Isdnsync was written by Andreas Eversberg. It is a small tool that initalizes a cheap HFC-S ISDN-Card so that bit and framclock are present on 2 IC-Pins. These signals can be used to feed HFC-E1 card with a very exact clock.

{{{
Usage: ./isdnsync <card>

Opens given card number in TE-mode PTP and tries to keep layer 2 established.
This keeps layer 1 activated to retrieve a steady sync signal from network.
}}}

see also: [wiki:Isdnsync] (Howto)