Troubleshooting AP Power Supply Downgrade Issues
Overview
This document introduces the basic concepts related to PoE and describes how to troubleshoot AP power supply downgrade issues.
Understanding Basic Concepts of PoE
What Is PoE?
Power over Ethernet (PoE) technology is a power supply technology based on Ethernet cables. It allows direct current (DC) to be transmitted to powered devices (PDs) through data line pairs or unused line pairs. This technology provides power over a 2.5GBASE-T, 1000BASE-T, 100BASE-TX, or 10BASE-T Ethernet network, spanning a distance of up to 100 m. PoE is used to effectively provide centralized power for terminals such as IP phones, wireless access points (APs), chargers of portable devices, point of sale (POS) terminals, cameras, and data collectors. Terminals are provided with power when they access the network. Therefore, indoor cabling of power supply is not required. As IP phones, network video surveillance, and wireless local area networks (WLANs) become more widely used, the power supply demand grows increasingly urgent.
The PoE power supply mode based on Ethernet cables has many advantages over the DC power supply mode and has been widely applied in people's production and life.
- Reliable: Multiple PDs are powered by a single power sourcing equipment (PSE), facilitating power backup.
- Easy to deploy: Network terminals can be powered over Ethernet cables, without the need for external power sources.
- Standard: PoE devices all over the world use unified power supply interfaces.
PoE Standards Compliance
A PoE power supply system consists of PSEs and PDs.
To ensure compatibility between PoE devices from different vendors, IEEE has released three sets of PoE standards, as described in Table 1-1.
PoE Standard |
IEEE 802.3af |
IEEE 802.3at |
IEEE 802.3bt |
|---|---|---|---|
Power supply technology |
PoE |
PoE+ |
PoE++ |
PSE output voltage |
44–57 V DC |
44–57 V DC |
bt60: 44–57 V DC bt90: 52–57 V DC |
PSE output power |
≤ 15.4 W |
≤ 30 W |
bt60: ≤ 60 W bt90: ≤ 90 W |
Maximum PD power |
12.95 W |
25.5 W |
bt60: 51 W bt90: 71.3 W |
Electrical signals transmitted over cables are inevitably attenuated. A longer power supply distance indicates higher loss. To ensure stable and reliable power supply, it is recommended that Ethernet cables of CAT5E or higher specifications be used for PoE power supply, and the power supply distance be within 100 m.
PoE Power Supply Negotiation Mechanism
In actual applications, PoE levels supported by PSEs (generally PoE switches or PoE adapters) and PDs (generally APs, network cameras, and IP phones) may vary depending on device brands and models. The actual power supply standards are determined through negotiation between PSEs and PDs.
After a PD is connected to a PSE through an Ethernet cable, they negotiate the power supply based on the following rules:
- PD detection: The PSE periodically transmits a low voltage (2.7 V to 10.1 V) through its interfaces in order to detect PDs. If a specific resistance ranging from 19 kΩ to 26.5 kΩ is detected, the cable is connected to a PD that supports PoE.
- Power negotiation: The PSE classifies the PD based on its power supply capability and negotiates the power to supply.The following negotiation methods are typically used:
- The PSE determines the current according to the class returned by the PD, classifies the PD, and determines the power to supply.
- Based on Link Layer Discovery Protocol (LLDP), the PSE and PD use the optional Power via MDI TLV field to discover and notify each other of their power supply capabilities.
- Power supply startup: The PSE starts to supply a low voltage to the PD within less than 15 μs (startup period), and then raises the power to the full 48 V DC voltage eventually.
- Normal power supply: After the voltage reaches 48 V, the PSE supplies stable and reliable 48 V DC power to the PD. The PoE power output to the PD does not exceed the maximum capacity of the PSE.
- Disconnection of power supply: The PSE keeps detecting the input current of the PD while supplying power. Upon detecting that the current of the PD falls below the minimum value or increases sharply, the PSE stops supplying power to the PD and re-initiates the PD detection process. This situation occurs when the PD is disconnected from the PSE, encounters a power overload or short circuit, or its power consumption exceeds the power supply capacity of the PSE.
On a WLAN, a PoE switch or PoE adapter is typically used as a PSE to supply power to APs. If a PoE adapter is used, it can transparently transmit LLDP data units (LLDPDUs) to APs. Therefore, power supply standard negotiation may still be affected by the switch on the network.
Understanding the Power Supply Downgrade of Huawei APs
What Is a Power Supply Downgrade?
During the WLAN deployment, APs are typically used as PDs and PoE switches or PoE adapters as PSEs to supply power to APs. Power supply standards required by APs vary depending on AP models. If the power received by an AP cannot reach the required level, service performance or functions of the AP may be affected (as listed in Table 1-2), or even the AP may go offline or restart.
Service Type |
Typical Symptom |
|---|---|
Wired services |
The PoE OUT function is unavailable. |
The output power of the USB port decreases or the USB port is unavailable. |
|
The IoT card slot is unavailable. |
|
Some network ports or RF ports are unavailable. |
|
A network port and an optical port work as combo ports. When one of them is working, the other is unavailable. |
|
The maximum network port rate decreases. |
|
Wireless services |
The number of spatial streams decreases. |
The maximum transmit power decreases. |
|
The maximum bandwidth supported decreases. |
|
Basic WLAN services are unavailable. |
When the basic WLAN services of an AP are available, as long as the PoE power supply negotiation result is consistent with the power supply capability of the PSE, the AP runs properly even if the power supply downgrade occurs. To maximize the AP service performance, it is recommended that PSEs supporting higher power supply standards be used within the project budget.
How Do I Check the Power Supply Downgrade Limit of an AP?
When the power supply is insufficient, the impact on the AP functions and performance varies depending on AP models.
- For Huawei AirEngine series APs (except the AirEngine 5760-10), check the power supply downgrade limit as follows:
Visit Info-Finder, select a product series, and view hardware specifications in the hardware center. You can check the power supply downgrade limits at different power supply levels.
- For Huawei Wi-Fi 5 series APs, AP7060DN, and AirEngine 5760-10, check the power supply downgrade limit as follows:
Check "AP PoE Information in Different Power Supply Standards (V200R019C00 or Earlier)" in Wireless Access Controller (AC and Fit AP) V200R019C00 Product Documentation.
How Do I Determine a Power Supply Downgrade of an AP?
If any of the following symptoms occurs, a power supply downgrade occurs on an AP:
- A message similar to the following is displayed when a user logs in to the AP:
Warning: The required power supply mode for the device is 802.3BT90. The current power supply is insufficient (Limited), and some functions are limited.
- Check AP information on the AC. The ExtraInfo field is displayed as P.
<HUAWEI> display ap all ... ---------------------------------------------------------------------------------------------------- ID MAC Name Group IP Type State STA Uptime ExtraInfo ---------------------------------------------------------------------------------------------------- 0 00e0-fcf6-76a0 area_1 ap-group1 192.168.120.254 AirEngine8760-X1-PRO nor 0 4H:49M:11S P ...
- The AP generates an alarm indicating that the power supply is insufficient.
Case 1:
WLAN/4/AP_POWER_LIMITED:OID[oid] The AP works in Limited mode due to insufficient power supply.
Case 2:
WLAN/2/POWER_INSUFF:OID [oid] AP power supply is insufficient.
The PoE adapter (part number: 02220154) supports the 802.3bt power supply standard. However, the 802.3at power supply standard is used by default. For AirEngine series APs that support 802.3bt, it is recommended that LLDP be disabled and the power force work-mode { bt60 | bt90 } command be executed to forcibly set the power supply standard to 802.3bt. This command is supported by ACs running V200R019C10 or later versions. For ACs running V200R019C00, install the V200R019C00SPH510 patch to support this command.
Common Methods for Locating Power Supply Downgrade Issues on Huawei APs
If a power supply downgrade occurs, perform the following steps to locate the issue:
- Check the current power supply level of the AP.
On the AC:
<HUAWEI> display ap power-workmode all ----------------------------------------------------------------------------------------------------------------------------------- ID MAC Name Group Power-workmode Decided by ----------------------------------------------------------------------------------------------------------------------------------- ... 3 00e0-fc76-e360 ap_1 default AT(Limited) LLDP ...
On the AP:
<AP> display current power-workmode Current power workmode is AT (Limited), decided by LLDP
The command output shows the PoE standard that is being used by the target AP, AP working status, and reason for the negotiation result.
Parameter
Description
PoE standard
- AF: 802.3af
- AT: 802.3at
- BT60: 802.3bt class 6
- BT90: 802.3bt class 8
Working status
- Normal or FULL: The AP is working properly, and no function is restricted.
- Limited or RESTRICTED: The power supply is insufficient. Basic WLAN services of the AP are available, but some functions are restricted.
- Insufficient: The power supply is severely insufficient, and basic WLAN services of the AP are unavailable.
NOTE:Upon the Limited, RESTRICTED, or Insufficient state, a power supply downgrade of the AP is determined.
Reason for the working mode
- LLDP: negotiated by LLDP
- Hardware detect: negotiated by hardware
- AP capability: determined by the highest capability of the AP
- Configuration: forcibly specified
- Check the PSE and ensure that its PoE capability meets the power supply requirements of the AP.
Note that the PoE output power supported by the switch on a specific network port is affected by the output power and the maximum power of the port. Evaluate the actual power supply capability of the corresponding network port based on the switch specifications and output power.
- Increase the power supply level within the range allowed by the live network.
- Case 1: The power supply standard of the AP is lower than that of the PSE.
If the PSE is a PoE switch, ensure that LLDP negotiation is enabled on the switch and the switch advertises correct Power via MDI TLV negotiation parameters.
If the PSE is a PoE adapter, ensure that LLDP negotiation is enabled on the switch directly connected to the AP and the switch advertises correct Power via MDI TLV negotiation parameters, because LLDP negotiation has a higher priority than hardware negotiation.
For example, GE0/0/3 on a Huawei PoE switch is used to provide 802.3at power for APs. Perform the following configurations:
<Switch> lldp enable <Switch> interface gigabitethernet 0/0/3 [Switch-GigabitEthernet0/0/3] lldp enable [Switch-GigabitEthernet0/0/3] lldp dot3-tlv power 802.3at
For AirEngine series APs (except the AirEngine 5760-10), you can directly disable LLDP negotiation on the AP and forcibly specify the power supply mode of the AP based on the power supply capability of the PSE.
<AC> system-view [AC] wlan [AC-wlan-view] port-link-profile name port-link1 //Assume that the AP wired port link profile port-link1 is bound to the target AP. [AC-wlan-port-link-prof-port-link1] undo lldp enable //Disable LLDP negotiation. [AC-wlan-port-link-prof-port-link1] quit [AC-wlan-view] ap-system-profile name ap-system1 //Assume that the AP system profile ap-system1 is bound to the target AP. [AC-wlan-ap-system-prof-ap-system1] power force work-mode bt90 //Configure the 802.3bt class 8 power supply standard. Warning: If the PSE does not reach the target power supply level, executing this command may cause the AP to repeatedly restart due to insufficient power. Continue? [Y/N]: y
If the manually specified AP power supply mode exceeds the actual capability of the PSE, the AP may restart repeatedly due to insufficient power supply. Specify the power supply mode for the AP based on the actual power supply capability of the PSE.
- Case 2: The power supply standard of the AP is the same as that of the PSE.
It is recommended that the PoE output power of the PSE be increased or the PSE be replaced with one that supports a higher PoE power supply level.
- Case 1: The power supply standard of the AP is lower than that of the PSE.
Typical Power Supply Downgrade Cases
An Alarm Indicating Insufficient Power Supply Is Generated
Symptom
On the NMS, the AirEngine 8760-X1-PRO generates an alarm indicating insufficient power supply.
WLAN/4/AP_POWER_LIMITED:OID[oid] The AP works in Limited mode due to insufficient power supply.
Location Method
- Log in to the AP in CLI mode and check the current power supply level of the AP.
<AP> display current power-workmode Current power workmode is AF (Insufficient), decided by LLDP
The command output shows that the target AP uses the 802.3af PoE standard through LLDP negotiation, which cannot meet the minimum requirements of basic WLAN services.
- Check the power supply capability of the PSE that supplies power to the AP.
Assume that the PSE is a Huawei PoE switch and GE0/0/3 is used to provide power for the AP.
<Switch> display poe power interface gigabitethernet 0/0/3 ... user set max power(mW) : 30000 //The maximum output power of the port is 30000 mW (supporting the 802.3at standard). ... <Switch> display poe power-state interface gigabitethernet 0/0/3 ... Power-up mode : af //The current PoE mode of the port is 802.3af. ...
The command output shows that the PoE switch supports the 802.3at standard, but the power supply standard in use is 802.3af.
- Check the power supply downgrade limit based on the AP model (AirEngine 8760-X1-PRO). The minimum power supply mode for the AP is 802.3at.
- Modify the service configuration so that the AP and PSE negotiate to use the 802.3at standard for power supply.
- Method 1: Enable LLDP negotiation on the switch and configure the 802.3 Power via MDI TLV advertised by GE0/0/3 to comply with 802.3at.
<Switch> system-view [Switch] lldp enable [Switch] interface gigabitethernet 0/0/3 [Switch-GigabitEthernet0/0/3] lldp enable [Switch-GigabitEthernet0/0/3] lldp dot3-tlv power 802.3at
- Method 2: Disable LLDP negotiation of the AP on the AC.
<AC> system-view [AC] wlan [AC-wlan-view] port-link-profile name default //Assume that the AP wired port link profile default is bound to the target AP. [AC-wlan-port-link-prof-default] undo lldp enable //Disable LLDP negotiation on all APs bound to the profile. [AC-wlan-port-link-prof-default] quit
Wait for 1 to 2 minutes, and check whether 802.3at can be negotiated through hardware.
If 802.3at cannot be negotiated for AirEngine series APs (except the AirEngine 5760-10), forcibly set the PoE power supply mode to 802.3at.
[AC-wlan-view] ap-system-profile name ap-system1 //Assume that the AP system profile ap-system1 is bound to the target AP. [AC-wlan-ap-system-prof-ap-system1] power force work-mode at //Configure the 802.3at mode for all APs bound to this profile. Warning: If the PSE does not reach the target power supply level, executing this command may cause the AP to repeatedly restart due to insufficient power. Continue? [Y/N]: y
- Method 1: Enable LLDP negotiation on the switch and configure the 802.3 Power via MDI TLV advertised by GE0/0/3 to comply with 802.3at.
Experience Summary
When the power supply for an AP is insufficient, no alarm is generated if only the number of spatial streams decreases. However, if certain functions are restricted, for example, the third radio does not work or an IoT device connected to the USB port is unavailable, an alarm indicating insufficient power supply is reported.
