New network QoS measures for FEC-based audio applications on the Internet

New network QoS (quality of service) measures for interactive audio applications using FEC (forward error control) are proposed. Applications such as an Internet phone require both low data loss and a short delay for the underlying transport layer. The FEC-based error control has become popular as a way of meeting such requirements; new application data (or highly compressed data) are copied onto successive packets, so that random packet losses in networks can be concealed to some extent. From the viewpoint of FEC-based applications, actual QoS depends not only on the loss and delay of each packet, but also on the loss and delay of successive packets. Conventional network QoS measures such as loss rate and delay distribution, however, only focus on each packet. Therefore, the probability of long successive losses, for example, cannot be monitored, even though they strongly affect FEC-based application QoS. We propose a new concept named "loss window size" for measuring the QoS of successive packets. Definitions of loss and delay are generalized using this concept. These definitions take the FEC-based error concealment into account. Therefore, these measures enable more precise estimation of FEC-based application-level QoS than conventional measures. In order to show the effectiveness of the proposed measures, we have built an experimental monitoring system on working networks. The actual data show that network QoS may vary from time to time in terms of newly defined measures, even though QoS variation using conventional measures are not so apparent. We also model FEC-based application QoS, and show that application QoS and proposed network measures correspond well.