OptionalackWhere the relay's acknowledgment would arrive, or null ahead of a join request,
which no relay acknowledges.
The relay window, timed from the end of the uplink like the other two.
When the uplink itself goes out, in microseconds, whether or not the acknowledgment arrives.
The frame that wakes the relay.
The wake-on-radio exchange an uplink under a relay goes out behind, TS011-1.0.1 section 5.