Delay-Constrained Input-Queued Switch

TL;DR

This paper investigates delay-constrained input-queued switches, focusing on capacity, scheduling policies, and utility maximization, introducing new methods to characterize capacity and design optimal policies for real-time applications.

Contribution

It presents three approaches—MDP, combinatorial, and Lyapunov optimization—to address fundamental problems in delay-constrained switches, including capacity characterization and optimal scheduling.

Findings

New capacity region characterization with polynomial constraints

Feasibility/throughput-optimal scheduling policy designed

Approaches applicable to various traffic patterns

Abstract

In this paper, we study the delay-constrained input-queued switch where each packet has a deadline and it will expire if it is not delivered before its deadline. Such new scenario is motivated by the proliferation of real-time applications in multimedia communication systems, tactile Internet, networked controlled systems, and cyber-physical systems. The delay-constrained input-queued switch is completely different from the well-understood delay-unconstrained one and thus poses new challenges. We focus on three fundamental problems centering around the performance metric of timely throughput: (i) how to characterize the capacity region? (ii) how to design a feasibility/throughput-optimal scheduling policy? and (iii) how to design a network-utility-maximization scheduling policy? We use three different approaches to solve these three fundamental problems. The first approach is based on Markov Decision Process (MDP) theory, which can solve all three problems. However, it suffers from the curse of dimensionality. The second approach breaks the curse of dimensionality by exploiting the combinatorial features of the problem. It gives a new capacity region characterization with only a polynomial number of linear constraints. The third approach is based on the framework of Lyapunov optimization, where we design a polynomial-time maximum-weight T-disjoint-matching scheduling policy which is proved to be feasibility/throughput-optimal. Our three approaches apply to the frame-synchronized traffic pattern but our MDP-based approach can be extended to more general traffic patterns.