I dare say 99.9% of network engineers don’t know the four major indicators for locating wireless network failures!

1. Related concepts

1. Noise Floor

Definition: It refers to the noise present in communication systems or electronic devices when there is no useful signal. It is an inherent noise caused by a variety of physical phenomena and electronic component characteristics.

When the average noise floor value detected by the AP is higher than -80, you need to be alert, as the wireless environment may not be ideal:

2. Channel Utilization

Definition: Channel utilization refers to the ratio of the time actually used to transmit valid data to the total available time on a communication channel. It reflects the degree to which channel resources are effectively utilized.

Calculation: Channel utilization = (time for transmitting valid data / total available time) × 100%. For example, if a channel transmits valid data for 6 seconds out of 10 seconds, then the channel utilization is (6/10) × 100% = 60%. Generally speaking, when the channel rate is higher than 60%, it means that the radio frequency is busy.

3. Receive air interface utilization

Definition: The ratio of the air interface resources actually used by the receiving end to receive data to the total air interface resources. It is used to measure the utilization of wireless resources by the receiving end.

Calculation: Receive air interface utilization = (air interface resources occupied by received data / total air interface resources) × 100%. A larger value indicates that the AP's wireless data reception is more severely blocked.

4. Send air interface utilization

Definition: The ratio of the air interface resources (such as wireless frequency band) actually occupied by the sender to send data to the total air interface resources. It is mainly used to measure the efficiency of the sender's use of wireless resources.

Calculation: Sending air interface utilization = (air interface resources occupied by sending data / total air interface resources) × 100%. The larger the value, the more serious the obstruction to AP wireless data reception.

Taking H3C AP as an example, you can view its radio frequency information:

Now that we have a brief understanding of the four wireless indicators above, how do we determine the cause of wireless network failure? Let’s continue reading.

2. Wireless Index Analysis

The background noise is a fixed value that depends on the wireless environment. When there are strong non-WIFI or WIFI-like interference devices such as microwave ovens, industrial welding machines, and communication base stations in the on-site environment, the background noise will become larger, that is, the "wireless environment is not clean". It is like you want to drive a sports car but the road is bumpy. It is impossible to adjust the AC and AP. The only way to do this is to physically remove them and manually communicate to clear the obstacles.

Engineers should pay more attention to the three indicators of channel utilization, receiving air interface utilization and transmitting air interface utilization. Generally speaking, since wireless works in "half-duplex", the sum of the receiving and transmitting air interface utilization of the AP will not exceed 100%. In most cases, wireless performance anomalies are caused by one-way obstruction. The following scenarios:

1. RX is much greater than TX: the receiving air interface utilization is 80, and the sending air interface utilization is 5

That is, the AP receiving air interface utilization is much greater than the sending air interface utilization and the sum of the two is greater than 80, indicating that the AP RX direction is severely blocked. The reason for this problem is that the AP receives too many wireless frames of the same frequency.

Typical cases are:

• There are too many adjacent/same-frequency APs that are visible to each other and compete for channel resources, resulting in high utilization.
• Too many SSIDs, a large number of Beacon frames fill the wireless network, causing the utilization rate to soar

2. RX is much smaller than TX: the receiving air interface utilization is 5, and the sending air interface utilization is 80

That is, the AP receiving air interface utilization is much smaller than the sending air interface utilization and the sum of the two is greater than 80, indicating that the AP TX direction is severely blocked. The reason for this problem is that the AP sends a large amount of data and occupies the air interface resources.

Typical cases are:

• Broadcast and multicast flooding on the wired side of the AP. AP flooding broadcast and multicast to the wireless side will greatly consume air interface resources.
• The AP is bound to too many SSIDs and the beacon transmission interval is small. In this way, the AP will wirelessly broadcast too many beacon frames quickly, resulting in high air interface utilization.

3. Channel utilization >> Receive air interface utilization + Send air interface utilization

Because the reception and transmission air interface utilization statistics are based on WiFi frames and cannot identify non-WiFi signal waves, if the AP finds that its reception/transmission air interface utilization is not high, but the sum of the two is much smaller than the channel utilization, it means that there are no major problems with the AP's packet reception and transmission, but the wireless experience is still very poor. This can be considered as non-WiFi interference in the environment.