Characterizations or models of electrical networks assist designers in predicting how a network will perform in a proposed system without physically constructing the complete system. This allows engineers to quickly test, by simulation, various options and thereby reduce design costs and schedules. For linear networks, characterizations may be obtained from measurements made at the network ports. These models are commonly developed in the frequency domain; such models can be applied directly in frequency-domain simulation and indirectly in time-domain simulation. Alternatively, measurements taken at the ports can also be used to develop time-domain models that are directly applicable for time-domain simulation. This alternate approach has the advantages of avoiding sometimes-difficult transformations and requiring only time-domain instrumentation.