CTC Union FRM220-NMC, User Manual, Page: 114 / 182

Appendix A
112
Clocking Modes
There are three clocking schemes for the FRM-DATA converters, shown below.
Int.
Recovery
Ext.
Recovery
Transparent
Transparent
Figure A-? FRM-DATA Clocking Modes
All models of the FRM220-DATA have a physical interface which is DCE. A crossover cable is required when
acting as a DTE device. In the first example, the units act as 'Fiber Modems' with the internal clocking unit acting as
a master time source and the remote or loop unit recovering timing from the fiber side. In this configuration, both
units are acting as DCE.
In the second example, an external clock is received at one unit and the clock is passed to the remote for
recovery via the fiber. In this scheme, the left side unit acts as a DTE and a crossover cable is required. The right
hand unit recovers clock from the fiber and acts as a DCE.
In our last example, transparent clocking is employed; the transmit clock on one side is used as the source for
receive clock on the other. In this scheme the units may act as DCE or DTE depending on the cable used.
Fibe
T T
RC RC
Fibe
T
RC
ETC
Fibe
ETC RC
ETC RC