Tuesday, December 22, 2015

WiFi: What is beacon bursting? What are the tradeoffs?

Beacon bursting is a mechanism by which beacon frames for all the BSSs (Virtual APs) running on that radio are sent out one after the other instead of spreading them out equally in time over the beacon interval. The other approach to sending beacons is to spread them out equally over the beacon interval.

For example, consider the beacon interval is 100msec and you have 5 VAPs beaconing, then, with bursting all the beacons are sent back to back after the beacon interrupt. However, if you are not using bursting, beacons are spread across the 100msecs. Hence, every 20msec the radio will send out the beacon of a different VAP.

Comparison of timelines with and without beacon bursting

Tradeoff of using beacon bursting

  1. The advantage of beacon bursting for an access point is that it allows the AP to "roam" to other channels in between the beacon interval (the time duration between beacons). This beacon interval on most stock APs is about 100msec.
  2. All broadcast-multicast traffic for PS clients will go immediately after all the beacons go as opposed to being spread out and sent across the entire beacon interval.