This page enables you to define the parameters of Carrier Sense Multiple Access (CSMA) for each traffic access category. These parameters affect how packets are delivered for the different classes of service. See the QoS Policies page to determine the level of service you want.

These parameters should be modified with caution because radio behavior is affected. To revert to the default values, refer to the installation and configuration guide.

Min Contention Window

For each access category, enter the minimum contention window value. Channel access is prioritized by assigning smaller contention window values to a higher priority traffic class. If a channel is busy or a transmission collides, a node chooses a random number between 0 and the current contention window minimum.

Max Contention Window

For each access category, enter the maximum contention window value. The minimum contention window value is doubled each time a collision occurs until the maximum is reached. A small contention window value decreases the access delay but increases the probability of a collision.

Fixed Slot Time

For each access category, enter the fixed slot time. Channel access can be strictly prioritized by assigning smaller contention window values to a higher priority traffic class. Traffic in the access category must wait this fixed number of slots after each packet received before resuming its random back-off.

Transmit Opportunity

Enter the number of microseconds that qualified transmitters can transmit through the normal backoff procedure with a set of pending packets. Larger values allow a client to control the channel for longer periods of time, allowing it to achieve higher throughput in this access category at the expense of longer access times for all access categories.

Admission Control

The Admission Control check boxes control client use of the access categories. When you enable admission control for an access category, clients associated to the access point must complete the WMM admission control procedure before they can use that access category.

Optimized Voice

If you click this button, the following changes are made:

• The values of Access Category Definition are changed for optimized voice.
• The packet handling for user priority 5 and 6 are changed to low latency. (See Services>Stream>Packet Handlings per User Priority.)
• The Gratuitous Probe Response (GPR) is enabled on this radio. (See Network Interfaces > Radio1-802.11A > Setting.)

WPA Default

Click this button to return to the default values for the above fields.

Max Channel Capacity (%)

The default max channel capacity is 75%, and the range is from 0 to 100%. If the channel should have no calls, set this parameter to 0%. Otherwise, determine what percentage of voice calls can occupy the channel.

Roam Channel Capacity (%)

The default roam channel capacity is 6%, and the range is from 0 to 100%. Determine the percentage of calls that may roam into the cell or into the channel on another cell.

See Also: Services: QoS Policies, Services: QoS Policies - Advanced