EXFO FTB-800 Series for FTB-1 - Manual (Page 565)

Glossary
NetBlazer 555
G.709 Optical Transport Network (OTN)
Tandem Connection Monitoring (TCM)
TCM enables the user and its signal carriers to monitor the quality of the
traffic that is transported between segments or connections in the network.
SONET/SDH allowed a single level of TCM to be configured, while ITU
G.709 allows six levels of tandem connection monitoring to be configured.
The assignment of monitored connections is currently a manual process
that involves an understanding between the different parties. There are
various types of monitored connection topologies: cascaded, nested and
overlapping. Examples of these topologies are provided in the following
figure.
Tandem Connection Monitoring