Beacon (beacon frame)

A beacon is a management frame that an access point sends for every SSID it broadcasts on a radio. The standard interval is 100 time units¹, about 102.4 ms, and the beacon goes out at the lowest basic rate the network allows. A vendor design guide states both points: each enabled SSID on a radio adds a beacon every 102.4 ms, sent at the minimum basic rate. Clients use beacons to find the network, and they also carry the schedule that power-save clients follow.

That makes beacons a standing cost. No client has to be sending anything for the channel to carry them. The cost scales with two settings you control: the number of SSIDs and the lowest basic rate. One capture-based test on a single 2.4 GHz channel put beacon airtime at 3% with one SSID at 1 Mbps and 33% with fifteen SSIDs at 1 Mbps. With the lowest rate at 54 Mbps, fifteen SSIDs took 2%. Treat these as one measurement, not a constant. The vendor guide notes that how many SSIDs a radio can afford depends on the beacon rate and on co-channel contention. See low data rates and management overhead for how this shows up on the floor, and airtime is finite for the budget it comes out of.

Each beacon also carries a traffic indication map. It tells sleeping clients that the AP is holding frames for them. A DTIM is a beacon that announces buffered broadcast and multicast frames will follow immediately, and DTIMs recur at the DTIM period. The AP buffers group traffic when any associated station is asleep. With a power-save client present, multicast waits for the next DTIM; with none, it is sent at once. A DTIM period of 3 at 102.4 ms therefore means buffered multicast can wait up to about 307 ms. That arithmetic is why implicit I/O traffic that rides multicast needs a look at the DTIM setting: see multicast and DTIM with implicit I/O.

A beacon does not guarantee delivery, and it does not bound latency. It is a schedule, and a schedule that burns airtime when it is crowded.

Ben Rutter. "Beacon (beacon frame)." OT Wireless, published October 18, 2026. https://otwireless.com/glossary/beacon/

Rutter, B. (2026, October 18). Beacon (beacon frame). OT Wireless. https://otwireless.com/glossary/beacon/

@misc{rutter2026beacon,
  author = {Rutter, Ben},
  title = {{Beacon (beacon frame)}},
  year = {2026},
  howpublished = {\url{https://otwireless.com/glossary/beacon/}},
  organization = {OT Wireless},
}