QoS routing using alternate paths

A QoS routing protocol based on alternative path selection is described. Using a combination of source routing and shortest path routing, packets are routed along alternate paths when available resources along the shortest path cannot satisfy the QoS requirements of end to end ows. For path selection, the QoS routing protocol makes use of the information already available in the OSPF link information database. Packet forwarding uses existing mechanisms within the Internet protocols. Thus, support for QoS routing is provided without requiring major changes to the existing installed base of OSPF routers. Our proposal provides QoS routes for unicast as well as multicast connections. The major virtues of the solution are that of providing an evolutionary approach, whereby only a subset of the routers need to be enabled, and that the additional algorithms are computationally simple without requiring state maintenance at every router. Simulations of our proposed routing protocols on the UUnet backbone show that they perform well, almost optimal in terms of delivering the desired QoS for end to end ows.