The Universal Serial Bus transmits differential data over twisted- pair cables originally designed for signaling at 12Mbit/s. Because of the recent specification of a 480Mbit/s signaling speed with the existing cabling, the high frequency behavior and temporal response of these cables is of interest. In this work, two- and three- dimensional field solvers are used to characterize the field behavior within the cables. The results are used to perform SPICE simulations of complete time-domain USB packets, which indicate that existing cables support the higher bit rates well, and that the quality of signaling is not limited by the cable construction. The simulations match well with the limited measurement data available for 480Mbit/s signaling.