[time-nuts] Good references on holdover?

[Javier Serrano]

Dear all,

We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?

Thanks!

Javier

[1] http://www.ohwr.org/projects/white-rabbit/wiki