Generating realistic and responsive traffic that reflects different network conditions is a challenging problem associated with performing valid experiments in network testbeds. In this work, we preset Caliper, a highly precise traffic generation tool, built on NetThreads, a flexible platform that we have created for developing packet processing applications on FPGA-based devices and the NetFPGA in particular. We will demonstrate the effect of ad-hoc interdeparture times on a commodity NIC compared to precisely timed inter-departures with Caliper. Both NetThreads and Caliper are available as free software to download [1]. Categories and Subject Descriptors C.2.1 [Computer-Communication Networks]: Network Architecture and Design General Terms Design, Experimentation, Measurement Keywords NetFPGA, Traffic Generation, Soft Processors