Algorithms and protocols for stateless constrained-based routing

Quality of service (QoS) routing has generally been addressed in the context of reservation-based network services (e.g. ATM, IntServ), which require explicit (out of band) signaling of reservation requests and maintenance of per-flow state information. It has been recognized that the processing of per-flow state information poses scalability problems, especially at core routers. To remedy this situation, in this paper we introduce an approach for stateless QoS routing in IP networks that assumes no support for signaling or reservation from the network. Instead, our approach makes use of the currently unused two bits in the DiffServ (DS) byte of the IP packet header. Simple heuristics are used to identify a low-cost delay-constrained path. These heuristics essentially divide the end-to-end path into at most two ‘superedges’ that are connected by a ‘relay node’. Routers that lie on the same superedge use either the cost metric or the delay metric (but not both) to forward the packet. Standard hop-by-hop forwarding is performed with respect to either metric. Two different approaches are presented for implementing the relay-based forwarding. In the first approach, a probing protocol is used to identify the relay node and the routing metrics of the superedges. Tunneling and packet encapsulation are then used to forward packets from the source node to the relay node and then from the relay node to the destination node. The second approach does not require probing, but instead relies on the time-to-live (TTL) field in the header of the IP packet. Simulations are presented to evaluate the cost performance of the various approaches. q 2002 Elsevier Science B.V. All rights reserved.