Age of Information in Unreliable Tandem Queues

TL;DR

This paper develops an analytical framework to evaluate the age of information in unreliable tandem queue systems, accounting for node failures and their impact on data freshness in real-time networks.

Contribution

It introduces new models for AoI in unreliable tandem queues, extending existing reliability assumptions to more realistic scenarios with node failures.

Findings

Derived the sojourn time distribution for unreliable M/M/1 tandem systems.

Extended analysis to M/G/1 systems with multiple unreliable nodes.

Numerical results show how system parameters affect average AoI.

Abstract

Stringent demands for timely information delivery, driven by the widespread adoption of real-time applications and the Internet of Things, have established the age of information (AoI) as a critical metric for quantifying data freshness. Existing AoI models often assume multi-hop communication networks with fully reliable nodes, which may not accurately capture scenarios involving node transmission failures. This paper presents an analytical framework for two configurations of tandem queue systems, where status updates generated by a single sensor are relayed to a destination monitor through unreliable intermediate nodes. Using the probability generating function, we first derive the sojourn time distribution for an infinite-buffer M/M/1 tandem system with two unreliable nodes. We then extend our analysis to an M/G/1 tandem system with an arbitrary number of unreliable nodes, employing the supplementary variable technique while assuming that only the first node has an infinite buffer. Numerical results demonstrate the impact of key system parameters on the average AoI in unreliable tandem queues with Markovian and non-Markovian service times.