VoIP Playout Buffer Adjustment using Adaptive Estimation of Network Delays

The poor quality of Voice over IP can be improved by adaptive playout buffering at the receiver. This technique dynamically adapts the playout deadline to network conditions, thus minimizing both late packet loss and buffering time. A standard playout buffer strategy uses an estimate (Exponentially Weighted Moving Average) of the mean and variance of network delay to set the playout deadline. This estimation is characterized by a fixed, constant weighting factor. We show that tuning of this parameter so that the strategy works very well for all network conditions is not feasible. Therefore we propose to extend this standard buffer strategy by replacing the fixed, constant weighting factor with a dynamic one. In our solution, the weighting factor is dynamically adjusted according to the observed delay variations. When these variations are high (which implies that the network conditions are changing), the parameter is set low, and vice-versa. This allows rapid adaptation to network variations and reduces the frequency of late packets (or buffering time). Simulations and experimental results show that with our strategy, the trade-off between buffering delay and late packet loss at the receiver is improved significantly.