Measuring one-way delay of VoIP packets without clock synchronization

One-way network delay is a critical parameter in VoIP as it allows the application to assess the perceived quality. However, it is well known that it is very difficult to measure one-way delay of the VoIP packets traversing the network. This is because the Internet architecture is based on the end-to-end principle in which the endpoints are connected to the network independently, typically without clock synchronization. Here we propose a novel VoIP measurement methodology called Sync & Sense of Periodic Stream (SSPS) that can contribute significantly to overcome such a challenge. SSPS is the algorithm running on the receiver that monitors the timing of the arriving RTP packets. Using the information provided in the standard RTP packet, SSPS can build the transmission timing of the sender that is virtually synchronized with the reception timing. This allows SSPS to measure queuing delay which is the key component of the one-way network delay. Whereas the other delay components such as transmission and propagation delays are fixed and can be estimated, queuing delay is very critical because it is highly variable and unpredictable. Being able to measure the queuing delay enables SSPS to estimate the one-way network delay at a very high level of accuracy. Our experimental result shows that SSPS performs very well in the real-world environment.