User's Manual

11-2
Cisco 3200 Series Wireless MIC Software Configuration Guide
OL-7734-02
Chapter 11 Configuring QoS in a Wireless Environment
Understanding QoS for Wireless LANs
Understanding QoS for Wireless LANs
Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority
and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an
equal chance of being dropped.
When you configure QoS on the WMIC, you can select specific network traffic, prioritize it, and use
congestion-management and congestion-avoidance techniques to provide preferential treatment.
Implementing QoS in your wireless LAN makes network performance more predictable and bandwidth
utilization more effective.
When you configure QoS, you create QoS policies and apply the policies to the VLAN configured on
your WMIC. If you do not use VLANs on your network, you can apply your QoS policies to the WMIC’s
Ethernet and radio ports.
Note Configuring the limited WMIC QoS features typically are not enough to manage the traffic
when traffic can congest the limited 20 Mbps bandwidth
of the WMIC. We highly recommended
that you apply traffic shaping and other MQC based QoS features.
QoS for Wireless LANs Versus QoS on Wired LANs
The QoS implementation for wireless LANs differs from QoS implementations on other Cisco devices.
With QoS enabled, bridges perform the following:
• They do not classify packets; they prioritize packets based on DSCP value, client type (such as a
wireless phone), or the priority value in the 802.1q or 802.1p tag.
• They do not match packets using ACL; they use only MQC class-map for matching clauses.
• They do not construct internal DSCP values; they only support mapping by assigning IP DSCP,
Precedence, or Protocol values to Layer 2 COS values.
• They carry out EDCF like queuing on the radio egress port only.
• They do only FIFO queueing on the Ethernet egress port.
• They support only 802.1Q/P tagged packets. Bridges do not support ISL.
• They support only MQC policy-map set cos action.
To contrast the wireless LAN QoS implementation with the QoS implementation on other Cisco network
devices, see the Cisco IOS Quality of Service Solutions Configuration Guide at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/index.htm
Impact of QoS on a Wireless LAN
Wireless LAN QoS features are a subset of the proposed 802.11e draft. QoS on wireless LANs provides
prioritization of traffic from the WMIC over the WLAN based on traffic classification.
Just as in other media, you might not notice the effects of QoS on a lightly loaded wireless LAN. The
benefits of QoS become more obvious as the load on the wireless LAN increases, keeping the latency,
jitter, and loss for selected traffic types within an acceptable range.