telecommunications traffic are described. This work has occurred as part of the WAND project which aims to provide large and reliable teletraffic traces. It is argued that to achieve this, special purpose hardware as well as careful attention to the details of measurement are required. The design of a series of measurement boards operating up to OC-48 is detailed. Experiences with using these boards are described and contrasted with experiences using software based measurement on standard PCs. The uses to which the traces are put are briefly alluded to and lessons for the measurement process drawn from them. The conclusion drawn from our experiences is that standard hardware and operating systems have fundamentally different aims from measurement and can only be used if great care is taken.