Simple alternate routing for differentiated services networks

Recent work on differentiated services in the Internet has introduced new n otions of quality of service (QoS) which apply to aggregates of traffic in networks with coarse spatial granularity. Most proposals for differentiated services involve traffic control algorithms for aggregate service levels, packet marking and policing, and preferential treatment of marked packets i n the network core. The issue of routing for enhancing aggregate QoS has no t received a lot of attention. This study investigates the potential benefi t of using multipath routing strategies in support of differentiated servic es. We propose a traffic control scheme, called simple alternate routing, w herein portions of unmarked packet flows can be assigned to alternate paths through a service provider network (SPN) in response to congestion feedbac k information. The scheme is simple, requiring only minor changes to the SP N border routers so that alternately routed packets can be tunneled via con ventional paths to an intermediate border node and then tunneled from there to the original egress border node. We present distributed algorithms for discovering congestion within the SPN and allocating traffic to alternate p aths that are uncongested. We have implemented the scheme in a packet-level simulation, and we have examined the transient response of the algorithm t o perturbations in the nominal traffic levels experienced by the SPN. The e xperimental study of this paper provides some understanding of the scheme's ability to adapt in routing packets around congestion. Our results indicat e that the multipath routing framework shows promise for aggregate QoS and warrants further consideration. (C) 2001 Elsevier Science B.V. All rights r eserved.