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Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
OL-14209-01
Chapter 6 Configuring Radio Settings
Enabling Short Slot Time for 802.11g Radios
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 this command to enable short slot time:
ap(config-if)# slot-time-short
Enter
no slot-time-short
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 re-display 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 CoS 5 (Video) and CoS 6 (Voice) user priorities.
Follow these steps to configure VoIP packet handling on an access point:
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 6-3
). This value indicates
how many times the access point will try to retrieve a lost packet before discarding it.