It’s become common place for wireless infrastructure vendors to state that their Access Points are “802.3af compatible” or have an 802.3af mode of operation, but this ‘compatible’ mode may not be what you expect. Be careful to read the small print across vendors, there are a number of shortcuts that can be taken to reduce power consumption:
- Reduced Transmit power: This is the simplest to limit, however depending on your deployment any limits here may adversely impact your coverage and your vendor’s auto-mitigation mechanisms.
- Reduced Transmit chains: Your 3x3 AP might only behave as a 2x3 or even 1x3 AP when running off 802.3af, and this may be dynamically limited based on data rates. The reason for this is that every transmit chain takes power, and a quick and easy way to reduce an AP’s overall power consumption is to limit how many transmit chains are active.
- Reduced Processing power: Down clocking the AP’s processor is another easy way to gain a bit of power margin. Look out for this as 802.11ac throughputs usually need a processor running at peak efficiency, in a lower power mode it may become a bottleneck on your system.
Rather than be surprised after the fact, ask your vendor for specifics on their 802.3af support. Note that what is changed and in what way may even vary model to model from the same vendor. That 3x3, 20dB transmit power AP you’re looking to buy may just become a 2x2 15dB AP by the time it’s up and running.