Effects of channel delays on underflow events of compressed video over the Internet

This paper presents an extensive statistical study and analysis of the effects of channel delays in the current (best-effort) Internet on underflow events in MPEG-4 video streaming. Two types of network delays are considered: end-to-end round-trip delays and delay jitter. Our data were collected in a seven-month real-time streaming experiment, which was conducted between a number of unicast dialup clients in more than 600 major USA cities and a backbone video server. Among other findings, our analysis shows that startup delays approximately 15-20 times the average roundtrip time (RTT) are required for the client to avoid 90% of late packets caused by delay jitter. Meanwhile, startup delays of only 3-4 times the average RTT are needed to achieve lost-packet recovery rates of 90% or more. Hence, a key finding of our study is that delay jitter represents a more challenging problem for video streaming applications than round-trip delays. We also show that the probability density function (PDF) of RTT samples, which are associated with retransmitted video packets, can be modeled using a Pareto distribution. This observation indicates that the upper tail of the RTT PDF decays slower than reported in earlier studies.