Abstract
The overlay approach has been widely used by many service
providers for traffic engineering in large Internet backbones. In the
overlay approach, logical connections are set up between edge nodes to
form a full mesh virtual network on top of the physical topology. IP
routing is then run over the virtual network. Traffic engineering
objectives are achieved through carefully routing logical connections
over the physical links. Although the overlay approach has been
implemented in many operational networks, it has a number of well-known
scaling issues. This paper proposes a new approach, which we call the
integrated approach, to achieve traffic engineering without full-mesh
overlaying. In the integrated approach, IP routing runs natively over
the physical topology rather than over the virtual network. Traffic
engineering objectives are realized by setting appropriate link metrics
in IP routing protocols. We first illustrate our approach with a simple
network, then present a formal analysis of the integrated approach and a
method for deriving the appropriate link weights. Our analysis shows
that for any given set of optimal routes of the overlay approach with
respect to a set of traffic demands, the integrated approach can achieve
exactly the same result by reproducing them as shortest paths. We
further extend the result to a more generic one: for any arbitrary set
of routes, as long as they are not loopy, they can be converted to
shortest-paths with respect to some set of positive link weights. A
theoretical insight of our result is that the optimal routing (with
respect to any objective function) is always shortest path routing with
respect to some appropriate positive link weights
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