acm sigcomm

Router grafting is a recently proposed technology (Keller et al., NSDI’10) that permits migrating one local endpoint of a session between two routers without having to inform the remote one. By doing so, it permits reconfiguring several aspects of an IP network without imposing downtimes or inflicting severe and potentially dangerous changes to BGP. In this paper the authors looks at the potential of putting router grafting to work for the benefit of traffic engineering. The main idea is that an optimal traffic engineering depends among others on the characteristic of the traffic matrix to be served. Router grafting allows reshaping a traffic matrix by selecting the ingress and egress points at which traffic is received and handed over to other networks. Therefore, it has the potential to improve traffic engineering by applying it on an easier to handle, reshaped traffic matrix. The authors formulate a generalized traffic engineering problem that includes the extra degree of freedom, propose two heuristics for solving it, and present evaluation results based on Internet2 traffic. These results point to a potential improvement of around 20% due to router grafting. An interesting paper making the case for router grafting more concrete by putting it into the context of traffic engineering and evaluating using real traffic data. The reviewers criticized almost consistently the assumption that traffic is handed over between networks over a single link, pointing to the fact that peering or customerprovider relationships typically require two networks to meet at multiple points. A second suggestion for improvement was to consider in the evaluation more realistic data regarding the availability of alternative points to which an existing link can be migrated (eg, factoring practical aspects like the existence of ports and circuits for moving the traffic to the new end-point). One could look, for example, at some Internet Exchange Points (IXP) and provide a more concrete quantification of benefits based and their actual tenants and the costs for moving to alternative sites. Finally, a more in-depth look at the source behind the demonstrated 20% performance gain would benefit this paper. Where does it come from? Is it connected to diurnal traffic patterns or is it a one-shot improvement that once performed requires no further alternation of inter-connection points? Overall, a solid performance evaluation work that leaves some interesting questions open for future study.