Caliper: Precise and Responsive Traffic Generation using NetThreads∗

This paper presents (i) Caliper, a highly-accurate packet injection tool, and (ii) NetThreads, a new platform that dramatically simplifies the development of low-level network applications on the NetFPGA board. NetThreads provides a familiar environment to software developers where multithreaded C programs can be compiled and run on the NetFPGA. On top of NetThreads, we have built Caliper, a precise and responsive traffic generator that takes packets generated on a host computer and transmits them onto a gigabit Ethernet network with precise inter-transmission times. For packet injection, existing software traffic generators rely on generic Network Interface Cards which, as we demonstrate, do not provide high-precision timing guarantees. Hence performing valid and convincing experiments becomes difficult or impossible in the context of time-sensitive network experiments. Our evaluation shows that Caliper is able to reproduce packet inter-transmission times from a given arbitrary distribution while capturing the closed-loop feedback of TCP sources. Specifically, we demonstrate that Caliper provides three orders of magnitude better precision compared to commodity NIC: with requested traffic rates up to the line rate, Caliper incurs an error of 8 ns or less in packet transmission times. Furthermore, we explore Caliper’s ability to integrate with existing network simulators to project simulated traffic characteristics into a real network environment. Caliper and NetThreads are both freely available online [1].