Tx Power Level is an important variable that, in combination with antenna gain, influences coverage patterns. Cisco wireless controller dynamically adjusts transmit power levels according to current RF conditions, access point’s capabilities and local regulatory domain recommendations, that may vary per band and/or channel. We, as an engineers, should be capable to confirm current Tx Power level, list of all supported Tx Power levels and antenna gain (if applicable). No coverage or heatmap approximations can be made without this information. With this post I will provide a number of different useful CLI commands that may be used to quickly find Tx Power levels information per-AP and in bulk.
Different regulatory domains vary in their recommendations as to what channels can be used by 802.11 standard devices and maximum EIRP (Effective Isotropic Radiation Power) levels, which consists of maximum Tx Power and max antenna gain. The following table show FCC limitations in 2.4GHz range only for your reference (applicable to USA, Canada and some South America countries).
| 2.4GHz Point-to-Multipoint | |||
| Max Tx Power | Max Antenna Gain (dBi) | Max EIRP (dBm) | Max EIGRP (Watts) |
| 30 dBm or 1 W | 6 | 36 | 4 |
| 27 dBm or 500 mW | 9 | 36 | 4 |
| 24 dBm or 250 mW | 12 | 36 | 4 |
| 21 dBm or 125 mW | 15 | 36 | 4 |
| 18 dBm or 62 mW | 18 | 36 | 4 |
| 15 dBm or 31 mW | 21 | 36 | 4 |
| 12 dBm or 16 mW | 24 | 36 | 4 |
Note: It is possible to increase antenna gain at expense of Tx Power. For each dBm subtracted from Tx Power, one dBi can be added to antenna gain.
| 2.4GHz Point-to-Point | |||
| Max Tx Power | Max Antenna Gain (dBi) | Max EIRP (dBm) | Max EIGRP (Watts) |
| 30 dBm or 1 W | 6 | 36 | 4 |
| 29 dBm or 800 mW | 9 | 38 | 6.3 |
| 28 dBm or 630 mW | 12 | 40 | 10 |
| 27 dBm or 500 mW | 15 | 42 | 16 |
| 26 dBm or 400 mW | 18 | 44 | 25 |
| 25 dBm or 316 mW | 21 | 46 | 39.8 |
| 24 dBm or 250 mW | 24 | 48 | 63 |
| 23 dBm or 200 mW | 27 | 50 | 100 |
| 22 dBm or 160 mW | 30 | 52 | 158 |
Note: As opposed to the Point-to-Multipoint rules, for each dBm subtracted from Tx Power, three (3) dBi can be added to the antenna gain.
Surprisingly, Cisco does not refer to dBm values on its controllers and access points, instead a number of transmit power levels represent different amount of actual transmit power, where Level 1 stands for max possible Tx Power. The following output examples show supported 802.11a Tx Power levels and corresponding Tx Power amount in dBm for different access point models and regulatory domains.
Europe / Cisco 1242AG-E Tx Power Num Of Supported Power Levels ............. 8 Tx Power Level 1 .......................... 17 dBm Tx Power Level 2 .......................... 15 dBm Tx Power Level 3 .......................... 14 dBm Tx Power Level 4 .......................... 11 dBm Tx Power Level 5 .......................... 8 dBm Tx Power Level 6 .......................... 5 dBm Tx Power Level 7 .......................... 2 dBm Tx Power Level 8 .......................... -1 dBm Current Tx Power Level .................... 1 External Antenna Gain (in .5 dBi units).... 7
Europe / Cisco 1142N-E Tx Power Num Of Supported Power Levels ............. 7 Tx Power Level 1 .......................... 17 dBm Tx Power Level 2 .......................... 14 dBm Tx Power Level 3 .......................... 11 dBm Tx Power Level 4 .......................... 8 dBm Tx Power Level 5 .......................... 5 dBm Tx Power Level 6 .......................... 2 dBm Tx Power Level 7 .......................... -1 dBm Current Tx Power Level .................... 1 Internal Antenna Gain (in .5 dBi units).... 8
Ukraine / Cisco 2602I-E Tx Power Num Of Supported Power Levels ............. 5 Tx Power Level 1 .......................... 18 dBm Tx Power Level 2 .......................... 15 dBm Tx Power Level 3 .......................... 12 dBm Tx Power Level 4 .......................... 9 dBm Tx Power Level 5 .......................... 6 dBm Current Tx Power Level .................... 1 Internal Antenna Gain (in .5 dBi units).... 8
Australia / Cisco 1142N-N Tx Power Num Of Supported Power Levels ............. 6 Tx Power Level 1 .......................... 14 dBm Tx Power Level 2 .......................... 11 dBm Tx Power Level 3 .......................... 8 dBm Tx Power Level 4 .......................... 5 dBm Tx Power Level 5 .......................... 2 dBm Tx Power Level 6 .......................... -1 dBm Current Tx Power Level .................... 1 Internal Antenna Gain (in .5 dBi units).... 8
These outputs were taken directly from the controllers by using the following very useful command:
show ap config 802.11a ap-name
show ap config 802.11b ap-name
This command also displays a lot of different information about a particular access point, such as supported and current channels, model, software version, supported rates, mode and other. Unfortunately, old versions of AireOS do not support output filtering, like in Cisco IOS (include, exclude). You have to scroll quite a few pages before Tx Power information appears on the screen. Recent versions (starting from 7.5) have grep feature implemented. It can be used at our advantage to minimize the displayed output to only show Tx Power related information, such as shown in my outputs. The full modified command is the following
grep include “Tx Power|Gain” “show ap config 802.11a ap-name“
To show summary information that includes the whole range of access points that are registered on the controller and their current channels and Tx power levels the following commands may be useful.
show advanced 802.11a txpower
show advanced 802.11b txpower
The output of this command is AireOS version dependent. Earlier versions of AireOS only provide Tx Power Control (TPC) algorithm configuration, such as shown below:
(Cisco Controller) >show advanced 802.11a txpower Automatic Transmit Power Assignment Transmit Power Assignment Mode................. AUTO Transmit Power Update Interval................. 600 seconds Transmit Power Threshold....................... -70 dBm Transmit Power Neighbor Count.................. 3 APs Min Transmit Power............................. -10 dBm Max Transmit Power............................. 30 dBm Transmit Power Update Contribution............. SNI.. Transmit Power Assignment Leader............... CONTROLLER-1 (10.10.10.10) Last Run....................................... 201 seconds ago
Recent versions provide significantly more information, that includes the list of all access points, their supported Tx Power Levels (in dBm) and current channel and Tx Power level configuration:
(Cisco Controller) >show advanced 802.11a txpower Leader Automatic Transmit Power Assignment Transmit Power Assignment Mode................. AUTO Transmit Power Update Interval................. 600 seconds Transmit Power Threshold....................... -70 dBm Transmit Power Neighbor Count.................. 3 APs Min Transmit Power............................. -10 dBm Max Transmit Power............................. 30 dBm Update Contribution Noise........................................ Enable Interference................................. Enable Load......................................... Disable Device Aware................................. Disable Transmit Power Assignment Leader............... CONTROLLER-2 (10.10.10.20) Last Run....................................... 414 seconds ago Last Run Time.................................. 0 seconds TPC Mode....................................... Version 1 TPCv2 Target RSSI.............................. -67 dBm TPCv2 VoWLAN Guide RSSI........................ -67.0 dBm TPCv2 SOP...................................... -85.0 dBm TPCv2 Default Client Ant Gain.................. 0.0 dBi TPCv2 Path Loss Decay Factor................... 3.6 TPCv2 Search Intensity......................... 10 Iterations AP Name Channel TxPower Allowed Power Levels -------------------------------- ---------- ------------- ------------------------ AP-1 *40 *1/5 (18 dBm) [18/15/12/9/6/6/6/6] AP-2 *36 *1/5 (18 dBm) [18/15/12/9/6/6/6/6] AP-3 *44 *2/5 (15 dBm) [18/15/12/9/6/6/6/6]
Note: 1/5 TxPower means that current Tx Power level is 1 out of 5 total. In turn, Allowed Power Levels column lists all possible Tx Power levels in dBm, where Level 1 is represented by the leftmost value, or 18 dBm in our example. Even though 8 different values are shown, only 5 leftmost are significant (that is, access points support only 5 different levels). The rest must be ignored.
Another command that may be useful finding Tx Power information for all access points in one go is
show advanced 802.11a summary
show advanced 802.11b summary
It shows brief information about all connected access points and their operational state for the specific band, including channel in use and current Tx Power level. Apart from Tx Power Level, recent versions of AireOS also show a real Tx Power amount in dBm. Older versions of AireOS show Tx Power Level only and no any values in dBm. Therefore engineer must be aware what dBm values correspond to shown levels.
WLC 4402 using 7.0.250.0 code:
(Cisco Controller) >show advanced 802.11a summary AP Name MAC Address Admin State Operation State Channel TxPower -------------------------------- ------------------ ------------ ----- Kyiv-1 6c:9c:ed:b5:a4:d0 ENABLED UP 64* 1(*)
WLC 5508 using 7.5.102.0 code:
(Cisco Controller) >show advanced 802.11a summary Member RRM Information AP Name MAC Address Slot Admin Oper Channel TxPower -------------------------------- ----------------- ---- -------- AP-1 f4:1f:c2:e7:a1:80 1 ENABLED UP 40* *1/5 (18 dBm) AP-2 0c:27:24:0f:7f:30 1 ENABLED UP 36* *1/5 (18 dBm) AP-3 f4:1f:c2:5b:a4:b0 1 ENABLED UP 44* *2/5 (15 dBm)
Hope you find this useful.
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