Assessment of VoIP Service Availability in the Current Internet

We evaluate the availability of voice over IP (VoIP) service typically achieved in the current Internet. Service availability is examined using several metrics, including call success probability, overall packet loss probability, the proportion of time the network is suitable for VoIP service, and call abortion probability induced by network outages. Our major findings are: first, packet losses are not rare events, and it is generally worse on international paths. Secondly, network outages make up a non-negligible portion of packet losses. While most outages are short, some are extremely long and make up the majority time of all outages. This implies when a service becomes unavailable, the Mean Time To Restore (MTTR) can sometimes be very high. About one third of the outages happen in symmetry, and outages tend to occur at the edges rather than in the middle of the network. Thirdly, although research networks such as Internet2 has much lower delay and loss than the public Internet, the effect of network outages on both types of networks is almost the same. Finally, we will show that when considering calls aborted due to network outages, the overall service availability drops by a significant margin, from about 99.5% to 98%.