A Connectionless Approach to Intra- and Inter-Domain Traffic Engineering

Traffic Engineering (TE) deals with the task of mapping traffic flows to the routes in an existing physical topology to improve the performance of operational IP networks. A desirable traffic engineering solution must provide network operators a precise control over the traffic flows within their routing domains. This enables the network operators to provide new services by appropriately managing the traffic. Multi Protocol Label Switching (MPLS) allows explicit setup of one or more label switched paths (LSPs) between any source and destination and the traffic can be arbitrarily mapped to the available LSPs. However, MPLS uses a conn ctionorientedor signaledapproach. This requires that all routers along the LSP be upgraded to support MPLS. In MPLS, the problem of setting-up LSPs is de-coupled from the problem of optimally splitting traffic among the available LSPs. In contrast, current work in the area connectionlessintra-domain TE is to use a parametric approach. Essentially, the link weight parameter of the routing algorithm is changed to find “good” routes under quasi-stationary traffic assumption. The idea of optimizing OSPF link weights for the prevailing traffic conditions was proposed in [2], [4]. In this case, the paths on which the traffic is routed depend on traffic demands itself. This approach will hence lead to a route change for any desired change in traffic mapping or change in the demand matrix. A source-controlled traffic mapping on finer time-scales is not possible with the current connectionless TE approach, and leads to control traffic overhead (LSA re-advertisement) for every change in link weight. The routing algorithm (OSPF or IS-IS) only provides a single shortest path or multiple paths in case of Equal Cost Multi Path (ECMP) between any pair of nodes. The second approach is the multi-path approach which requires full upgrades and potential signaling. The prior work in the area of multi-path routing [3], [5], [1] have assumed support from all the routers. We propose a connectionless approach to achieve explicit source-routing along multiple-paths without using signaling. Explicit source-routing can be achieved using the proposed approach in a partially upgraded network, where only a subset of routers support the multi-path forwarding. The key idea is to capture an intra-domain path, inter-domain AS-path or an exit route from an AS as a 32-bit hash in the packet header. We demonstrate how the proposed approach can be used to achieve TE in both intraand inter-domain context with partial upgrades. Essentially, our approach trades off computational complexity to avoid signaling. We describe ways to manage the space (due to multiple paths) and computation complexity at the upgraded routers. Note that, our scheme, like MPLS, de-couples the problem of path computation from the problem of traffic splitting, i.e. the source may arbitrarily split traffic among the available paths without re-computing the paths. In this paper, we propose the connectionless building-blocks and do not address the problem of optimal (or near-optimal) traffic splitting or how these building blocks can be used to provide improved quality of service.