[ntpwg] REQUEST FOR TEXT - Protocol Doc Changes

[Stewart Bryant]

My first thought was that the timing reference point
should be the first bit of the NTP payload, since
this was within the NTP scope and everything before it
was a variable length.

However on reflection after reading the thread I think
that the only point in the packet that you can rely
on is start of frame, and this is by far the
easiest point in the frame for the receive hardware
to capture and locally timestamp.

The variable number of bits in the datalink header
and the IP header (IPv4/v6) in principle be
corrected because

a) Both transmitter and receive know (at least in
principle) how many there are and can apply corrections

b) If you go through some switching equipment that
changes any of these factors, then in general
the errors introduced by the switching will
be significant compared to this error, although
in principle the switches could correct the timestamp
accordingly as part of some sort of one step
transparent clock.

- Stewart