4 magic bytes, 1 byte version, 1 byte type, 2 bytes extra, 2 bytes frame length.

MaxFrameSize is the maximum size that a single frame can be, including all headers.

TODO: what should this be for the network visibility horizon to be what we desire? ie.

MaxPayloadSize is the maximum size that a single frame can contain as a payload, not including headers.

protocol frame, forwarded using SNEK.

protocol frame, direct to peers only.

traffic frame, forwarded using tree or SNEK.

protocol frame, bypasses queues.

protocol frame, special broadcast forwarding.