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Can Cisco Aironet 1200 series APs support 802.11b and 802.11g clients simultaneously?

Core Issue

The 802.11b and 802.11g radios use the same frequencies.


Resolution

The Cisco 1200 series Access Point (AP) can support both the 802.11b clients and 802.11g clients simultaneously. 802.11g provides performance that is comparable to that of the 802.11a WLAN standard that operates in the 5-GHz band, while it also provides backward compatibility with the legacy 11-Mbps 802.11b standard. Like 802.11b, 802.11g operates in the same 2.4-GHz portion of the radio frequency spectrum that allows for license-free operation on a nearly worldwide basis. 802.11g is also limited to the same three non-overlapping channels as 802.11b.

To allow both the 802.11b and 802.11g clients, the data rates on the AP must be configured correctly. On the 802.11g radio, the default option sets rates 1, 2, 5.5, and 11 to basic, and 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. There are no other special configurations required to allow 802.11b and 802.11g clients to associate with the APs.

For more information on Configuring Radio Data Rates:-

You use the data rate settings to choose the data rates the wireless device uses for data transmission. The rates are expressed in megabits per second. The wireless device always attempts to transmit at the highest data rate set to Basic, also called Require 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 megabits per second (Mbps) service only, set the 11-Mbps 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 Mbps, 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 Mbps service only, set the 54-Mbps 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 Mbps rate to basic and the other rates to enabled. When you enter throughput for the data rate setting, the wireless device sets all four data rates to basic.

Beginning in privileged EXEC mode, follow these steps to configure the radio data rates:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

interface dot11radio { }

Enter interface configuration mode for the radio interface.

Step 3

speed

These options are available for the 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}

These options are available for the 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 }

These options are available for the 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 |default }

Set each data rate to basic or enabled, or enter range to optimize range orthroughput 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 toenabled 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-54.0to set these data rates to basic on the 802.11g, 2.4-GHz radio.

Note The client must support the basic rate that you select or it cannot associate to the wireless device. If you select 12 Mbps 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 to automatically optimize radio range or throughput. When you enter range, the wireless device sets the lowest data rate to basic and 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 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 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 rates 9.0, 18.0, 36.0, 48.0, and 54.0 to enabled.

Step 4

end

Return to privileged EXEC mode.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.


Use the no form of the speed command to disable data rates. When you use the no form of the command, all data rates are disabled except the rates you name in the command. This example shows how to disable data rate 1.0:

ap1200# configure terminal

ap1200(config)# interface dot11radio 0

ap1200(config-if)# no speed basic-2.0 basic-5.5 basic-11.0

ap1200(config-if)# end

Data rate 1 is disabled, and the rest of the rates are set to basic.

This example shows how to set up the wireless device for 11-Mbps service only:

ap1200# configure terminal

ap1200(config)# interface dot11radio 0

ap1200(config-if)# no speed basic-11.0

ap1200(config-if)# end

Data rate 11 is set to basic, and the rest of the data rates are set to disabled.

Configuring Radio Settings.

Note: The client must support the basic rate that is selected on the AP radio or it cannot associate to the wireless device. So, if 12 Mbps or higher is selected for the basic data rate on the 802.11g radio, 802.11b client devices cannot associate to the wireless device 802.11g radio.

In a mixed environment (where there are both 802.11b clients and 802.11g clients), there is a negative impact on the throughput. In a mixed environment the 802.11g radio switches or modulates from 802.11b data rates to 802.11g data rates depending on the client (whether is a 802.11b or 802.11g client), and is never able to have a consistent 54Mb on the 802.11g clients.

For more information on this subject, refer to Capacity Coverage & Deployment Considerations for IEEE 802.11g.

Problem Type

Product information

Products

AP 1200

WLAN adapters (wireless card) / ACU (Aironet Client Utility)

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