ABC: A Simple Explicit Congestion Controller for Wireless Networks

We propose Accel-Brake Control (ABC), a simple and deployable explicit congestion control protocol for network paths with time-varying wireless links. ABC routers mark each packet with an "accelerate" or "brake", which causes senders to slightly increase or decrease their congestion windows. Routers use this feedback to quickly guide senders towards a desired target rate. ABC requires no changes to header formats or user devices, but achieves better performance than XCP. ABC is also incrementally deployable; it operates correctly when the bottleneck is a non-ABC router, and can coexist with non-ABC traffic sharing the same bottleneck link. We evaluate ABC using a Wi-Fi implementation and trace-driven emulation of cellular links. ABC achieves 30-40% higher throughput than Cubic+Codel for similar delays, and 2.2X lower delays than BBR on a Wi-Fi path. On cellular network paths, ABC achieves 50% higher throughput than Cubic+Codel

Faster Algorithms for Dynamic Algebraic Queries in Basic RSMs with Constant Treewidth

Interprocedural analysis is at the heart of numerous applications in programming languages, such as alias analysis, constant propagation, and so on. Recursive state machines (RSMs) are standard models for interprocedural analysis. We consider a general framework with RSMs where the transitions are labeled from a semiring and path properties are algebraic with semiring operations. RSMs with algebraic path properties can model interprocedural dataflow analysis problems, the shortest path problem, the most probable path problem, and so on. The traditional algorithms for interprocedural analysis focus on path properties where the starting point is fixed as the entry point of a specific method. In this work, we consider possible multiple queries as required in many applications such as in alias analysis. The study of multiple queries allows us to bring in an important algorithmic distinction between the resource usage of the one-time preprocessing vs for each individual query. The second aspect we consider is that the control flow graphs for most programs have constant treewidth. Our main contributions are simple and implementable algorithms that support multiple queries for algebraic path properties for RSMs that have constant treewidth. Our theoretical results show that our algorithms have small additional one-time preprocessing but can answer subsequent queries significantly faster as compared to the current algorithmic solutions for interprocedural dataflow analysis. We have also implemented our algorithms and evaluated their performance for performing on-demand interprocedural dataflow analysis on various domains, such as for live variable analysis and reaching definitions, on a standard benchmark set. Our experimental results align with our theoretical statements and show that after a lightweight preprocessing, on-demand queries are answered much faster than the standard existing algorithmic approaches

DBO: Response Time Fairness for Cloud-Hosted Financial Exchanges

In this paper, we consider the problem of hosting financial exchanges in the cloud. Financial exchanges require predictable, equal latency to all market participants to ensure fairness for various tasks, such as high speed trading. However, it is extremely difficult to ensure equal latency to all market participants in existing cloud deployments, because of various reasons, such as congestion, and unequal network paths. In this paper, we address the unfairness that stems from lack of determinism in cloud networks. We argue that predictable or bounded latency is not necessary to achieve fairness. Inspired by the use of logical clocks in distributed systems, we present Delivery Based Ordering (DBO), a new approach that ensures fairness by instead correcting for differences in latency to the participants. We evaluate DBO both in our hardware test bed and in a public cloud deployment and demonstrate that it is feasible to achieve guaranteed fairness and sub-100 microsecond latency while operating at high transaction rates

Faster Algorithms for Algebraic Path Properties in Recursive State Machines with Constant Treewidth

Interprocedural analysis is at the heart of numerous applications in programming languages, such as alias analysis, constant propagation, etc. Recursive state machines (RSMs) are standard models for interprocedural analysis. We consider a general framework with RSMs where the transitions are labeled from a semiring, and path properties are algebraic with semiring operations. RSMs with algebraic path properties can model interprocedural dataflow analysis problems, the shortest path problem, the most probable path problem, etc. The traditional algorithms for interprocedural analysis focus on path properties where the starting point is fixed as the entry point of a specific method. In this work, we consider possible multiple queries as required in many applications such as in alias analysis. The study of multiple queries allows us to bring in a very important algorithmic distinction between the resource usage of the one-time preprocessing vs for each individual query. The second aspect that we consider is that the control flow graphs for most programs have constant treewidth. Our main contributions are simple and implementable algorithms that support multiple queries for algebraic path properties for RSMs that have constant treewidth. Our theoretical results show that our algorithms have small additional one-time preprocessing, but can answer subsequent queries significantly faster as compared to the current best-known solutions for several important problems, such as interprocedural reachability and shortest path. We provide a prototype implementation for interprocedural reachability and intraprocedural shortest path that gives a significant speed-up on several benchmarks

Congestion Control in Highly Variable Networks

Modern applications place an enormous demand on networks to deliver high throughput and low delay. To support applications, computer networks are evolving rapidly. Several new network environments such as datacenter and wireless networks have emerged recently and become prominent. While bandwidth has been increasing steadily in these network environments, they also exhibit significant variability in network conditions. For example, the capacity of a cellular link varies with time. Deployed congestion control solutions struggle to adapt to these variations, and their performance is far from optimal in many environments: the feedback used by these schemes is often imprecise or fails to capture variations in the network conditions fast enough. To improve performance, we need accurate and timely feedback. To this end, we advocate designing separate feedback mechanisms tailored specifically to the nuances of each network environment. Understanding how conditions are varying in each environment can help us unravel what kind of information about the network conditions can improve adaption to such variations. Additionally, the feedback mechanism should be practical and only involve changes that are within the administrative and hardware constraints of the given network environment. Following this philosophy, this dissertation contributes separate high performance congestion control solutions for three prominent network environments: (1) Wireless Networks; (2) Datacenter Networks; (3) Wide-area Internet. ABC is a simple explicit congestion control protocol for network paths with wireless links. ABC adapts to variations in the link capacity quickly and accurately. Compared to deployed schemes, ABC either achieves 50% higher throughput for similar delays or 3× lower delays for similar throughput. BFC is a practical per-hop per-flow flow control architecture for datacenter networks with bursty traffic. Compared to deployed schemes, BFC responds to congestion faster, and achieves 2.3 - 60× lower tail latency for short flows and 1.6 - 5× better average completion time for long flows. Nimbus proposes a new feedback mechanism, elasticity detection, to robustly characterize the nature of cross-traffic competing a flow. Nimbus enables low delay congestion control in the Internet without any router modifications. Compared to deployed schemes, Nimbus achieves 40-50 ms lower delays in the Internet for similar throughput.Ph.D