ISPs as nodes or sets of links?

We consider the contract-switching paradigm for studying the inter-domain traffic engineering problem. In the contract-switching paradigm, each ISP in the Internet is abstracted as a set of edge-to-edge contract links. We formulate the optimal routing problem for the contract-switching paradigm by considering three objectives, namely: 1) maximizing throughput, 2) minimizing delay, and 3) minimizing bandwidth usage. We solve the optimization problems on realistic network topologies and show that the routing solutions developed using the contract-switching paradigm provides significant improvement in performance compare to the BGP routing framework with respect to the three objectives. Moreover, our simulation study also reveals that the contract-switching paradigm performs close to the best performance that can be achieved in the Internet in the absence of any abstractions.