Beacon Packet Structure

This page describes the format of beacon frames.

Fixed Part

Every beacon frame starts out with these fields:

Optional Part

More optional data can be specified as part of the beacon. These optional fields are each specified as tag/length/value tuples. Both the tag and length are a byte; the length does not include these two bytes of a header, but only the payload. Zero length values are allowed.

Client devices should ignore any tags that it doesn’t understand how to decode.

Buffered Traffic Map

• Type: 0x01
• Length: 2 bytes min

If one or more periodic devices have buffered traffic pending in the coordinator, it will insert a buffered traffic map (BTM) optional tag into the beacon. The BTM has as its first (and only mandatory) value a 16-bit value N that contains the periodic device id of the first (lowest) device with buffered traffic.

If there are any more devices with pending traffic, the message will be larger than this 16-bit quantity; the rest of the message is interpreted as a bitmap, where bit 0 of byte 0 corresponds to device N+1. If a bit is set, that device has pending messages.