802.11n is comprised of multiple Transmit (Tx) and Multiple Receive (Rx) "chains". Commonly you see this abbreviated as 2x2 or 3x3.
The first number in the specification sheet is the aggregate of all Tx chains, whereas the second number is 'per chain'.
Note on the AP-115 we have the following information on the datasheet:
"The AP-115 and IAP-115 APs feature a 2.4-GHz and a 5-GHz radio, each with 3x3:3 MIMO and three integrated omni-directional downtilt antennas."
So that means 3 Tx chains for our AP-115.
Most 802.11n products are specified in this methodology today xx dBm per chain and yy dBm total/aggregate power in each band.
JF