The 9971 and 9951-series phones are class 4 (802.3at) rated, which means they will/can require more than 15.4w for operation. My question - if they are connected to a PoE port that can only provide class 3 (802.3af) power, will you be still be able to place audio calls? Basically, is the 802.3at-level power only required when making video calls?
From Kirk @ Cisco BU
4) Power is listed as 802.3af and 802.3at support. Are there any limitations when using 802.3af instead of 802.3at? I am guessing the USB ports may require the Class 4 PoE?
If using 802.3af power and wish to take advantage of the Cisco Unified IP Color Key Expansion Module for expansion of line/feature appearances, then power cube 4 power supply (supporting the IP Phone) is required to support the module or modules (actual number of modules is phone model dependent). Also note that 802.3af supports up to 15.4W of power to a given device and the classification of the power consumption is static and cannot be renegotiated later on. The AT specification allows power consumption up to 25W PLUS the ability to change power consumption after the initial classification.
From this excellent thread;
Thanks for the feedback, Rob - I've been through the referenced thread, and one thing still isn't perfectly clear.
One response indicates that the video call functionality is supported using only 802.3af (so, the power brick would only be required if going Wi-fi or if using the KEM. So what remains unclear is why the 9971 would ever require 802.3at (and NOT require a power cube). All I can see so far is that it will operate fine (audio/video) with standard power - anything beyond would require a cube.
Hope that makes sense, and thanks!