Is the wireless network unstable? Dig out four major killers

After installing a wireless network, you may find that the network does not support your applications as well. Users may complain about unstable connections and poor performance, which will impede application use. As an administrator, You need to diagnose the fault. First, find the root cause of the problem.

The following table may give you some guidance. You may wish to see this table when you encounter a fault. Here, we need to note that the signal strength, noise intensity, retry rate, and other factors are related to the underlying causes of poor wireless network performance.

RF interference

RF interference will occupy the wireless transmission media such as air, delay the time when users send and receive data, and cause conflicts, resulting in data re-transmission. If the noise intensity is high and the retry rate is high, you can see from the above table that this is generally caused by RF interference that is affecting your wireless network. I suggest you use NetStumbler and other tools to test the noise. In addition, most Access Point Ap stores the information about the number of trials. You can view the information on the Management Console. If the network performance drops, it is a good step to view the number of retries.

If the noise intensity in your network bandwidth exceeds-85dBm, RF interference may damage network performance. In this case, the user's retry rate will exceed 10%, then the user will feel the network speed is affected. For example, this happens when a wireless user is in the same room as a running microwave oven.

If you decide the problem is caused by RF interference, you have to find out where the interference comes from and try to remove it. If this problem occurs only in a microwave or wireless phone, you have to try to place the AP access point on different channels.

In addition, you need to check whether there are other wireless networks nearby. If you find that someone else uses the same channel as you, you have to change your network to a non-conflicting channel. Remember, only three channels (1, 6, and 11) do not conflict with each other in the GHz bandwidth. Most home and small office sites set their AP access points to use 6 channels, because this is the most common default channel set by the vendor. Therefore, you may need not to allow access points outside the enterprise to use this channel.

If you still cannot reduce the RF interference to an acceptable level, you can try to increase the RF signal strength in the affected area. For example, you can increase the transmit power to replace the original antenna with a stronger unit, or make the access point closer. This method increases the signal-to-noise ratio (the ratio of the average signal to the random noise of a data unit) to improve performance.

High utilization

When there are too many active wireless network users, or when users are operating applications that consume too much bandwidth (such as downloading large files ), applications on the network may reach the maximum capacity of the Access Point. In this case, the retry rate may be relatively higher (more than 10%), even if the signal strength is high and the noise intensity is very low, it will affect the network performance (that is, the signal-to-noise ratio is very high ). The result is that extra time is spent to re-transmit the data frame, resulting in reduced throughput.

There are still some solutions. You can place the Access Point AP closer at a lower power to create a smaller RF cell. This "micro-cellular" method can reduce the number of users in each access point, so that each user can get more capacity.

Another way to cope with high network utilization is to move some applications to a different band. For example, you can consider using a 5 GHz 802.11a network for a Wi-Fi Phone, and running a data application on a 2.4 GHz 802.11b/g. Network.

Coverage vulnerabilities (blind spots)

After the wireless network is installed, some changes may occur in the adjustment of RF signal transmission facilities. For example, a company may need to build a wall, which can greatly weaken the signal. Worse, the RF location may not be investigated before the network is installed. These situations will lead to limited or even no RF signals in some areas of the Facility, which will greatly reduce performance and interrupt the operation of wireless applications.

Which of the following aspects indicate the coverage of vulnerabilities? This includes low signal strength (lower than-75dBm), too high retry rate (higher than 10%), but not noise intensity. In this case, the signal strength is too low, so the wireless card receiver is quite difficult to obtain data, resulting in retransmission and low throughput. For example, when a user operates at a low signal intensity, he may feel that the throughput has dropped by as much as 75%.

To cope with the coverage vulnerabilities, users need to improve the signal strength of the affected areas. Try to increase the sending power, replace the old antenna with a stronger antenna, or overwrite the entire area with an AP. To minimize coverage vulnerabilities in the wireless network in the future, I suggest you conduct frequent RF field surveys and measurements, such as the last time every few months.

Access Point too bad

Sometimes, the root cause of poor network performance may be that an AP Access Point has failed. You can check the access point to see if the antenna is disconnected, whether the status light indicates an error or the power supply is insufficient. You can try to restart the AP, which usually solves the deadlock problem of the firmware. To keep the firmware updated, we aim to reduce deadlocks in the future.