Channels and Maximum Power Settings for Cisco 3700

The Tx Power Level Assignment for each AP shows its current power level assignment in a numbering system that starts with 1 and ends with 8. The number 1 indicates the AP is on full power and the higher the number goes less power are transmitted.

That number (1-8) can be converted to dBm or mW to show the AP’s actual power output by using this command ‘show ap config 802.11a’. It is here where you might notice the power level of APs all on power level 1 might not be transmitting the same dBm or mW.

The reason for this is the UNII band the AP is on for example below is an extraction of the ‘show ap config 802.11a’ command for three APs. All three AP’s were configured exactly the same except for Dynamic Channel Assignment (DCA) which put them on three different UNII bands.

UNII-1

Tx Power
Num Of Supported Power Levels …………. 3
Tx Power Level 1 …………………….. 8 dBm
Tx Power Level 2 …………………….. 5 dBm
Tx Power Level 3 …………………….. 2 dBm
Tx Power Configuration ……………….. AUTOMATIC
Current Tx Power Level ……………….. 1
Tx Power Assigned By …………………. DTPC
Phy OFDM parameters
Configuration ……………………….. AUTOMATIC
Current Channel ……………………… 36
Channel Assigned By ………………….. DCA

UNII-2Ext

Tx Power
Num Of Supported Power Levels …………. 5
Tx Power Level 1 …………………….. 16 dBm
Tx Power Level 2 …………………….. 13 dBm
Tx Power Level 3 …………………….. 10 dBm
Tx Power Level 4 …………………….. 7 dBm
Tx Power Level 5 …………………….. 4 dBm
Tx Power Configuration ……………….. AUTOMATIC
Current Tx Power Level ……………….. 1
Tx Power Assigned By …………………. DTPC
Phy OFDM parameters
Configuration ……………………….. AUTOMATIC
Current Channel ……………………… 100
Channel Assigned By ………………….. DCA

UNII-3

Tx Power
Num Of Supported Power Levels …………. 8
Tx Power Level 1 …………………….. 23 dBm
Tx Power Level 2 …………………….. 20 dBm
Tx Power Level 3 …………………….. 17 dBm
Tx Power Level 4 …………………….. 14 dBm
Tx Power Level 5 …………………….. 11 dBm
Tx Power Level 6 …………………….. 8 dBm
Tx Power Level 7 …………………….. 5 dBm
Tx Power Level 8 …………………….. 2 dBm
Tx Power Configuration ……………….. AUTOMATIC
Current Tx Power Level ……………….. 1
Tx Power Assigned By …………………. DTPC
Phy OFDM parameters
Configuration ……………………….. AUTOMATIC
Current Channel ……………………… 149
Channel Assigned By ………………….. DCA

All three APs indicate Power Level 1 on the Wireless LAN Controller but their actual power transmit power is:
AP1 = 8dBm
AP2 = 16dBm
AP3 = 23dBm

With this information available you might want to disable certain UNII-bands as the power output is not enough for the environment the APs are in.

Below is the path to get to the Cisco provided spreadsheet indicating what the power setting will be for your regulatory domain using certain antennas, configuration settings and certain UNII-bands.

http://www.cisco.com/c/en/us/support/wireless/aironet-3700i-access-point/model.html

Under Install and Upgrade Guides click on Detailed Channels and Maximum Power Settings for Cisco 3702e and 3702i Series Access Points.

 Have fun.

Translating mW, dBm, MHz and channels

Every so often I have to configure the Radio Transmit Power on an Access Point (AP) and it just happen that the wireless client transmit power is provided in milliwatt (mW) but I need to configure the APs transmit power to match that of the wireless client which need to be done in decibel-milliwatt (dBm). So let’s translate between the two.

The Radio Transmit Power setting determines the power level of the radio transmission. The default power setting is the highest transmit power allowed in your regulatory domain. Government regulations define the highest allowable power level for radio devices. This setting must conform to established standards for the country in which you use the device. The power settings may be in mW or in dBm depending on the particular radio that is being configured.

Definitions:

• Watt (W): a unit of power equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm.
• Milliwatt (mW): a unit of power equal to one thousandth of a watt.
• Decibel-milliwatt (dBm): an electrical power unit in decibels (dB), referenced to 1 milliwatt (mW).

Translation between mW and dBm:

mW	dBm
1	-1
2	2
3	5
4	6
5	7
6	8
8	9
10	10
12	11
15	12
20	13
25	14
30	15
40	16
50	17
60	18
80	19
100	20
125	21
150	22
200	23
250	24

Then there is the configuration of channels for your autonomous access point and instead of providing the channel number it actually asks for the corresponding frequency in your regulatory domain.

Each 2.4-GHz channel are 22 MHz wide. The bandwidth for channels 1, 6, and 11 does not overlap, so you can set up multiple access points in the same vicinity without causing interference. Both 802.11b and 802.11g 2.4-GHz radios use the same channels and frequencies.

The 5-GHz radio operates from 5180 to 5825 MHz. Each channel covers 20 MHz, and the bandwidth for the channels overlaps slightly. For best performance, use channels that are not adjacent (44 and 46, for example) for radios that are close to each other.

Translation between channel and MHz for 802.11b/g:

Channel Identifier	Center Frequency (MHz)
1	2412
2	2417
3	2422
4	2427
5	2432
6	2437
7	2442
8	2447
9	2452
10	2457
11	2462
12	2467
13	2472
14	2484

Translation between channel and MHz for 802.11a:

Channel ID	Center Frequency (MHz)
5150 to 5250 MHz
34	5170
36	5180
38	5190
40	5200
42	5210
44	5220
46	5230
48	5240
5250 to 5350 MHz
52	5260
56	5280
60	5300
64	5320
5470 to 5725 MHz
100	5500
104	5520
108	5540
112	5560
116	5580
120	5600
124	5620
128	5640
132	5660
136	5680
140	5700
5725 to 5850 MHz
149	5745
153	5765
157	5785
161	5805
165	5825

Reference                                                              http://www.cisco.com/c/en/us/td/docs/wireless/access_point/12-4-25d-JA/Configuration/guide/cg_12_4_25d_JA/scg12-4-25d-JA-chap6-radio.html

 http://www.cisco.com/web/techdoc/wireless/access_points/online_help/eag/123-02.JA/1400BR/h_ap_network-if_802-11_c.html

 http://www.cisco.com/c/en/us/td/docs/wireless/access_point/channels/ios/reference/guide/atonchp2/1200_chp.html#wp1047037