User manual

Appendix A

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

ETC

Fibe

ETC