Abstract: An international telecommunications network includes a set of international exchanges located in a particular country which connect a national telecommunications network situated in that country with networks situated in other countries. The international network includes a traffic management system having an expert system with a set of knowledge sources. An identifier identifies alarms relating to traffic and a prioritizer arranges the alarms in order of priority. A diagnoser diagnoses the cause or causes of the alarms by proposing suspected causes and investigating them in relation to traffic and network data. A resolver proposes remedies for the causes of the alarms by reasoning over each cause in relation to data on traffic associated with the cause, reasoning over each remedy in relation to data on traffic in the neighborhood of the remedy to determine a figure of merit for the remedy, and then arranging the remedies in order of merit.

Abstract: A semiconductor laser amplifier includes both a waveguide layer and an active layer. In use, an optical wave in the active layer interacts with the waveguiding layer to reduce the polarisation sensitivity of the amplifier. A short, thick active layer is not required, typical dimensions being 250 or 500 .mu.m long, by 0.2 .mu.m high. The mesa is typically about 2 .mu.m wide, but may be wider.