There is increasing interest in IP telephony to help lower costs and enable new services. Many enterprises and call centers are adopting IP telephony over their converged IP infrastructure and many multi-site corporations are using Voice over IP (VoIP) for their intra- and inter-site communication.
With the use of VoIP for mission-critical business applications, it is important to evaluate and improve the reliability and quality of VoIP calls. Ideally, a VoIP call should be as reliable as a traditional circuit-switched phone call. However, when monitoring and evaluating the quality of a VoIP call (especially over wide area links), it is necessary to deal with the inherent packet losses, delays, and jitter associated with IP networks, which are not encountered in traditional circuit-switched networks. Even though IP networks are largely self-healing for network faults, and many enterprise networks are engineered to have redundant links or paths between sites, today's IP networks are not engineered to react to performance degradations at the timescales needed for voice. For example, recent studies show that while there is acceptable performance within some service provider networks, many backbone paths still have poor VoIP performance and network faults cause problems.
To provide a robust VoIP infrastructure, it is important to rapidly detect performance degradations and faults. This detection is complicated by several factors. On a per-connection basis, for example, there are natural silence periods in VoIP calls during which packets are not transmitted by a source (e.g., when a participant in a call is listening rather than speaking). Consequently, while monitoring a VoIP call (e.g., on the receiving side) it is necessary to distinguish between gaps that occur due to natural speech silences and perhaps speech compression, and the gaps that occur due to packet loss, delay, and jitter in the IP network. Furthermore, although detecting problems can certainly help to alert a network manager, it would be particularly useful if the network could react to a detected problem and route around it.
Accordingly, there is a need for techniques for performing rapid fault detection and recovery in communication networks such as IP telephony networks, particularly those that provide VoIP applications.