Rapid fault detection and recovery for IP telephony

Short, low-bandwidth keep-alive packets can be injected into VoIP packet streams to rapidly detect faults and deteriorating network conditions (e.g., increasing delay, jitter, or loss). The keep-alive packets can be duplicated and also used to continuously monitor and compare the delay and loss characteristics of primary and alternate network paths, and thereby help control the rapid switchover of calls (in-progress and future) to alternate routing paths (or the circuit-switched PSTN) when faults or deteriorating QoS conditions are detected. By simultaneously transmitting copies of keep-alive packets over multiple paths to make the differential delay measurements and comparisons, the proposed techniques avoid many common synchronization and timing errors. We examine various performance tradeoffs and describe several ways to implement the proposed architectures and techniques.