, and usage environment.

*** Let's talk about the number of terminals that wireless routers and wireless APs can carry. A home wireless router can carry 8 to 15 terminals, which is the limit. A general wireless AP can carry about 20 to 60 terminals. I would like to remind you, don't use home routers to cover wifi projects just to save money.

3. How many devices can a wireless bridge carry?

1. The relationship between the number of bridge devices

Regarding the number of pairings between wireless bridges and surveillance cameras, we need to consider three factors: the bandwidth occupied by the camera, the transmission distance, and the transmission bandwidth of the wireless bridge.

As long as we understand the relationship between these three, we can quickly determine the selection and quantity planning of wireless bridges and surveillance cameras in wireless monitoring projects.

The following is the calculation formula between the number of cameras and the wireless bridge transmission bandwidth:

Number of cameras = wireless bridge bandwidth / camera bit rate

Let me explain the bridge bandwidth here. It is somewhat different from the switch. Some of the bridges we usually buy are called gigabit bridges. Their actual capacity is not 1000M divided by the bit rate. The real-time transmission bandwidth of a bridge must be considered here. The actual transmission bandwidth of a 1000M bridge may be only about 100M, which means it can only support about a dozen 2-megapixel cameras.

2. To understand the capacity, you must first understand the transmission principle of the bridge

This is related to the transmission distance of the bridge as well as the performance, environment, and interference of the bridge. The bandwidth is limited to how many cameras can be connected. Of course, if the bit rate is smaller, more cameras can be connected in theory, but not more. It is complicated to explain this problem, but as long as you understand the working principle of WIFI, you will know that the bandwidth of the bridge is not the main factor. Time is the most important. The more cameras there are, the shorter the communication time for each camera. In the entire cycle, the data that cannot be fully processed in time is the upper limit. Therefore, once it cannot be processed in time, the bridge will become unstable, and problems such as card jamming or disconnection may occur.

3. To understand the capacity, you must first understand the transmission process of the bridge

In fact, to explain from another angle, the bridge is point-to-point transmission. Assume that a bridge device has a point-to-point bandwidth of 1000M, but when facing multiple camera access points, this bandwidth is meaningless. The camera transmits data that is closely related to time, and the bridge can only receive them one by one. No matter how large the unit bandwidth is, it will not play a big role. The data of the camera is collected in real time, which is different from sending and receiving data that has been stored on the hard disk. You will not get big data just because of the large bandwidth. The surveillance camera has no pre-reading mechanism and will not cache data for too long, so problems will arise if the data processing is slow.

If a camera's delay exceeds a certain time in a cycle, it will cause a comprehensive delay. The terminal will not recover until it abandons the old data and requests new data again, and then it will be delayed again. As a result, the picture will be stuck and the recorded content will lose time.

4. Transmission distance and bandwidth of wireless bridge

Everyone knows the relationship between transmission distance and transmission bandwidth. The longer the transmission distance, the smaller the transmission bandwidth. After all, wireless bridges use microwaves for transmission, and microwaves have a diffusion effect. When performing long-distance wireless transmission, microwave signals will be greatly weakened, just like the fact that the farther our mobile phones are from the WIFI source, the worse the signal.

Example

For example, a 5.8G high-power wireless bridge has a theoretical transmission rate of 300Mbps, but in actual applications, it is often only 60Mbps. If a 60Mpbs transmission rate is obtained in a 5km field test, then according to the above calculation formula, a 5km wireless transmission can carry 15 130W cameras with a bit rate of 4Mbps.

However, this is only possible in theory, after all, transmitting data is different from transmitting video. In wireless video surveillance projects, users pay great attention to the smoothness of surveillance videos. The bit rate of a 1.30W camera is 4Mbps, but when transmitting high-definition video, the dynamic bit rate in the transmission bandwidth may suddenly rise to 6Mbps or even higher.

Therefore, when this 5.8G wireless bridge performs 5km wireless transmission, it usually only carries about 10 130W cameras.

Of course, you can also increase the real-time transmission bandwidth of the wireless bridge by adding a high-gain antenna, so that you can carry one or two more cameras.

In addition, there are currently two video coding standards: H.264 and H.265.

The new video encoding technology H.265 can efficiently compress high-definition video, which is nearly twice as effective as H.264. Therefore, cameras that use H.265 video compression technology can also contribute to reducing transmission bandwidth.

5. The reference values ​​given here

According to the transmission distance, the bridge can be divided into 3km O5, 5km O3, and 10km O6. O3 is a 2.4G bridge, and O5/O6 is a 5G bridge. The transmission performance of the bridge decreases as the transmission distance increases. Taking point-to-point transmission as an example, the corresponding relationship table between the real-time bandwidth and distance of the bridge transmission is summarized for reference based on the data tested in the actual use environment.

6. Performance of wireless bridge

The performance of different wireless bridges determines their application environment. For example, a 5.8G high-power wireless bridge can transmit 5 kilometers, while another wireless bridge can transmit 50 kilometers, and there are even wireless bridges that can transmit 100 kilometers.

The difference in transmission distance depends on their performance, and there are many factors that affect their performance, such as the microwave frequency used, equipment power, hardware configuration, software, transmission technology, etc. In addition, because the 5.8G frequency band has less interference than the 2.4G frequency band and a faster transmission rate, generally speaking, for medium and long distance transmission, 5.8G wireless bridges can carry more cameras than 2.4G wireless bridges.