Accurate packet-by-packet measurement and analysis of video streams across an Internet tight link

摘要

The response to a video stream across an Internet end-to-end path particularly depends on the performance at the path's tight link, which can be examined in a simple network testbed. A packet-by-packet (PbP) measurement methodology applied to tight link analysis requires a real-time operating system to gain the desired timing resolution during traffic generation experiments. If, as is common for other purposes, the analysis was simply in terms of average packet rate per second, no burst pattern would be apparent, and without packet-level measurement of instantaneous bandwidth the differing overheads would not be apparent. An illustrative case study, based upon the H.263+video codec, confirms the advantage of the PbP methodology in determining received video characteristics according to packetization scheme, inter-packet gap, router response, and background traffic. Tests show that routers become unreliable if the packet arrival rate passes a critical threshold, one consequence of which is that reported router processor load also becomes unreliable. Video stream application programmers should take steps to reduce packet rates and aggregate packet rates may be reduced through network management. In the case study, a burst of just nine packets increased the probability of packet loss, while the video quality could be improved by packing at least two slices into a packet. The paper demonstrates that an appropriate packetization scheme has an important role in ensuring received video quality, but a physical testbed and a precise measurement methodology are needed to identify that scheme.