300-425 · Question #78
A technician connects a Cisco Aironet 3700 Series access point to a switch and realizes that the AP is coming up with 3x3 MIMO. Which reason explains this behavior?
The correct answer is B. The switch is 802.3af capable. The Cisco Aironet 3700 AP requires 802.3at (PoE+) power to operate at full 4x4 MIMO capacity; when connected to an 802.3af-only switch, the AP reduces its radio chains to 3x3 MIMO due to insufficient power delivery.
Question
A technician connects a Cisco Aironet 3700 Series access point to a switch and realizes that the AP is coming up with 3x3 MIMO. Which reason explains this behavior?
Options
- AA redundant power supply is unavailable on the switch.
- BThe switch is 802.3af capable.
- CThe AP is getting power from a power injector.
- DThe switch is PoE+ capable.
How the community answered
(15 responses)- B87% (13)
- C7% (1)
- D7% (1)
Why each option
The Cisco Aironet 3700 AP requires 802.3at (PoE+) power to operate at full 4x4 MIMO capacity; when connected to an 802.3af-only switch, the AP reduces its radio chains to 3x3 MIMO due to insufficient power delivery.
Redundant power supply availability on the switch is unrelated to the AP's MIMO configuration or radio chain count.
The Cisco Aironet 3700 Series supports 4x4:3 MIMO at full power but falls back to 3x3 MIMO when powered by an 802.3af switch, which delivers only up to 15.4W - insufficient for all four transmit chains. 802.3at (PoE+) provides up to 30W, which is required for full radio chain operation on this AP model.
A power injector typically supplies 802.3at (PoE+) levels, which would provide sufficient wattage for full 4x4 MIMO operation rather than causing a reduction.
If the switch were PoE+ (802.3at) capable and delivering full power, the AP would operate at 4x4 MIMO capacity, not fall back to 3x3.
Concept tested: PoE power budget impact on AP MIMO capability
Source: https://www.cisco.com/c/en/us/products/collateral/wireless/aironet-3700-series/data_sheet_c78-730593.html
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