Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
5-19
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 5 Cisco Unified Wireless QoS
QoS Advanced Features for WLAN Infrastructure
IP Phones
shows the basic QoS Basis Service Set (QBSS) information element (IE) advertised by a
Cisco AP. The Load field indicates the portion of available bandwidth currently used to transport data
on that AP.
on that AP.
Figure 5-19
QBSS Information Element
There are actually three QBSS IEs that need to be supported in certain situations:
•
Old QBSS (Draft 6 (pre-standard))
•
New QBSS (Draft 13 802.11e (standard))
•
New distributed CAC load IE (a Cisco IE)
The QBSS used depends on the WMM and 7920 settings on the WLAN.
7920 phone support, shown in
, is a component of the WLC WLAN configuration that
enables the AP to include the appropriate QBSS element in its beacons. WLAN clients with QoS
requirements, such as the 7920 and 7921G, use these advertised QoS parameters to determine the best
AP with which to associate.
requirements, such as the 7920 and 7921G, use these advertised QoS parameters to determine the best
AP with which to associate.
The WLC provides 7920 support through the client call admission control (CAC) limit, or AP CAC limit.
These features provide the following:
These features provide the following:
•
Client CAC limit—The 7920 uses a call admission control setting that is set on the client. This
supports legacy 7920 code-pre 2.01.
supports legacy 7920 code-pre 2.01.
•
AP CAC limit—The 7920 uses CAC settings learned from WLAN advertisement.
The various combinations of WMM, client CAC limit, and AP CAC limit result in different QBSS IEs
being sent:
being sent:
•
If only WMM is enabled, IE number 2 (802.11e standard) QBSS Load IE is sent out in the beacons
and probe responses.
and probe responses.
•
If 7920 client CAC limit is to be supported, IE number 1 (the pre-standard QBSS IE) is sent out in
the beacons and probe responses on the bg radios.
the beacons and probe responses on the bg radios.
•
If 7920 AP CAC limit is to be supported, the number 3 QBSS IE is sent in the beacons and probe
responses for bg radios.
responses for bg radios.
Note
The various QBSS IEs use the same ID, and therefore the three QBSSs are mutually exclusive. For
example, the beacons and probe responses can contain only one QBSS IE.
example, the beacons and probe responses can contain only one QBSS IE.
Setting the Admission Control Parameters
shows a sample configuration screen for setting the voice parameters on the controller.
153873
1 Octet
1 Octet
4 bytes
Element ID
(11)
Length
Load