Automatic fault detection and recovery in real time switched Ethernet networks

EtheReal is a real-time fast Ethernet switch architecture that provides bandwidth guarantees to distributed multimedia applications without OS or hardware modifications on the host machines. It implements true link-layer multicast, and offers a natural match to support network-layer QoS protocols such as RSVP. Because real-time performance guarantees fundamentally require state to be installed inside the network, link/switch failures could lead to significant disruption to the QoS promised to the user applications. This paper describes the fault detection and recovery mechanism supported by the EtheReal architecture, and reports on the performance measurements of the initial prototype implementation. The heart of EtheReal's fault detection and recovery mechanism is a fast spanning tree reconfiguration algorithm to reduce the total fault recovery time, and a delayed link inactivation scheme that allows real-time connections which are not affected by the failed links/switches to continue to exist, even though some of the links are marked as "blocked" in the new spanning tree topology. Measurements on the prototype show that the fault detection and recovery time on a network whose diameter is 10 hops are 220 ms and 31 ms, respectively. This combined delay corresponds to a minor jitter in real-time audio/video communication, and is a significant improvement over the standard IEEE 802.1d implementation, which takes on the order of 30 sec.