Cisco Systems OL-6415-04 manual Configuring QoS, Configuration Guidelines, Fixed Slot Time

Chapter 9 Configuring QoS

Configuring QoS

Configuring QoS

QoS is disabled by default (however, the radio interface always honors tagged 802.1P packets even when you have not configured a QoS policy). This section describes how to configure QoS on your access point. It contains this configuration information:

•Configuration Guidelines, page 9-5

•Adjusting Radio Access Categories, page 9-5

•Disabling IGMP Snooping Helper, page 9-6

Configuration Guidelines

Before configuring QoS on your access point, you should be aware of this information:

•The most important guideline in QoS deployment is to be familiar with the traffic on your wireless LAN. If you know the applications used by wireless client devices, the applications’ sensitivity to delay, and the amount of traffic associated with the applications, you can configure QoS to improve performance.

•QoS does not create additional bandwidth for your wireless LAN; it helps control the allocation of bandwidth. If you have plenty of bandwidth on your wireless LAN, you might not need to configure QoS.

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 Min and Max 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 that standard.

Cisco strongly recommends that you use the default settings on the Radio Access Categories page. 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 defaults, use the default settings listed in Table 9-1.

The values listed in Table 9-1are to the power of 2. The access point computes Contention Window values with this equation:

CW = 2 ** X minus 1

where X is the value from Table 9-1.

Table 9-1		Default QoS Radio Access Categories
	Class of Service		Min Contention Window	Max Contention Window	Fixed Slot Time	Transmit Opportunity
	Background		4	10	7	0
	Best Effort		4	10	3	0
	Video <100ms Latency		3	4	2	3008
	Voice <100ms Latency		2	3	2	1504
				Cisco Wireless ISR and HWIC Access Point Configuration Guide
	OL-6415-04						9-5