Measuring and comparing performance of an Internet multimedia signaling protocol across varying vendor implementations is a challenging task. Tests to measure the performance of the protocol as it is exhibited on a vendor device and conditions of the laboratory setup to run the tests have to be normalized such that no special favour is accorded to a particular vendor implementation. In this paper, we describe a performance benchmark to measure the performance of a device that includes a Session Initiation Protocol (SIP) proxy function. This benchmark is currently being standardized by the Internet Engineering Task Force (IETF). We implemented the algorithm that has been proposed in the IETF to measure the performance of a SIP server. We provide the test results of running the benchmark on Asterisk, the popular open source SIP private branch exchange (PBX).