Agilent Technologies, Inc.

Simon Love

Patrick Goldsack

Graham S Pollock

Brian Woodroffe

Evan Randy Kirshenbaum

James W Davis

David Moir Archibald

Jeremy Peter William Brown

Retransmission of packets in a TCP network is measured by monitoring packets traversing bearer links between nodes and examining the sequence number within its connection of each packet. For each TCP connection being monitored a next expected sequence number (NESN) value is maintained and compared with the actual sequence number of a packet in that connection. If the sequence number is less than the NESN, a retransmission count is incremented by the size of the retransmitted TCP payload; if it is greater than the NESN, a loss counter is incremented by the size of the lost TCP payload. The resulting counts of the lost and retransmitted TCP payload, of the lost and retransmitted packets, enable accurate measurements to be made even at a point remote from the sending node. Comparison of counts from spaced points in a network can enable the location of a fault to be determined at least approximately.

Measuring efficiency of data transmission

Service detail records (SDRs) are generated for at least two layers in a stack of protocols used in a communications network, where protocol data units (PDUs) for a lower-level protocol encapsulate PDUs for a higher-level protocol. SDRs for the higher-level protocol include pointers to SDRs for connections at the lower level which encapsulate PDUs from which the higher-level SDRs were generated.

Service detail records for layered communications protocols

A system and method for automatically monitoring communications networks and for determining network configuration use data stream characterizations. The system comprises a plurality of measurement probes that passively probe the network and collect data packets carried by data streams in the network. The system further comprises characterization computational units that process the collected data packets and produce data stream characterizations from the collected data packets. The data stream characterizations represent individual data streams in an arbitrarily unique manner. The system still further comprises a configuration processing unit that compares data stream characterizations taken at different points in the network and determines data stream paths through the network based on data stream characterization matching. The method for automatically monitoring communications networks comprises the steps of passively probing the data streams to produce sets of collected data packets from the data streams, determining data stream characterizations from the collected data packets, and comparing the data stream characterizations to one another to identify matching characterizations.

System and method for monitoring communication networks using data stream characterization

Data cells traversing an Asynchronous Transfer Mode (ATM) network ( ) are passively monitored by probes at two spaced points ( ). 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 ( ). 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.

Measuring network performance parameters in data communication networks

A method of synchronizing the operation of a plurality of measurement probes enables multi-point measurements of a communications network. The method comprises the step of collecting data packets from a data stream of the communications network using the plurality of probes. The data packets are collected after a predetermined start time. The method further comprises the steps of determining a hash value array from an invariant portion of the sampled data packets, and comparing the hash value array to a start hash mask. Collection by a probe of a data packet that produces a hash value array that matches the start hash mask is used as a synchronization event. The method of the present invention allows multiple measurement probes observing the same data stream at different physical locations to be synchronized such that all of the probes observe the same set of packets being carried by the data stream. The method also allows statistical control over the frequency of packet matches within a data stream to the start hash mask. Moreover, the method of the present invention depends only on passive access to the physical links of the network. As such it will not degrade the performance or availability of the network.

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Edinburgh, United Kingdom

Simon Love