Monitoring a synchronous digital hierarchy transmission path

摘要

here is described a system for monitoring utilisation of a tributary (17) to a main SDH transmission path (15). The main SDH transmission path is arranged to transport a series of data frames, each of which contains virtual containers. A data signal from tributary (17) is loaded into virtual containers reserved to carry the data signal. The monitoring system (20) comprises an optical service unit (21) and a computer (22). The optical service unit (21) monitors the bytes of the virtual containers reserved to carry the tributary for the presence of a predetermined bit pattern and transmits a report containing the results of the monitoring to the computer (22). In the computer (22), the data contained in the report is used to evaluate utilisation of the tributary. One example of the bit pattern which is monitored is the presence of all binary "1"s in each byte of the payload of a virtual container.