Mixing Compensation of DCMs Results in the Inconsistency of Channel Performance

Symptom

In a network, when signals are transmitted from site A to site B, the pre-FEC BERs of many boards are not consistent. The pre-FEC BER of channels of good performance is 0 and the pre-FEC BER of channels of the worst performance is 5.

Figure 1 Network topology of network H

Cause analysis

In a network using mixed fibers (namely, the G.652 and G.655 cables), the dispersion must be calculated by each channel. On a network with over 10 Gbit/s rate, avoid using a G.652 DCM to compensate a G.655 fiber during project design, and at the same time, ensure that performance of long-wavelength channels and short-wavelength channels meets requirements.

The cause dues to mixed dispersion compensation, not all channels can reach the optimal dispersion compensation point.