Abstract: An LAN parameter measuring instrument is provided for measuring at least one physical parameter of a wired, packet based, baseband LAN. The instrument comprises input means for providing a connection to the LAN transmission medium to enable measurements to be made while the LAN is active and voltage measuring means arranged to connect to the LAN transmission medium through said input means and operative to measure the voltage on the LAN transmission medium during inter-packet gaps. The instrument may determine the resistance of the LAN by measuring the inter-packet voltage during the injection of a known current into the transmission medium.

Abstract: A protocol analyzer is provided for monitoring a selected communication connection being conducted in accordance with a predetermined protocol by the exchange of protocol data units between two entities over a data network. The analyzer includes a monitoring device for identifying protocol data units, a protocol-follower conditioned in dependence on said predetermined protocol and operative to follow the progress of the connection as it receives relevant protocol data units from the monitoring device, and an alarm indicating when the sequence of protocol data units diverges from the protocol. The protocol data units are passed through a FIFO store as they are used by the protocol-follower, so that on a protocol violation occurring, the sequence of protocol data units leading up to the violation can be extracted from the FIFO store and displayed.

Abstract: A monitoring device detects late packet collision on a CSMA/CD LAN. The device comprises a first detector for detecting the presence of a packet in the LAN, a second detector for detecting the occurrence of a packet collision in the LAN and a late collision indicator which provides a late collision indication whenever the second detector detects the occurrence of a collision more than a predetermined time after the first detector detects the presence of a packet.