Cisco 3900 Series, 2900 Series, and 1900 Series Software Configuration Guide
Configuring the Radio
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Table Of Contents

Configuring Radio Settings

Enabling the Radio Interface

Configuring the Role in the Radio Network

Configuring Dual-Radio Fallback

Radio Tracking

Fast Ethernet Tracking

MAC-Address Tracking

Configuring Radio Data Rates

Configuring MCS Rates

Configuring Radio Transmit Power

Limiting the Power Level for Associated Client Devices

Configuring Radio Channel Settings

802.11n Channel Widths

Dynamic Frequency Selection

CLI Commands

Confirming that DFS is Enabled

Configuring a Channel

Blocking Channels from DFS Selection

Simulating Radar Detection

Setting the 802.11n Guard Interval

Enabling and Disabling World Mode

Disabling and Enabling Short Radio Preambles

Configuring Transmit and Receive Antennas

Enabling and Disabling Gratuitous Probe Response

Disabling and Enabling Aironet Extensions

Configuring the Ethernet Encapsulation Transformation Method

Enabling and Disabling Public Secure Packet Forwarding

Configuring Protected Ports

Configuring the Beacon Period and the DTIM

Configure RTS Threshold and Retries

Configuring the Maximum Data Retries

Configuring the Fragmentation Threshold

Enabling Short Slot Time for 802.11g Radios

Performing a Carrier Busy Test

Configuring VoIP Packet Handling


Configuring Radio Settings


The following sections describe how to configure radio settings for the wireless device:

Enabling the Radio Interface

Configuring the Role in the Radio Network

Configuring Dual-Radio Fallback

Configuring Radio Data Rates

Configuring MCS Rates

Configuring Radio Transmit Power

Configuring Radio Channel Settings

Enabling and Disabling World Mode

Disabling and Enabling Short Radio Preambles

Configuring Transmit and Receive Antennas

Enabling and Disabling Gratuitous Probe Response

Configuring the Ethernet Encapsulation Transformation Method

Enabling and Disabling Public Secure Packet Forwarding

Configuring the Beacon Period and the DTIM

Configure RTS Threshold and Retries

Configuring the Maximum Data Retries

Configuring the Fragmentation Threshold

Enabling Short Slot Time for 802.11g Radios

Performing a Carrier Busy Test

Configuring VoIP Packet Handling

Enabling the Radio Interface

The wireless device radios are disabled by default.


Note You must create a service set identifier (SSID) before you can enable the radio interface.


To enable the access point radio, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. dot11 ssid ssid

3. interface dot11radio {0| 1}

4. ssid ssid

5. no shutdown

6. end

7. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

dot11 ssid ssid

Enters the SSID. The SSID consists of up to 32 alphanumeric characters. SSIDs are case sensitive.

Step 3 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface.The 2.4-GHz and 802.11g/n 2.4-GHz radios are radio 0.

The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 4 

ssid ssid

Assigns the SSID that you created in Step 2 to the appropriate radio interface.

Step 5 

no shutdown

Enables the radio port.

Step 6 

end

Returns to privileged EXEC mode.

Step 7 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the shutdown command to disable the radio port.

Configuring the Role in the Radio Network

The radio performs the following roles in the wireless network:

Access point

Access point (fallback to radio shutdown)

Root bridge

Non-root bridge

Root bridge with wireless clients

Non-root bridge without wireless clients

You can also configure a fallback role for root access points. The wireless device automatically assumes the fallback role when its Ethernet port is disabled or disconnected from the wired LAN. The default fallback role for Cisco ISR wireless devices is as follows:

Shutdown—the wireless device shuts down its radio and disassociates all client devices.

To set the wireless device's radio network role and fallback role, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. station-role

4. non-root {bridge | wireless-clients}
root {access-point | ap-only | [bridge | wireless-clients] | [fallback | repeater | shutdown]}

5. workgroup-bridge {multicast | mode <client | infrastructure>| universal <Ethernet client MAC address>}

6. end

7. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface.

The 2.4-GHz and 802.11g/n 2.4-GHz radios are radio 0.

The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 3 

station-role

non-root
{bridge | wireless-clients}


root
{access-point | ap-only | [bridge | wireless-clients] | [fallback | repeater | shutdown]}



workgroup-bridge
{multicast | mode <client | infrastructure>| universal <Ethernet client MAC address>}

Sets the wireless device role.

Set the role to non-root bridge with or without wireless clients, to root access point or bridge, or to workgroup bridge.

Note The bridge mode radio supports point-to-point configuration only.

Note The repeater and wireless-clients commands are not supported on Cisco 1941-W Integrated Services Routers.

Note The scanner command is not supported on 1941-W Integrated Services Routers.

The Ethernet port is shut down when any one of the radios is configured as a repeater. Only one radio per access point may be configured as a workgroup bridge or repeater. A workgroup bridge can have a maximum of 25 clients, presuming that no other wireless clients are associated to the root bridge or access point.

 

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.


Note When you enable the role of a device in the radio network as a bridge/workgroup bridge and enable the interface using the no shut command, the physical status and the software status of the interface will be up (ready) only if the device on the other end (access point or bridge) is up. Otherwise, only the physical status of the device will be up. The software status will be up when the device on the other end is configured and ready.


Configuring Dual-Radio Fallback

The dual-radio fallback feature, see Figure 1, allows you to configure access points so that if the non-root bridge link connecting the access point to the network infrastructure goes down, the root access point link through which a client connects to the access point shut down. Shutting down the root access point link causes the client to roam to another access point. Without this feature, the client remains connected to the access point, but won't be able to send or receive data from the network.

Figure 1 Dual-Radio Fallback


Note This feature does not affect the fallback feature for single-radio access points.


You can configure dual-radio fallback in three ways:

Radio tracking

Fast Ethernet tracking

MAC-address tracking

Radio Tracking

You can configure the access point to track or monitor the status of one of its radios. If the tracked radio goes down or is disabled, the access point shuts down the other radio. If the tracked radio comes up, the access point enables the other radio.

To track radio 0, enter the following command:

# station-role root access-point fallback track d0 shutdown
 
 

To track radio 1, enter the following command:

# station-role root access-point fallback track d1 shutdown
 
 

Fast Ethernet Tracking

You can configure the access point for fallback when its Ethernet port is disabled or disconnected from the wired LAN. You configure the access point for Fast Ethernet tracking as described in the "Configuring the Role in the Radio Network" section.


Note Fast Ethernet tracking does not support the repeater mode.


To configure the access point for Fast Ethernet tracking, enter the following command:

# station-role root access-point fallback track fa 0

MAC-Address Tracking

You can configure the radio, whose role is root access point, to come up or go down by tracking a client access point, and using its MAC address on another radio. If the client disassociates from the access point, the root access point radio goes down. If the client reassociates with the access point, the root access point radio comes back up.

MAC-address tracking is most useful when the client is a non-root bridge access point connected to an upstream wired network.

For example, to track a client whose MAC address is 12:12:12:12:12:12, enter the following command:

# station-role root access-point fallback track mac-address 12:12:12:12:12:12 shutdown

Configuring Radio Data Rates

You use the data rate settings to choose the data rates that the wireless device uses for data transmission. The rates are expressed in megabits per second (Mb/s). The wireless device always attempts to transmit at the highest data rate set to basic, also known as required on the browser-based interface. If there are obstacles or interference, the wireless device steps down to the highest rate that allows data transmission. You can set each data rate to one of three states:

Basic (the GUI labels Basic rates as Required)—Allows transmission at this rate for all packets, both unicast and multicast. At least one of the wireless device's data rates must be set to basic.

Enabled—The wireless device transmits only unicast packets at this rate; multicast packets are sent at one of the data rates set to basic.

Disabled—The wireless device does not transmit data at this rate.


Note At least one data rate must be set to basic.


You can use the data rate settings to set an access point to serve client devices operating at specific data rates. For example, to set the 2.4-GHz radio for 11 Mb/s service only, set the 11-Mb/s rate to basic, and set the other data rates to disabled. To set the wireless device to serve only client devices operating at 1 and 2 Mb/s, set 1 and 2 to basic, and set the rest of the data rates to disabled. To set the 2.4-GHz, 802.11g radio to serve only 802.11g client devices, set any orthogonal frequency division multiplexing (OFDM) data rate (6, 9, 12, 18, 24, 36, 48, 54) to basic. To set the 5-GHz radio for 54-Mb/s service only, set the 54-Mb/s rate to basic, and set the other data rates to disabled.

You can configure the wireless device to set the data rates automatically to optimize either the range or the throughput. When you enter range for the data rate setting, the wireless device sets the 1-Mb/s rate to basic and sets the other rates to enabled.

The range setting allows the access point to extend the coverage area by compromising on the data rate. Therefore, if you have a client that cannot connect to the access point while other clients can, the client might not be within the coverage area of the access point. In such a case, using the range option will help extend the coverage area, and the client may be able to connect to the access point. Typically the trade-off is between throughput and range.

When the signal degrades (possibly due to distance from the access point), the rates renegotiate in order to maintain the link (but at a lower data rate). A link that is configured for a higher throughput simply drops when the signal degrades enough that it no longer sustains a configured high data rate, or the link roams to another access point with sufficient coverage, if one is available.

The balance between the two (throughput vs. range) is a design decision that must be made based on resources available to the wireless project, the type of traffic the users will be passing, the service level desired, and as always, the quality of the RF environment.When you enter throughput for the data rate setting, the wireless device sets all four data rates to basic.


Note When a wireless network has a mixed environment of 802.11b clients and 802.11g clients, make sure that data rates 1, 2, 5.5, and 11 Mb/s are set to required (basic) and that all other data rates are set to enable. The 802.11b adapters do not recognize the 54 Mb/s data rate and do not operate if data rates higher than 11 Mb/s are set to required on the connecting access point.


To configure the radio data rates, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0 | 1}

3. speed parameters

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0 | 1}

Enters interface configuration mode for the radio interface. The 2.4-GHz and the 802.11g/n 2.4-GHz radios are radio 0.

The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 3 

speed

802.11b, 2.4-GHz radio:

{[1.0] [11.0] [2.0] [5.5] [basic-1.0] [basic-11.0] [basic-2.0] [basic-5.5] | range | throughput}

802.11g, 2.4-GHz radio:

{[1.0] [2.0] [5.5] [6.0] [9.0] [11.0] [12.0] [18.0] [24.0] [36.0] [48.0] [54.0] [basic-1.0] [basic-2.0] [basic-5.5] [basic-6.0] [basic-9.0] [basic-11.0] [basic-12.0] [basic-18.0] [basic-24.0] [basic-36.0] [basic-48.0] [basic-54.0] | range |
throughput [ofdm] | default}

802.11a 5-GHz radio:

{[6.0] [9.0] [12.0] [18.0] [24.0] [36.0] [48.0] [54.0] [basic-6.0] [basic-9.0] [basic-12.0] [basic-18.0] [basic-24.0] [basic-36.0] [basic-48.0] [basic-54.0] |
range | throughput | ofdm-throughput | default}

802.11n 2.4-GHz radio:

{[1.0] [11.0] [12.0] [18.0] [2.0] [24.0] [36.0] [48.0] [5.5] [54.0] [6.0] [9.0] [basic-1.0] [basic-11.0] [basic-12.0] [basic-18.0] [basic-24.0] [basic-36.0] [basic-48.0] [basic-5.5] [basic-54.0] [basic-6.0] [basic-9.0] [default] [m0-7] [m0.] [m1.] [m10.] [m11.] [m12.] [m13.] [m14.] [m15.] [m2.] [m3.] [m4.] [m5.] [m6.] [m7.] [m8-15] [m8.] [m9.] [ofdm] [only-ofdm] | range | throughput}

802.11n 5-GHz radio:

{[12.0] [18.0] [24.0] [36.0] [48.0] [54.0] [6.0] [9.0] [basic-12.0] [basic-18.0] [basic-24.0] [basic-36.0] [basic-48.0] [basic-54.0] [basic-6.0] [basic-9.0] [default] [m0-7] [m0.] [m1.] [m10.] [m11.] [m12.] [m13.] [m14.] [m15.] [m2.] [m3.] [m4.] [m5.] [m6.] [m7.] [m8-15] [m8.] [m9.] | range | throughput}

Sets each data rate to basic or enabled, or enters range to optimize range or enters throughput to optimize throughput.

(Optional) Enter 1.0, 2.0, 5.5, and 11.0 to set these data rates to enabled on the 802.11b, 2.4-GHz radio.

Enter 1.0, 2.0, 5.5, 6.0, 9.0, 11.0, 12.0, 18.0, 24.0, 36.0, 48.0, and 54.0 to set these data rates to enabled on the 802.11g, 2.4-GHz radio.

Enter 6.0, 9.0, 12.0, 18.0, 24.0, 36.0, 48.0, and 54.0 to set these data rates to enabled on the 5-GHz radio.

(Optional) Enter basic-1.0, basic-2.0, basic-5.5, and basic-11.0 to set these data rates to basic on the 802.11b, 2.4-GHz radio.

Enter basic-1.0, basic-2.0, basic-5.5, basic-6.0, basic-9.0, basic-11.0, basic-12.0, basic-18.0, basic-24.0, basic-36.0, basic-48.0, and basic-54.0 to set these data rates to basic on the 802.11g, 2.4-GHz radio.

Note If the client must support the basic rate that you select, it cannot associate to the wireless device. If you select 12-Mb/s or higher for the basic data rate on the 802.11g radio, 802.11b client devices cannot associate to the wireless device 802.11g radio.

Enter basic-6.0, basic-9.0, basic-12.0, basic-18.0, basic-24.0, basic-36.0, basic-48.0, and basic-54.0 to set these data rates to basic on the 5-GHz radio.

(Optional) Enter range or throughput or ofdm-throughput (no ERP protection) to automatically optimize radio range or throughput. When you enter range, the wireless device sets the lowest data rate to basic and sets the other rates to enabled. When you enter throughput, the wireless device sets all data rates to basic.

(Optional) On the 802.11g radio, enter speed throughput ofdm to set all OFDM rates (6, 9, 12, 18, 24, 36, and 48) to basic (required) and to set all the CCK rates (1, 2, 5.5, and 11) to disabled. This setting disables 802.11b protection mechanisms and provides maximum throughput for 802.11g clients. However, it prevents 802.11b clients from associating to the access point.

(Optional) Enter default to set the data rates to factory default settings (not supported on 802.11b radios).

On the 802.11g radio, the default option sets rates 1, 2, 5.5, and 11 to basic, and sets rates 6, 9, 12, 18, 24, 36, 48, and 54 to enabled. These rate settings allow both 802.11b and 802.11g client devices to associate to the wireless device 802.11g radio.

On the 5-GHz radio, the default option sets rates 6.0, 12.0, and 24.0 to basic, and sets rates 9.0, 18.0, 36.0, 48.0, and 54.0 to enabled.

On the 802.11g/n 2.4-GHz radio, the default option sets rates 1.0, 2.0, 5.5, and 11.0 to enabled.

On the 802.11g/n 5-GHz radio, the default option sets rates to 6.0, 12.0, and 24.0 to enabled.

The modulation coding scheme (MCS) index range for both 802.11g/n radios is 0 to 15.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the speed command to remove one or more data rates from the configuration. This example shows how to remove data rates basic-2.0 and basic-5.5 from the configuration:

ap1200# configure terminal
ap1200(config)# interface dot11radio 0
ap1200(config-if)# no speed basic-2.0 basic-5.5
ap1200(config-if)# end
 
 

Configuring MCS Rates

Modulation coding scheme (MCS) is a specification of PHY parameters consisting of modulation order (binary phase shift keying [BPSK], quaternary phase shift keying [QPSK], 16-quadrature amplitude modulation [16-QAM], 64-QAM) and forward error correction (FEC) code rate (1/2, 2/3, 3/4, 5/6). MCS is used in the wireless device 802.11n radios, which define 32 symmetrical settings (8 per spatial stream):

MCS 0-7

MCS 8-15

MCS 16-23

MCS 24-31

The wireless device supports MCS 0-15. High-throughput clients support at least MCS 0-7.

MCS is an important setting because it provides for potentially greater throughput. High-throughput data rates are a function of MCS, bandwidth, and guard interval. The 802.11a, b, and g radios use 20-MHz channel widths. Table 1 shows potential data rated based on MCS, guard interval, and channel width.

Table 1 Data Rates Based on MCS Settings, Guard Interval, and Channel Width  

MCS Index
Guard Interval = 800 ns
Guard Interval = 400 ns
 
20-MHz Channel Width Data Rate (Mb/s)
40-MHz Channel Width Data Rate (Mb/s)
20-MHz Channel Width Data Rate (Mb/s)
40-MHz Channel Width Data Rate (Mb/s)

0

6.5

13.5

7 2/9

15

1

13

27

14 4/9

30

2

19.5

40.5

21 2/3

45

3

26

54

28 8/9

60

4

39

81

43 1/3

90

5

52

109

57 5/9

120

6

58.5

121.5

65

135

7

65

135

72 2/9

152.5

8

13

27

14 4/9

30

9

26

54

28 8/9

60

10

39

81

43 1/3

90

11

52

108

57 7/9

120

12

78

162

86 2/3

180

13

104

216

115 5/9

240

14

117

243

130

270

15

130

270

144 4/9

300

The legacy rates are as follows:

5 GHz: 6, 9, 12, 18, 24, 36, 48, and 54 Mb/s

2.4 GHz: 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48, and 54 Mb/s


MCS rates are configured using the speed command. The following example shows a speed setting for an 802.11g/n 2.4-GHz radio:

interface Dot11Radio0
no ip address
no ip route-cache
!
ssid 800test
!
speed basic-1.0 2.0 5.5 11.0 6.0 9.0 12.0 18.0 24.0 36.0 48.0 54.0 m0. m1. m2. m3. m4. m8. 
m9. m10. m11. m12. m13. m14. m15.
 
 

Configuring Radio Transmit Power

Radio transmit power is based on the type of radio or radios installed in your access point and the regulatory domain in which it operates.

To set the transmit power on access point radios, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. power local level

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface.

The 2.4-GHz and the 802.11g/n 2.4-GHz radios are radio 0.

The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 3 

power local

These options are available for the 2.4-GHz 802.11n radio (in dBm):

{8 | 9| 11 | 14 | 15 | 17 | maximum}

Sets the transmit power for the radio, or the 5-GHz radio so that the power level is allowed in your regulatory domain.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the power local command to return the power setting to maximum, the default setting.

Limiting the Power Level for Associated Client Devices

You can also limit the power level on client devices that associate to the wireless device. When a client device associates to the wireless device, the wireless device sends the maximum power level setting to the client.


Note Cisco AVVID documentation uses the term Dynamic Power Control (DPC) to refer to limiting the power level on associated client devices.


To specify a maximum allowed power setting on all client devices that associate to the wireless device, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. power client level

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 2.4-GHz and 802.11g/n 2.4-GHz radios are radio 0.

The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 3 

power client

These options are available for 802.11n 2.4-GHz clients (in dBm):

{local | 8 | 9 | 11 | 14 | 15 | 17 | maximum}

These options are available for 802.11n 5-GHz clients (in dBm):

{local | 8 | 11 | 13 | 14 | 15 | maximum}

Sets the maximum power level allowed on client devices that associate to the wireless device.

Setting the power level to local sets the client power level to that of the access point.

Setting the power level to maximum sets the client power to the allowed maximum.

Note The settings allowed in your regulatory domain might differ from the settings listed here.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the power client command to disable the maximum power level for associated clients.


Note Aironet extensions must be enabled to limit the power level on associated client devices. Aironet extensions are enabled by default.


Configuring Radio Channel Settings

The default channel setting for the wireless device radios is least congested. At startup, the wireless device scans for and selects the least-congested channel. For the most consistent performance after a site survey, however, we recommend that you assign a static channel setting for each access point. The channel settings on the wireless device correspond to the frequencies available in your regulatory domain. See the hardware installation guide for the access point for the frequencies allowed in your domain.

Each 2.4-GHz channel covers 22 MHz. Because the bands for channels 1, 6, and 11 do not overlap, you can set up multiple access points in the same vicinity without causing interference. The 802.11b and 802.11g 2.4-GHz radios use the same channels and frequencies.

The 5-GHz radio operates on 8 channels from 5180 to 5320 MHz, up to 27 channels from 5170 to 5850 MHz depending on regulatory domain. Each channel covers 20 MHz, and the bands for the channels overlap slightly. For best performance, use channels that are not adjacent (use channels 44 and 46, for example) for radios that are close to each other.


Caution The presence of too many access points in the same vicinity can create radio congestion that can reduce throughput. A careful site survey can determine the best placement of access points for maximum radio coverage and throughput.

802.11n Channel Widths

The 802.11n standard allows both 20-MHz and 40-Mhz channel widths consisting of two contiguous non-overlapping channels (for example, 2.4-GHz channels 1 and 6).

One of the 20-MHz channels is called the control channel. Legacy clients and 20-MHz high-throughput clients use the control channel. Only beacons can be sent on this channel. The second 20-MHz channel is called the extension channel. The 40-MHz stations may use this channel and the control channel simultaneously.

A 40-MHz channel is specified as a channel and extension, such as 1,1. In this example, the control channel is channel 1 and the extension channel is above it.

To set the wireless device channel width, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0 | 1}

3. channel {frequency | least-congested | width [20 | 40-above | 40-below] | dfs}

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0 | 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

channel
{frequency | least-congested | width [20 | 40-above | 40-below] | dfs}

Sets the default channel for the wireless device radio.To search for the least-congested channel on startup, enter least-congested.

Use the width option to specify a bandwidth to use. This option is available for the Cisco 800 series ISR wireless devices and consists of three available settings: 20, 40-above, and 40-below:

Choosing 20 sets the channel width to 20 MHz.

Choosing 40-above sets the channel width to 40 MHz with the extension channel above the control channel.

Choosing 40-below sets the channel width to 40 MHz with the extension channel below the control channel.

Note The channel command is disabled for 5-GHz radios that comply with European Union regulations on dynamic frequency selection (DFS). See the "Enabling and Disabling World Mode" section for more information.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Dynamic Frequency Selection

Access points with 5-GHz radios configured at the factory for use in the United States, Europe, Singapore, Korea, Japan, Israel, and Taiwan now comply with regulations that require radio devices to use Dynamic Frequency Selection (DFS) to detect radar signals and avoid interfering with them. When an access points detects a radar on a certain channel, it avoids using that channel for 30 minutes. Radios configured for use in other regulatory domains do not use DFS.

When a DFS-enabled 5-GHz radio operates on one of the 15 channels listed in Table 2, the access point automatically uses DFS to set the operating frequency. When DFS is enabled, the access point monitors its operating frequency for radar signals. If it detects radar signals on the channel, the access point takes these steps:

Blocks new transmissions on the channel.

Flushes the power-save client queues.

Broadcasts an 802.11h channel-switch announcement.

Disassociates remaining client devices.

If participating in WDS, sends a DFS notification to the active WDS device that it is leaving the frequency.

Randomly selects a different 5-GHz channel.

If the channel selected is one of the channels in Table 2, scans the new channel for radar signals for 60 seconds.

If there are no radar signals on the new channel, enables beacons and accepts client associations.

If participating in WDS, sends a DFS notification of its new operating frequency to the active WDS device.


Note You cannot manually select a channel for DFS-enabled 5-GHz radios in Europe and Singapore. The access points randomly selects a channel. However, in Japan, you can manually select a channel if a radar has not been detected on it for the previous 30 minutes. If you attempt to select a channel that is unavailable due to radar detection, the CLI displays a message stating the channel is unavailable.


The full list of channels that require DFS is shown in Table 2.

Table 2 DFS Channel List 

Channel
Frequency
Channel
Frequency
Channel
Frequency

56

5280 MHz

108

5520 MHz

128

5640 MHz

60

5300 MHz

112

5560 MHz

132

5660 MHz

64

5320 MHz

116

5580 MHz

136

5680 MHz

100

5500 MHz

120

5600 MHz

140

5700 MHz

104

5500 MHz

124

5620 MHz


For autonomous operation, DFS requires random channel selection among the channels listed in Table 2. The user interface prevents you from manually configuring these channels. The channels that are not listed in Table 2 do not require random selection and may be manually configured.

Prior to transmitting on any channels listed in Table 2, the access point radio performs a Channel Availability Check (CAC). The CAC is a 60 second scan for the presence of radar signals on the channel. The following sample messages are displayed on the access point console showing the beginning and end of the CAC scan:

*Mar 6 07:37:30.423: %DOT11-6-DFS_SCAN_START: DFS: Scanning frequency 5500 MHz for 60 seconds

*Mar 6 07:37:30.385: %DOT11-6-DFS_SCAN_COMPLETE: DFS scan complete on frequency 5500 MHz

When operating on any of the DFS channels listed in Table 2, in addition to performing the CAC, the access point constantly monitors the channel for radar. If radar is detected, the access point stops forwarding data packets within 200 ms and broadcasts five beacons that include an 802.11h channel switch announcement, indicating the channel number that the access point begins using. The following example message displays on the access point console when radar is detected:

*Mar 6 12:35:09.750: %DOT11-6-DFS_TRIGGERED: DFS: triggered on frequency 5500 MHz

When radar is detected on a channel, that channel may not be used for 30 minutes. The access point maintains a flag in non-volatile storage for each channel that it detects radar on in the last 30 minutes. After 30 minutes, the flag is cleared for the corresponding channel. If the access point is rebooted before a flag is cleared, the non-occupancy time is reset to 30 minutes when the channel initializes.


Note The maximum legal transmit power is greater for some 5-GHz channels than for others. When it randomly selects a 5-GHz channel on which power is restricted, the access point automatically reduces transmit power to comply with power limits for that channel.



Note Cisco recommends that you use the world-mode dot11d country-code configuration interface command to configure a country code on DFS-enabled radios. The IEEE 802.11h protocol requires access points to include the country information element (IE) in beacons and probe responses. By default, however, the country code in the IE is blank. You use the world-mode command to populate the country code IE.


CLI Commands

The following sections describe CLI commands that apply to DFS.

Confirming that DFS is Enabled

Use the show controllers dot11radio1 command to confirm that DFS is enabled. The command also includes indications that uniform spreading is required and channels that are in the non-occupancy period due to radar detection.

This example shows a line from the output for the show controller command for a channel on which DFS is enabled. The indications listed in the previous paragraph are shown in bold:

ap# show controller dot11radio1
!
interface Dot11Radio1
Radio <model>, Base Address 011.9290ec0, BBlock version 0.00, Software version 6.00.0
Serial number FOCO83114WK
Number of supported simultaneous BSSID on Dot11Radio1: 8
Carrier Set: Americas (OFDM) (US )
Uniform Spreading Required: Yes
Current Frequency: 5300 MHz Channel 60 (DFS enabled)
Current Frequency: 5300 MHz  Channel 60 (DFS enabled)
Allowed Frequencies: 5180(36) 5200(40) 5220(44) 5240(48) *5260(52) *5280(56) *53
00(60) *5320(64) *5500(100) *5520(104) *5540(108) *5560(112) *5580(116) *5660(13
2) *5680(136) *5700(140) 5745(149) 5765(153) 5785(157) 5805(161)
* = May only be selected by Dynamic Frequency Selection (DFS)
 
 
Listen Frequencies: 5170(34) 5190(38) 5210(42) 5230(46) 5180(36) 5200(40) 5220(4
4) 5240(48) 5260(52) 5280(56) 5300(60) 5320(64) 5500(100) 5520(104) 5540(108) 55
60(112) 5580(116) 5600(120) 5620(124) 5640(128) 5660(132) 5680(136) 5700(140) 57
45(149) 5765(153) 5785(157) 5805(161) 5825(165)
 
 
DFS Blocked Frequencies: none
Beacon Flags: 0; Beacons are enabled; Probes are enabled
Current Power: 17 dBm
Allowed Power Levels: -1 2 5 8 11 14 15 17
Allowed Client Power Levels: 2 5 8 11 14 15 17
...

Configuring a Channel

Use the channel command to configure a channel. The command for the interface is modified to only allow you to select a specific channel number and to enable DFS.

To configure a channel, follow these steps.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio1 dfs simulate

3. channel {number | dfs band <1-4>}

4. end

5. show running-config

6. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio1 dfs simulate

Enters the configuration interface for the 802.11a radio

Step 3 

channel {number | dfs band <1-4>}

Specifies the channel to use.

For number, enter one of the following channels: 36, 40, 44, 48, 149, 153, 157, 161, 5180, 5200, 5220, 5240, 5745, 5765, 5785, or 5805.

Enter dfs and one of the following frequency bands to use dynamic frequency selection on the selected channel:

1—5.150 to 5.250 GHz

2—5.250 to 5.350 Ghz

3—5.470 to 5.725 GHz

4—5.725 to 5.825 GHz

If you attempt to configure a channel that may only be selected by dfs, the following message appears:

This channel number/frequency can only be used by 
Dynamic Frequency Selection (DFS)

Step 4 

end

Returns to the privileged EXEC mode.

Step 5 

show running-config

Verifies your entries

Step 6 

copy running-config startup-config

(Optional) Saves your entries to the configuration file.

The following example selects channel 36 and configures it to use DFS on a frequency band 1:

ap# configure terminal 
ap(config)interface dot11radio1 
ap(config-if) channel 36 
ap(config-if)

Blocking Channels from DFS Selection

If your regulatory domain limits the channels that you can use in specific locations—for example, indoors or outdoors—you can block groups of channels to prevent the access point from selecting them when DFS is enabled. Use this configuration interface command to block groups of channels from DFS selection:

[no] dfs band [1] [2] [3] [4] block

The 1, 2, 3, and 4 options designate blocks of channels:

1—Specifies frequencies 5.150 to 5.250 GHz. This group of frequencies is also known as the UNII-1 band.

2—Specifies frequencies 5.250 to 5.350 GHz. This group of frequencies is also known as the UNII-2 band.

3—Specifies frequencies 5.470 to 5.725 GHz.

4—Specifies frequencies 5.725 to 5.825 GHz. This group of frequencies is also known as the UNII-3 band.

This example shows how to prevent the access point from selecting frequencies 5.150 to 5.350 GHz during DFS:

ap(config-if)# dfs band 1 2 block
 
 

This example shows how to unblock frequencies 5.150 to 5.350 for DFS:

ap(config-if)# no dfs band 1 2 block
 
 

This example shows how to unblock all frequencies for DFS:

ap(config-if)# no dfs band block
 
 

Simulating Radar Detection

You can simulate radar detection on the current channel using the debug dot11 dfs simulate command. The following example simulates radar on dfs channel 36. Five beacons are sent.

ap>enable
Password:
ap#debug dot11 dot11radio1 dfs simulate 36 5
 
 

The following is an example message displayed on the console when radar is detected:

*Mar 6 12:35:09.750: %DOG11-6-DFS_TRIGGERED: DFS: triggered on frequency 5500 MHz

Setting the 802.11n Guard Interval

The 802.11n guard interval is the period in nanoseconds between packets. Two settings are available: short (400ns) and long (800ns).

To to set the 802.11n guard interval, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0 | 1}

3. guard-interval {any | long}

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0 | 1}

Enters interface configuration mode for the radio interface.The 802.11n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

guard-interval {any | long}

Specifies a guard interval.

any allows either the short (400ns) or long (800ns) guard interval.

long allows only the long (800ns) guard interval.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Enabling and Disabling World Mode

You can configure the wireless device to support 802.11d world mode, Cisco legacy world mode, or world mode roaming. When you enable world mode, the wireless device adds channel carrier set information to its beacon. Client devices with world mode enabled receive the carrier set information and adjust their settings automatically. For example, a client device used primarily in Japan could rely on world mode to adjust its channel and power settings automatically when it travels to Italy and joins a network there. Cisco client devices detect whether the wireless device is using 802.11d or Cisco legacy world mode and automatically use the world mode that matches the mode used by the wireless device.

You can also configure world mode to be always on. In this configuration, the access point essentially roams between countries and changes its settings as required.

World mode is disabled by default.

To enable world mode, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. world-mode {dot11d country_code code {both | indoor | outdoor} | world-mode roaming | legacy}

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface.

Step 3 

world-mode
{dot11d country_code code
{both | indoor | outdoor}
|
world-mode roaming | legacy}

Enables world mode.

Enter the dot11d option to enable 802.11d world mode.

When you enter the dot11d option, you must enter a 2-character ISO country code (for example, the ISO country code for the United States is US). You can find a list of ISO country codes at the ISO website.

After the country code, you must enter indoor, outdoor, or both to indicate the placement of the wireless device.

Enter the legacy option to enable Cisco legacy world mode.

Enter the world-mode roaming option to place the access point in a continuous world mode configuration.

Note Aironet extensions must be enabled for legacy world mode operation, but Aironet extensions are not required for 802.11d world mode. Aironet extensions are enabled by default.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the world-mode command to disable world mode.

Disabling and Enabling Short Radio Preambles

The radio preamble (sometimes called a header) is a section of data at the head of a packet that contains information that the wireless device and client devices need when sending and receiving packets. You can set the radio preamble to long or short:

Short—A short preamble improves throughput performance.

Long—A long preamble ensures compatibility between the wireless device and all early models of Cisco Aironet Wireless LAN Adapters. If these client devices do not associate to the wireless devices, you should use short preambles.

You cannot configure short or long radio preambles on the 5-GHz radio.

To disable short radio preambles, follow these steps, beginning in privileged EXEC mode:

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. no preamble-short

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the 2.4-GHz radio interface.

Step 3 

no preamble-short

Disables short preambles and enable long preambles.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Short preambles are enabled by default. Use the preamble-short command to enable short preambles if they are disabled.

Configuring Transmit and Receive Antennas

You can select the antenna that the wireless device uses to receive and transmit data. There are three option settings for both the receive antenna (see step 4) and the transmit antenna (see step 5):

Gain—Sets the resultant antenna gain in decibels (dB).

Diversity—This default setting tells the wireless device to use the antenna that receives the best signal. If the wireless device has two fixed (non-removable) antennas, you should use this setting for both receive and transmit.

Right—If the wireless device has removable antennas and you install a high-gain antenna on the wireless device's right connector, you should use this setting for both receive and transmit. When you look at the wireless device's back panel, the right antenna is on the right.

Left—If the wireless device has removable antennas and you install a high-gain antenna on the wireless device's left connector, you should use this setting for both receive and transmit. When you look at the wireless device's back panel, the left antenna is on the left.

To select the antennas that the wireless device uses to receive and transmit data, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. gain dB

4. antenna receive {diversity | left | right}

5. antenna transmit {diversity | left | right}

6. end

7. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

gain dB

Specifies the resultant gain of the antenna attached to the device. Enter a value from -128 to 128 dB. If necessary, you can use a decimal point in the value, such as "1.5".

Step 4 

antenna receive
{diversity | left | right}

Sets the receive antenna to diversity, left, or right.

Note For best performance with two antennas, leave the receive antenna setting at the default setting, diversity. For one antenna, attach the antenna on the right and set the antenna for right.

Step 5 

antenna transmit
{diversity | left | right}

Sets the transmit antenna to diversity, left, or right.

Note For best performance with two antennas, leave the receive antenna setting at the default setting, diversity. For one antenna, attach the antenna on the right and set the antenna for right.

Step 6 

end

Returns to privileged EXEC mode.

Step 7 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Enabling and Disabling Gratuitous Probe Response

Gratuitous Probe Response (GPR) aids in conserving battery power in dual mode phones that support cellular and WLAN modes of operation. GPR is available on 5-Ghz radios and is disabled by default. You can configure two GPR settings:

Period—This setting determines the time between GPR transmissions in Kusec intervals from 10 to 255 (similar to the beacon period)

Speed—The speed is the data rate used to transmit the GPR

Selecting a longer period reduces the amount of RF bandwidth consumed by the GPR with the possibility of shorter battery life. Selecting higher transmission speeds also reduces the amount of bandwidth consumed but at the expense of a smaller cell size.

To enable GPR and set its parameters, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {

3. probe-response gratuitous {period | speed}

4. period Kusec

5. speed {[6.0] [9.0] [12.0] [18.0] [24.0] [36.0] [48.0] [54.0]}

6. end

7. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {

Enters interface configuration mode for the 5-GHz radio interface.

Step 3 

probe-response gratuitous
{period | speed}

Enables the Gratuitous Probe Response feature using default period (10 Kusec) and speed (6.0 Mbps).

Step 4 

period Kusec

(Optional) Accepts a value from 10 to 255. The default value is 10

Step 5 

speed
{[6.0] [9.0] [12.0] [18.0] [24.0] [36.0] [48.0] [54.0]}

(Optional) Sets the response speed in Mbps. The default value is 6.0.

Step 6 

end

Returns to privileged EXEC mode.

Step 7 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

The optional parameters can be configured independently or combined when you do not want to use the defaults, as shown in the following examples:

(config-if)# probe-response gratuitous period 30
(config-if)# probe-response gratuitous speed 12.0
(config-if)# probe-response gratuitous period 30 speed 12.0
 
 

Use the no form of the command to disable the GPR feature.

Disabling and Enabling Aironet Extensions

By default, the wireless device uses Cisco Aironet 802.11 extensions to detect the capabilities of Cisco Aironet client devices and to support features that require specific interaction between the wireless device and associated client devices. Aironet extensions must be enabled to support these features:

Load balancing—Wireless device uses Aironet extensions to direct client devices to an access point that provides the best connection to the network on the basis of such factors as number of users, bit error rates, and signal strength.

Message Integrity Check (MIC)—MIC is an additional WEP security feature that prevents attacks on encrypted packets called bit-flip attacks. The MIC, implemented on the wireless device and all associated client devices, adds a few bytes to each packet to make the packets tamper-proof.

Cisco Key Integrity Protocol (CKIP)—Cisco's WEP key permutation technique is based on an early algorithm presented by the IEEE 802.11i security task group. The standards-based algorithm, Temporal Key Integrity Protocol (TKIP), does not require Aironet extensions to be enabled.

World mode (legacy only)—Client devices with legacy world mode enabled receive carrier set information from the wireless device and adjust their settings automatically. Aironet extensions are not required for 802.11d world mode operation.

Limiting the power level on associated client devices—When a client device associates to the wireless device, the wireless device sends the maximum allowed power level setting to the client.

Disabling Aironet extensions disables the features listed above, but it sometimes improves the ability of non-Cisco client devices to associate to the wireless device. Aironet extensions are enabled by default. To disable Aironet extensions, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. no dot11 extension aironet

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface.

The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

no dot11 extension aironet

Disables Aironet extensions.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the dot11 extension aironet command to enable Aironet extensions if they are disabled.

Configuring the Ethernet Encapsulation Transformation Method

When the wireless device receives data packets that are not 802.3 packets, the wireless device must format the packets to 802.3 by using an encapsulation transformation method. These are the two transformation methods:

802.1H—This method provides optimum performance for Cisco wireless products.

RFC 1042—Use this setting to ensure interoperability with non-Cisco wireless equipment. RFC1042 does not provide the interoperability advantages of 802.1H but is used by other manufacturers of wireless equipment.

To configure the encapsulation transformation method, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. payload-encapsulation {snap | dot1h}

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

payload-encapsulation
{snap | dot1h}

Sets the encapsulation transformation method to RFC 1042 (snap) or 802.1h (dot1h, the default setting).

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Enabling and Disabling Public Secure Packet Forwarding

Public Secure Packet Forwarding (PSPF) prevents client devices that are associated to an access point from inadvertently sharing files or communicating with other client devices that are associated to the access point. PSPF provides Internet access to client devices without providing other capabilities of a LAN. This feature is useful for public wireless networks like those installed in airports or on college campuses.


Note To prevent communication between clients associated to different access points, you must set up protected ports on the switch to which the wireless devices are connected. See the "Configuring Protected Ports" section for instructions on setting up protected ports.


To enable and disable PSPF using command-line interface (CLI) commands on the wireless device, you use bridge groups. You can find a detailed explanation of bridge groups and instructions for implementing them in this document:

Cisco IOS Bridging and IBM Networking Configuration Guide, Release 12.2. Click this link to browse to the Configuring Transparent Bridging chapter: http://www.cisco.com/en/US/docs/ios/12_2/ibm/configuration/guide/
bcftb_ps1835_TSD_Products_Configuration_Guide_Chapter.html

PSPF is disabled by default. To enable PSPF, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. bridge-group group port-protected

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

bridge-group group port-protected

Enables PSPF.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the bridge group command to disable PSPF.

Configuring Protected Ports

To prevent communication between client devices that are associated to different access points on your wireless LAN, you must set up protected ports on the switch to which the wireless devices are connected.

To define a port on your switch as a protected port, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface interface-id

3. switchport protected

4. end

5. show interfaces interface-id switchport

6. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface interface-id

Enters interface configuration mode. Enter the type and number of the switch port interface to configure, such as wlan-gigabitethernet0.

Step 3 

switchport protected

Configures the interface to be a protected port.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

show interfaces interface-id switchport

Verifies your entries.

Step 6 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

To disable protected port, use the no switchport protected command.

For detailed information on protected ports and port blocking, see the "Configuring Port-Based Traffic Control" chapter in Catalyst 3550 Multilayer Switch Software Configuration Guide, 12.1(12c)EA1. Click this link to browse to that guide:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_12c_ea1/
configuration/guide/3550scg.html

Configuring the Beacon Period and the DTIM

The beacon period is the amount of time between access point beacons in kilomicroseconds (Kmicrosecs). One Kmicrosec equals 1,024 microseconds. The data beacon rate, always a multiple of the beacon period, determines how often the beacon contains a delivery traffic indication message (DTIM). The DTIM tells power-save client devices that a packet is waiting for them.

For example, if the beacon period is set at 100, its default setting, and if the data beacon rate is set at 2, its default setting, then the wireless device sends a beacon containing a DTIM every 200 Kmicrosecs.

The default beacon period is 100, and the default DTIM is 2. To configure the beacon period and the DTIM, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. beacon period value

4. beacon dtim-period value

5. end

6. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

beacon period value

Sets the beacon period. Enter a value in kilomicroseconds.

Step 4 

beacon dtim-period value

Sets the DTIM. Enter a value in kilomicroseconds.

Step 5 

end

Returns to privileged EXEC mode.

Step 6 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configure RTS Threshold and Retries

The request to send (RTS) threshold determines the packet size at which the wireless device issues an RTS before sending the packet. A low RTS threshold setting can be useful in areas where many client devices are associating with the wireless device, or in areas where the clients are far apart and can detect only the wireless device and not detect each other. You can enter a setting ranging from 0 to 2347 bytes.

Maximum RTS retries is the maximum number of times the wireless device issues an RTS before stopping the attempt to send the packet over the radio. Enter a value from 1 to 128.

The default RTS threshold is 2347 for all access points and bridges, and the default maximum RTS retries setting is 32.

To configure the RTS threshold and maximum RTS retries, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. rts threshold value

4. rts retries value

5. end

6. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 2.4-GHz and the 802.11g/n 2.4-GHz radios are radio 0. The 5-GHz and the 802.11n 5-GHz radio is radio 1.

Step 3 

rts threshold value

Sets the RTS threshold. Enter an RTS threshold from 0 to 2347.

Step 4 

rts retries value

Sets the maximum RTS retries. Enter a setting from 1 to 128.

Step 5 

end

Returns to privileged EXEC mode.

Step 6 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the rts command to reset the RTS settings to defaults.

Configuring the Maximum Data Retries

The maximum data retries setting determines the number of attempts that the wireless device makes to send a packet before it drops the packet. The default setting is 32.

To configure the maximum data retries, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. packet retries value

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz radio is radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

packet retries value

Sets the maximum data retries. Enter a setting from 1 to 128.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the packet retries command to reset the setting to the default.

Configuring the Fragmentation Threshold

The fragmentation threshold determines the size at which packets are fragmented (sent as several pieces instead of as one block). Use a low setting in areas where communication is poor or where there is a great deal of radio interference. The default setting is 2346 bytes.

To configure the fragmentation threshold, follow these steps, beginning in privileged EXEC mode.

SUMMARY STEPS

1. configure terminal

2. interface dot11radio {0| 1}

3. fragment-threshold value

4. end

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

configure terminal

Enters global configuration mode.

Step 2 

interface dot11radio {0| 1}

Enters interface configuration mode for the radio interface. The 802.11g/n 2.4-GHz and 5-GHz radios are radio 0.

The 802.11n 5-GHz radio is radio 1.

Step 3 

fragment-threshold value

Sets the fragmentation threshold. Enter a setting from 256 to 2346 bytes for the 2.4-GHz radio. Enter a setting from 256 to 2346 bytes for the 5-GHz radio.

Step 4 

end

Returns to privileged EXEC mode.

Step 5 

copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Use the no form of the fragment-threshold command to reset the setting to the default.

Enabling Short Slot Time for 802.11g Radios

You can increase throughput on the 802.11g 2.4-GHz radio by enabling short slot time. Reducing the slot time from the standard 20 microseconds to the 9-microsecond short slot time decreases the overall backoff, which increases throughput. Backoff, which is a multiple of the slot time, is the random length of time that a station waits before sending a packet on the LAN.

Many 802.11g radios support short slot time, but some do not. When you enable short slot time, the wireless device uses the short slot time only when all clients associated to the 802.11g 2.4-GHz radio support short slot time.

Short slot time is supported only on the 802.11g 2.4-GHz radio. Short slot time is disabled by default.

In radio interface mode, enter the short-slot-time command to enable short slot time:

ap(config-if)# short-slot-time 

Enter no short-slot-time command to disable short slot time.

Performing a Carrier Busy Test

You can perform a carrier busy test to check the radio activity on wireless channels. During the carrier busy test, the wireless device drops all associations with wireless networking devices for 4 seconds while it conducts the carrier test and then displays the test results.

In privileged EXEC mode, enter this command to perform a carrier busy test:

dot11 interface-number carrier busy 

For interface-number, enter dot11radio 0 to run the test on the 2.4-GHz radio, or enter dot11radio 1 to run the test on the 5-GHz radio.

Use the show dot11 carrier busy command to redisplay the carrier busy test results.

Configuring VoIP Packet Handling

You can improve the quality of VoIP packet handling per radio on access points by enhancing 802.11 MAC behavior for lower latency for the class of service (CoS) 5 (Video) and CoS 6 (Voice) user priorities.

To configure VoIP packet handling on an access point, follow these steps:


Step 1 Using a browser, log in to the access point.

Step 2 Click Services in the task menu on the left side of the web-browser interface.

Step 3 When the list of Services expands, click Stream.

The Stream page appears.

Step 4 Click the tab for the radio to configure.

Step 5 For both CoS 5 (Video) and CoS 6 (Voice) user priorities, choose Low Latency from the Packet Handling drop-down menu, and enter a value for maximum retries for packet discard in the corresponding field.

The default value for maximum retries is 3 for the Low Latency setting (Figure 2). This value indicates how many times the access point will try to retrieve a lost packet before discarding it.

Figure 2 Packet Handling Configuration


Note You may also configure the CoS 4 (Controlled Load) user priority and its maximum retries value.


Step 6 Click Apply.


You can also configure VoIP packet handling using the CLI. For a list of Cisco IOS commands for configuring VoIP packet handling using the CLI, consult Cisco IOS Command Reference for Cisco Aironet Access Points and Bridges.