Fast Pair requires an additional channel for a persistent connection with the Providers to support Fast Pair extensions. When the Provider connects to a supported Seeker, the Seeker will attempt to connect the message stream.
Supported Implementation
Fast Pair supports two kinds of message stream implementations:
RFCOMM
Use fixed UUID as the endpoint
df21fe2c-2515-4fdb-8886-f12c4d67927c
L2CAP
Use GATT PSM Characteristic to obtain the PSM value for L2CAP connection.
Message Format
Once connected, messages can be exchanged in the following format:
| Octet | Data Type | Description | Mandatory? |
|---|---|---|---|
| 0 | uint8 | Message group | Mandatory |
| 1 | uint8 | Message code | Mandatory |
| 2 - 3 | uint16 | Additional data length | Mandatory |
| 4 - n | Additional data | Optional |
The additional data length and additional data fields should be big endian.