Filter
Top Products
7-5
Cisco Wireless Router and HWIC Configuration Guide
OL-6415-03
Chapter 7 Configuring QoS on an Access Point
Configuration Guidelines
Cisco Wireless IP Phone 7920 Support
The Wireless IP Phone 7920 phone uses Cisco CDP message with Appliance VLAN-ID TLV to inform
the access point of its presence. The access point intercepts the CDP messages sent from the client, and
if it contains the Appliance VLAN-ID TLV, it should flag the client as VoIP phone client.
If VLAN is enabled, all phone clients should be associated to a single Voice VLAN. If VLAN is not
enabled, we advise that all the VoIP packets be classified by using the same user_priority value (6).
The access point always uses DIFS with minimum contention window (CW) value derived from the
CWmax and CWmin range parameters to prioritize voice traffic.
Radio Interface Transmit Queues
The radio maintains four priority queues, one for each traffic category, and 802.11e Enhanced DCF
(EDCF) to provide differentiate Distributed Coordination Function (DCF) access to the wireless
medium. An EDCF-aware access point is assigned distinct pairs of CWmin and CWmax parameters for
each traffic category. The CWmin and CWmax parameters can be modified through the CLI.
Adjusting Radio Access Categories
The access point uses the radio access categories to calculate backoff times for each packet. As a rule,
high-priority packets have short backoff times.
The default values in the minimum and maximum contention window fields, and in the slot time fields
are based on settings recommended in IEEE Draft Standard 802.11e. For detailed information on these
values, consult the standard.
We recommend that you use the default settings. Changing these values can lead to unexpected
blockages of traffic on your wireless LAN, and the blockages might be difficult to diagnose. If you
change these values and find that you need to reset them to the default values.
The values listed in Table 7-2 are to the power of 2. The access point computes contention window
values by using the equation CW = 2 ** X minus 1, where X is the value in Table 7-3.
Table 7-3 CWmin and CWmax Default Parameters
Priority Fixed slottime Number CWmin CWmax
0 6 15 1023
1 2 15 1023
21715
3137