A telecommunications transport network is described in which a plurality of network elements each has a performance monitoring facility operative to report overall error rate at the element in each network path using the element. The network includes one or more management systems operative to calculate performance of a segment of a path between two network elements, from the reported overall error rates at the elements. Monitoring can thus be provided in management software using standard interfaces to gather the reported error rates, without additional ASICs at the network elements. Since not all paths will require TCM the additional processing required by the network management systems need not be great. Not even every connection that crosses a domain boundary will necessarily need TCM although the facility is especially useful for dedicated connections.