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With great power comes great Wi-Fi – PoE for Wi-Fi 6 and 6E

David Coleman Director, Wireless Networking at the Office of the CTO Published 16 Dec 2021

Whenever I talk about Wi-Fi, I always try to remind everyone that Wi-Fi is an access technology that operates at layers one and two of the OSI model. And the purpose of enterprise-grade Wi-Fi is to provide seamless mobility and frictionless access for users and devices to corporate network assets. Typically, an access point (AP) is a wireless portal to a wired network infrastructure. As a result, there is always higher layer (3-7) design considerations and wired network discussions.

The most important conversation about wired network integration with Wi-Fi 6 and 6E APs is Power over Ethernet (PoE) requirements. And the most common question is, “Will these APs work with standard 802.3af PoE?” Enterprise Wi-Fi manufacturers have added more radio chains to their Wi-Fi 6 APs. Many of the current Wi-Fi 6 APs are dual-band 4×4:4 APs, and there are even 8×8:8 APs. Wi-Fi 6 APs also require much more processing power than previous generations of enterprise APs. The extra radio chains and processor capabilities require more power. The 15.4 watts (W) provided per port by standard 802.11af PoE is not adequate for 4×4:4 APs, and therefore 802.3at (PoE Plus) power is necessary. PoE Plus-capable switches can provide up to 30 watts of power per Ethernet port. PoE Plus-powered ports for 4×4:4 APs should be considered a standard requirement.

In most cases, standard PoE of 15.4 watts will be sufficient to power dual-band 2×2:2 Wi-Fi 6 APs. However, Wi-Fi 6E brings us tri-frequency capabilities. So, 15.4 watts (W) is inadequate for three 2×2:2 radios housed in the same AP. Therefore, 802.3at (PoE Plus) power is a necessary minimum for pretty much all Wi-Fi 6E AP form factors.

But what about 4×4:4 Wi-Fi 6E APs? Again, these will be tri-frequency with many radio chains. When these higher-end Wi-Fi 6E APs hit the market in 2023, as much as 45 watts will be needed to power 4×4:4 tri-frequency APs with full functionality. So now 802.3bt power is necessary because 802.3at is no longer sufficient. 802.3bt is the most current PoE standard that defines per-port power-source capabilities of 45 watts, 60 watts, 75 watts, and even 90 watts. Luckily, enterprise manufacturers now sell switches that support 802.3bt. But there is a cost involved.

What about downgrade PoE functionality in APs?

Unfortunately, at some point in time an AP may be connected to a PoE-enabled Ethernet port that is not able to provide the AP with the power it requires. This could occur because the AP is plugged into a port that provides older, less powerful PoE, such as a 4×4:4 AP being plugged into an 802.3af-enabled PoE port instead of an 802.3at or 802.3bt PoE port. Or there simply is not enough power budget.

Many of the enterprise WLAN vendors have incorporated various downgrade functions into their APs to deal with this problem. One method is to downgrade the MIMO capability of the AP. Since 5 GHz communications is typically more important than 2.4 GHz communications, decreasing the number of radio chains of the 2.4 GHz radio to 1×1:1 is one method of decreasing the AP power requirements. A vendor may also decrease the number of radio chains on the 5 GHz radio. And now, with Wi-Fi 6E APs, reduce the number of chains on the 6 GHz radio. If the AP has multiple Ethernet ports, another power-saving technique is to disable all of the additional Ethernet ports, leaving only the uplink Ethernet port as active. Other networking interfaces, such as a Bluetooth Low Energy (BLE) radio, may also be disabled to reduce power draw.

The point is that not all downgrade capabilities are created equal. A vendor might sell you 4×4:4 Wi-Fi 6E APs that will still operate on 25 Watts of 802.3at power; however, all three radios downgrade to 2×2:2. They needed 802.3bt power for full Wi-Fi functionality. Another vendor might figure out a way to still provide full tri-frequency functionality for all three Wi-Fi radios but disable some other function of the AP, such as a USB port. Always check and understand the amount of power needed for full AP functionality. If you are willing to accept some downgrade capabilities, make sure you know what gets turned off. I prefer the methods that maintain full Wi-Fi functionality but downgrade some other capability unrelated to the operation of the Wi-Fi radios.

It’s all about the power budget

Because many devices such as 802.11 APs, video cameras, and desktop VoIP phones may require power, situations can arise where there simply is not enough available wattage to power all the PoE ports. Network engineers have begun to realize the need for and importance of a power budget. Careful planning is needed to ensure that enough power is available for all the powered devices.

Enterprise switch vendors will list the PoE power budget within the switch specification sheet. The PoE power budget listed in a spec sheet is the amount of power available to the ports and is not earmarked for other switch functions. When reading the power budget specifications of a switch, be sure to determine how many ports are PoE- capable. For example, a switch vendor might offer various power supply and budget options for the same model 48-port switch. While a total power budget of 1440W would be enough to provide 803.3at power to 48 ports, the less expensive options of 480W or 845W could only provide PoE-Plus level power to 16 or 28 APs, respectively. Keep in mind that the larger the power budget, the more the cost of the PoE-enabled switch increases.

Ultimately, it is essential to plan your network with the proper PoE capabilities so that your devices receive the power needed, allowing them to operate at their optimal capabilities so that the network performs as it was designed. The power budget of a switch or multiple switches should be monitored to ensure that all devices can maintain power. Active budget information can usually be seen from the command line of a switch, the GUI interface, or monitored by a centralized cloud management solution.

An upgrade to most Wi-Fi 6E APs will at the very least require a recalculation of PoE power budgets. As Wi-Fi vendors add more radio chains, dual-band radios, and now tri-band radios, PoE power budget management will be of even greater importance moving forward.

Why are my APs rebooting?

Enterprise Wi-Fi vendors commonly receive support calls from customers complaining that APs randomly begin to reboot all of a sudden. Faulty cables or cabling exceeding 100 meters might result in insufficient or erratic power and cause an AP to reboot. However, in most cases, the root cause of random rebooting of APs is that the switch power budget has been eclipsed. Very often, if an AP cannot get the power that it needs, the AP will reboot and try again. Remember that other devices, such as desktop VoIP phones, also use PoE. An extra PoE-powered device has been plugged into a switch port, and now the power budget is insufficient. Or maybe there just is not enough power for the high-performance APs. Proper power budgeting for access points and any other PoE-capable devices is paramount.

Businesses may need to upgrade their switches to meet power budget needs if they deploy dual-band 4×4:4 Wi-Fi 6 APs or tri-radio Wi-Fi 6E APs. There is a good chance that most enterprise businesses already have access switches with 802.3at (PoE Plus) capabilities. But do existing switches have the necessary power budget for a 1:1 replacement for all the APs that require PoE Plus or even 802.3bt? I am worried that many businesses will suddenly be exceeding the overall power budgets of the switches. Nobody wants APs that randomly reboot, which negatively impacts the Wi-Fi user experience.

Conclusion:

Wired network integration is a very important yet often overlooked element of wireless network infrastructure upgrades. Bottom line, when discussing upgrading to Wi-Fi 6 or even better Wi-Fi 6E APs, you absolutely need to discuss the wired network integration and ensure all your APs have sufficient power. Now might also be a good time for a switch upgrade.

Portions of this blog have been excerpted from the free eBook:

Wi-Fi 6 & 6E for Dummies

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