A connection-oriented communications network (4) comprises a plurality of interconnected nodes (N1-N4, 11-13). A traffic path (N1-N2-N3-N4) can be set up across the network (4). Path delay data is obtained for the traffic path by using control plane signalling messages (e.g. a Resource Reservation Protocol - Traffic Engineering, RSVP-TE signalling message) between nodes of the traffic path. The path delay data can be path delay asymmetry data indicative of an asymmetry in path delay between a forward transmission direction and a reverse transmission direction of the traffic path. Each intermediate node (N2, N3, N4) along the traffic path can form a signalling message for forwarding to the downstream node which includes one or more values of path delay incurred by that node, or an accumulated path delay value. The path delay can result from one or more of mapping delay, Forward Error Correction (FEC) coding and propagation delay.