Abstract: Automatic path protection switching in a synchronous optical network is tested by reference to test messages carried in section trace (J0), path trace (J1) and/or lower-order path trace (J2) sequences.

Abstract: A source unit attached to one point of a packet-switched network under test generates a stream of test packets and transmits the stream of test packets to an analysis unit attached to another point in the network. A service disruption is detected by detecting anomalous packet(s), and a service disruption time is measured by determining the time between the last packet before the disruption, and the first packet after service restoration.

Abstract: Measurement of duration of service disruption affecting communication of a data stream containing payload data and non-payload symbols interspersed within the payload data is accomplished by monitoring the data stream to detect a symbol having a value indicative of occurrence of an error in the payload data. Upon detection of a symbol having a value indicative of occurrence of an error, monitoring continues for the occurrence of errors in a modified version of the data stream, the modified version comprising the received data stream with the detected symbol omitted. An error is determined to have occurred if another symbol having a value indicative of occurrence of an error is detected in the modified version of the data stream after the omitted symbol. The duration of service disruption is taken as being the elapsed time between commencement of disruption of reception and the last determination of occurrence of an error in the modified version of the data stream.