Doctoral Speaking Skills Talks - Anup Agarwal

— 5:00pm

Location:
In Person - Reddy Conference Room, Gates Hillman 4405

Speaker:
ANUP AGARWAL , Ph.D. Student
Computer Science Department
Carnegie Mellon University
https://108anup.github.io/

Designing Congestion Control Algorithms with Performance Guarantees

Congestion control algorithms (CCAs) are a key enabler (or limiter) of the performance of networked applications on the Internet and data centers. CCAs determine the rate at which different flows should send traffic, aiming to share network resources fairly and efficiently. Despite decades of research and their performance-critical nature, CCAs are largely designed through heuristics and human intuition. As a result, our community continuously discovers new ways in which CCAs fail, i.e., exhibit severe unfairness, underutilization, or congestion. My work develops tools to formally reason about CCA performance and designs CCAs that can provably guarantee performance even under challenging network conditions.

In this talk, I will present a part of my work that introduces abstractions to reason about CCA behavior through the mechanisms that CCAs use to coordinate fairness. CCAs operate in partially observable environments: they cannot directly observe link capacities or competing flows. To share network resources fairly, CCAs (implicitly) communicate fair shares through observable signals such as delay or loss. For instance, Reno, a historically popular CCA, encodes the fair share as proportional to "1/sqrt(loss rate)". We refer to such communication mechanisms as contracts. 

I will show how the choice of contracts, one that most CCA designers do not even make explicitly, fully determines key steady-state CCA performance metrics, exposing fundamental tradeoffs between the metrics. Contracts also help understand and uncover a wide range of performance failures in past CCAs. Building on these insights, I will share some intuition behind FRCC, a new congestion control algorithm I developed that provably ensures fairness on networks where existing CCAs starve flows.

Presented in Partial Fulfillment of the CSD Speaking Skills Requirement 

For More Information:
matthewstewart@cmu.edu

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