Measurement of round-trip delay or travel time in a communications network during in-service operation is accomplished by use of two probes, situated at respective points of interest along the communication network, and a processor. The probes receive identifiable data patterns normally transmitted over...http://www.google.co.uk/patents/US5521907?utm_source=gb-gplus-sharePatent US5521907 - Method and apparatus for non-intrusive measurement of round trip delay in communications networks
