Tandem Connection Monitoring (TCM)

Tandem system is also known as cascaded systems.

SDH monitoring is divided into section and path monitoring. A problem arises when you have “Carrier’s Carrier” situation where it is required to monitor a segment of the path that passes another carrier network.

Tandem Connection Monitoring

Here Operator A needs to have Operator B carries his signal. However he also needs a way of monitoring the signal as it passes through Operator B’s network. This is what a “Tandem connection” is. It is a layer between Line Monitoring and Path Monitoring. SDH was modified to allow a single Tandem connection. ITU-T rec. G.709 allows 6.

TCM1 is used by the User to monitor the Quality of Service (QoS) that they see. TCM2 is used by the first operator to monitor their end-to-end QoS. TCM3 is used by the various domains for Intra domain monitoring. Then TCM4 is used for protection monitoring by Operator B.

There is no standard on which TCM is used by whom. The operators have to have an agreement, so that they do not conflict.

TCM’s also support monitoring of ODUk connections for one or more of the following network applications (refer to ITU-T Rec. G.805 and ITU-T Rec. G.872):

–          optical UNI to UNI tandem connection monitoring ; monitoring the ODUk connection through the public transport network (from public network ingress network termination to egress network termination)

–          optical NNI to NNI tandem connection monitoring; monitoring the ODUk connection through the network of a network operator (from operator network ingress network termination to egress network termination)