Abstract: Data cells traversing an Asynchronous Transfer Mode (ATM) network (10) are passively monitored by probes at two spaced points (12,14). A filtering characteristic is applied to select cells comparatively infrequently, and timestamps or sequence numbers (or both) for the cells selected at each point are forwarded to a correlator (28). The correlator identifies similarities in the temporal patterns of intervals between timestamps received from each probe, and uses these similarities to identify and correlate timestamps relating to occurrence of the same cell at the two monitored points. The correlated timestamps are used to determine parameters indicative of the performance of the network, such as one-way delay, variation in that delay, and rate of cell loss.

Abstract: A method and apparatus for monitoring traffic in telecommunications networks, in particular applied to the problem of recognizing real-time traffic such as voice traffic in packet- or cell-based networks through network traffic characterization. The method classifies data traffic in a packet-based communications network conveying different classes of data through the monitoring of data traffic so as to identify sequences of data packets of unknown class transmitted between a source address and a destination address, subsequently measuring parameters of at least a significant part of the packet sequence and deriving from the measured parameters a probable classification of the data conveyed in the packet sequence.