Network Computing is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Adding 'Quality' to Wireless LANs: Page 6 of 7

A node can compete with other devices for access to the WLAN when its interframe space timer expires. Without prioritization, each device calculates a random back-off period before attempting to transmit. To ensure fairness, the back-off value also factors in prior unsuccessful contention attempts so a node that "lost" out to another node with a lower random back-off is more likely to "win" next time.

The original 802.11 MAC included a PCF (Point Coordination Function) that provided a shorter interframe spacing, and thus the capability to support airwave QoS. But it was inefficient and unpredictable, and therefore relegated to standards footnote status.

Meru Networks, an emerging WLAN infrastructure provider, offers a unique twist to QoS. Although Meru plans to support WMM and forthcoming 802.11e standards, it believes many enterprises require more sophisticated QoS.

Meru's Air Traffic Control technology coordinates communication across wireless cells. Each access point communicates with the centralized controller, maintaining a list of clients, their traffic flows and neighboring APs. The software dynamically load balances clients across APs and coordinates traffic transmission around all other Meru APs while limiting interference.

It also provides global resource management. All traffic flows get analyzed in terms of available resources and those in use. Air Traffic Control then specifies which flows receive priority: If a VoIP WLAN phone sends voice traffic upstream every 30 milliseconds, the software can set aside a time slot for that traffic so it's received reliably.