1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +---------------+---------------+-------------------------------+ | Next Payload |C| RESERVED | Payload Length | +---------------+---------------+-------------------------------+ | Protocol ID | SPI Size | Notify Message Type | +---------------+---------------+-------------------------------+