An Analysis of Dynamic Flow Scheduling for Data Center Networks An analysis of the paper “ Hedera : Dynamic Flow Scheduling for Data Center Networks ” [ 1 ]

This paper provides an analysis of the article “Hedera: Dynamic Flow Scheduling for Data Center Networks” [1] and the related subject matter (“Hedera” and/or “Hedera’s” henceforth). Written in 2010, “Hedera’s” goal is to optimize dynamic flow scheduling in data centers. In short, “Hedera” presents: “[A] scalable, dynamic flow scheduling system that adaptively schedules a multistage switching fabric to efficiently utilize aggregate network resources” (see “Hedera” at Abstract). This paper provides a detailed analysis of “Hedera” in the following sections: 1. The Problems to be Solved 2. The Proposed Solutions 3. Strengths of the Proposed Solutions / Effectiveness 4. Weaknesses of the Proposed Solutions / Additional Considerations 5. Conclusion Overall, “Hedera” proves effective based on solid simulation and testbed results for a given set of assumptions and constraints (e.g. large flows, commodity switches, packet transmission dynamics, etc.). The solid simulation results indicate that “Hedera’s” performance is 96% of optimal (e.g. as compared to non-blocking throughput) and a 113% improvement over ECMP static hashing [2]. Further, “Hedera’s” testbed results outperformed ECMP in a wide variety of test cases. Thus, “Hedera” appears to be effective in (1) paving the way for improved dynamic flow scheduling for data center networks and (2) opening up new possibilities for additional research to obtained even better dynamic flow scheduling performance within data center networks. 1. The Problems to be Solved “Hedera” provides an analysis of the problems confronting “Dynamic Flow Scheduling for Data Center Networks” (id. at Title). The problems confronting data center networks include: 1. Data center designers have no way of knowing how data center network demand and workloads will vary over time, thus designers need a dynamic solution that can adapt over time. 2. The data center network system must operate using commercially available commodity system components without requiring protocols and/or software changes. 3. Inter-rack network bottlenecks caused by virtualization technology [3] including separate physical servers used to multiplex customers across multiple machines make it difficult to ensure the virtualization instances will run on the same physical rack. The above problems are compounded by the fact that multi-rooted tree like networks structures provide many paths between host pairs, yet have decreasing aggregate bandwidth when moving up to the top of the hierarchical tree structure. At the time “Hedera” was written, ECMP with static hashing [2] was a prevalent means to route data flows, yet ECMP with static hashing resulting in “collisions overwhelmed switch buffers”, thus depleted network system performance (see “Hedera” at Section 1). “Hedera” addresses the problems noted above by collecting flow information, dynamically computing non-conflicting paths for the data flows, and then programming commodity switches to reroute the traffic according to the newly computed non-conflicting paths.