In buying the 2700's and the 3700's by Cisco, you're into the world of the 4x4 antenna AP. This AP can transmit and receive on all its antennas at once - meaning you can have multiple streams to provide that high throughput, as well as improved signal coverage over earlier models.
However, there's a major gotcha we found when first using these APs that's worth knowing about. The AP will power up with normal POE, but that last antenna has bumped up the power draw on the AP - now it's up at just a little over 16W, more than the 15.4W supplied by normal POE.
There's a bunch of PoE types - here's the quick run down:
Normal PoE 802.3af: Up to 15.4W
Cisco Enhanced PoE: Provides for up to 20w
802.3at: Uup to 30W (although the standard is strictly 25.5)
The big one! UPoE: Up to 60W
Cisco Switch Types: More POE Supports more Antennas
If you've got an older switch that can only do standard POE, no great shakes - the AP will power one antenna down and continue to operate. The drawback is fewer spacial streams and the AP won't provide as perfect and even coverage as it would have done with the extra antenna.
The answer is to use a newer switch. ePOE is the feature that you need to turn on in order to enable to the extra power - be careful though as the switch only has so much power available. The amount of APs you can support will depend on how large a PSU you bought with the switch.
Older switch = Less antennas
Newer switch = More antennas
Check with this command: show inline-power
Enable Cisco enhanced POE (ePOE)
Quick drumroll...... how do you enable the extra power you need?
Firstly you need a switch that can support ePOE, such as the Cisco 3560E or the Cisco 3750E switches. To enable power up to 20W on the switchport, use the interface specific command below:
power inline port maximum 20000
You might well run into the issue that the command is not appearing. Most likely in this case, you have an older IOS - although it's been supported for quite a long time. The command was enabled back in 2008 from IOS 12.2(44)SE.
Checking ePOE is working
The screen shot below shows how to check the AP is running at full power. Access the WLC GUI and go to the following menu:
Wireless > Access Points > Select the AP of interest
Click on the Advanced tab
The item to check is highlighted in the screen shot below - should show 'full power' when all antennas are operational.
You can also check on the switch, by issuing the show inline-power command to see the power draw on each port:
Cisco's enhanced Power Over Ethernet needs to be used when you are using 2700's or 3700's in your solution. Without using the correct level of available POE, the APs tend to shut down an antenna, which does allow them to continue to operate, but will likely effect the coverage the AP can provide.
In conclusion - the APs now use more power than they used to, so you may find yourself needing a switch upgrade when upgrading your APs.