【Typical Case】How to Troubleshoot Low Speeds of Wireless Clients Connected to AP840-L？

Keywords:

AP840-L, WLAN Speed Test
Issue Description

(1) The measured wireless rate and negotiated rate for clients connected to the AP840-L are low.



Device Model and Firmware

Device Type	Device Model	Firmware Version
Access  switch	WS-C2960X-48LPS-L	N/A
Access  point	AP840-L	AP_RGOS  11.9(6)W3B1, Release(11160201)

Cause Analysis

• Check the information of abnormal wireless clients, including their MAC addresses and wireless network adapter details.Check whether the wireless network adapter can obtain a higher rate.
  

2. Check the configurations and negotiated rate on the AP associated with the abnormal wireless clients. It is found that the negotiated rate is only 433 Mbps on the 80 MHz channel.

3. Check the PoE power supply. The power supply mode is set to 802.3af. When the AP operates in this mode, it can only provide a single spatial stream due to insufficient power. As a result, both the negotiated rate and the measured rate for the wireless client are low.

Root Cause

The Cisco switch provides power to the AP840-Lin 802.3af mode, which is insufficient. As a result, the rate measured by the wireless client is low.

Solution

1. When a Cisco switch is connected to the AP840-L, the switch can only provide power to the AP840-L in 802.3af mode by default. If the AP840-L is forcibly configured to operate in 802.3at mode, it may restart abnormally. The following solutions can be implemented to enable 802.3at power supply for the AP840-L:
(1)Solution 1 (when AP840-L works in 802.3af mode): Set the power supply mode on the Cisco switch to Auto mode, and run the pd poe-force af command on the AP840-L.
(2) Solution 2 (when AP840-L works in 802.3at mode): Set the power supply mode on the Cisco switch to Static mode (PoE output power of 30 W) and configure the AP to work in 802.3at mode (PoE output power of 25 W).
2. After Solution 2 is implemented to solve the power supply issue, the speed of wireless clients connected to the AP840-L can reach the expected value.