Tag Archives: Cisco AIR 1140 Series

PoE-based access points Tx power level limitations

I recently noticed that Cisco AP 1142 Tx power level is not a constant value. It is dependent on a data rate in use.
Less words, here’s an example of “show controllers dot11Radio” taken from Cisco AIR-LAP1142N-E-K9:

interface Dot11Radio0
Radio AIR-AP1140G, Base Address b4a4.e3ca.f130, BBlock version 0.00, Software version 3.00.81
Serial number: <cut>
Number of supported simultaneous BSSID on Dot11Radio0: 16
Carrier Set: EMEA (EU) (-E)
Uniform Spreading Required: No
Configured Frequency: 2462 MHz Channel 11
Allowed Frequencies: 2412(1) 2417(2) 2422(3) 2427(4) 2432(5) 2437(6) 2442(7) 2447(8) 2452(9) 2457(10) 2462(11) 2467(12) 2472(13)
Listen Frequencies: 2412(1) 2417(2) 2422(3) 2427(4) 2432(5) 2437(6) 2442(7) 2447(8) 2452(9) 2457(10) 2462(11) 2467(12) 2472(13) 2484(14)
Beacon Flags: 0, Interface Flags 20105, Interface Events 0, Mode 9; Beacons are enabled; Probes are enabled
Configured Power: 17 dBm (level 1)
Active power levels by rate
1.0 to 11.0 , 16 dBm, changed due to regulatory maximum
6.0 to 48.0 , 13 dBm, changed due to regulatory maximum
54.0 to 54.0 , 11 dBm, changed due to regulatory maximum
6.0-bf to 54.0-b, 10 dBm, changed due to regulatory maximum
m0. to m5. , 13 dBm, changed due to regulatory maximum
m6. to m6. , 11 dBm, changed due to regulatory maximum
m7. to m7. , 10 dBm, changed due to regulatory maximum
m8. to m13. , 13 dBm, changed due to regulatory maximum
m14. to m14. , 11 dBm, changed due to regulatory maximum
m15. to m15. , 10 dBm, changed due to regulatory maximum
m0.-4 to m5.-4 , 13 dBm, changed due to regulatory maximum
m6.-4 to m6.-4 , 11 dBm, changed due to regulatory maximum
m7.-4 to m7.-4 , 10 dBm, changed due to regulatory maximum
m8.-4 to m13.-4, 13 dBm, changed due to regulatory maximum
m14.-4 to m14.-4, 11 dBm, changed due to regulatory maximum
m15.-4 to m15.-4, 10 dBm, changed due to regulatory maximum
6.0-d to 48.0-d, 13 dBm, changed due to regulatory maximum
54.0-d to 54.0-d, 11 dBm, changed due to regulatory maximum
OffChnl Power: 16, Rate 1.0
Allowed Power Levels: -1 2 5 8 11 14 17
Allowed Client Power Levels: 2 5 8 11 14 17

Why is it like this? Why higher data rates have lower Tx power levels? These were my questions too. Read more …

A correct way to shutdown Cisco Autonomous AP

An interesting fact – powered over Ethernet autonomous Cisco access point continue to associate clients even if you shutdown the relevant switch port! I recently shutdown the switch port to which a spare access point has been connected, assuming it will stop providing PoE. Few days later my friend’s IT specialist reported their customers have connectivity problems when they approach that particular access point. He also asked if the blue light reflects a working condition. That knocked me down. How could it be powered on if I administratively disabled the switch port?! Read more …