Completed PhD Student: Stephen Strowes

Congratulations to Stephen Strowes, who successfully defended his PhD thesis (on “Compact Routing for the Future Internet”) today.

The abstract of his dissertation is:

The Internet relies on its inter-domain routing system to allow data transfer between any two endpoints regardless of where they are located. This routing system currently uses a shortest-path routing algorithm (modified by local policy constraints) called the Border Gateway Protocol. The massive growth of the Internet has led to large routing tables that will continue to grow. This will present a serious engineering challenge for router designers in the long-term, rendering state (routing table) growth at this pace unsustainable.

There are various short-term engineering solutions that may slow the growth of the inter-domain routing tables, at the expense of increasing the complexity of the network. In addition, some of these require manual configuration, or introduce additional points of failure within the These solutions may give an incremental, constant factor, improvement. However, we know from previous work that all shortest-path routing algorithms require forwarding state that grows linearly with the size of the network in the worst case.

Rather than attempt to sustain inter-domain routing through a shortest-path routing algorithm, compact routing algorithms exist that guarantee worst-case sub-linear state requirements at all nodes by allowing an upper-bound on path length relative to the theoretical shortest-path, known as path stretch. Previous work has shown the promise of these algorithms when applied to synthetic graphs with similar properties to the known Internet graph, but they haven't been studied in-depth on the actual Internet graph.

In this dissertation, I demonstrate the consistently strong performance of these compact routing algorithms for inter-domain routing by performing a longitudinal study of two algorithms on the Internet Autonomous System (AS) graph over time. I then show, using the k-cores graph decomposition algorithm, that the structurally important nodes in the AS graph are highly stable over time. This property makes these nodes suitable for use as the “landmark” nodes used by the most stable of the compact routing algorithms tested, and the use of these nodes shows similar strong routing performance. Finally, I present a decentralised compact routing algorithm for dynamic graphs, and present state requirements and message overheads on AS graphs using realistic simulation inputs.

To allow the continued long-term growth of Internet routing state, an alternative routing architecture may be required. The use of the compact routing algorithms presented in this dissertation offer promise for a future Internet routing system.

Update (18 February 2012): the final version of Stephen's dissertation is now available.