Loop-Free Backpressure Routing Using Link-Reversal Algorithms

TL;DR

This paper introduces loop-free backpressure routing policies that use link-reversal algorithms to support feasible traffic demands while reducing delays caused by loops, demonstrated through simulations.

Contribution

It develops a joint link-reversal and backpressure routing algorithm that ensures loop-free operation and improves delay performance over classical backpressure routing.

Findings

DAG supporting a given traffic demand can be found after finite link-reversal iterations.

The LFBP algorithm improves delay performance compared to classical backpressure.

Multicommodity LFBP outperforms traditional backpressure in delay metrics.

Abstract

The backpressure routing policy is known to be a throughput optimal policy that supports any feasible traffic demand in data networks, but may have poor delay performance when packets traverse loops in the network. In this paper, we study loop-free backpressure routing policies that forward packets along directed acyclic graphs (DAGs) to avoid the looping problem. These policies use link reversal algorithms to improve the DAGs in order to support any achievable traffic demand. For a network with a single commodity, we show that a DAG that supports a given traffic demand can be found after a finite number of iterations of the link-reversal process. We use this to develop a joint link-reversal and backpressure routing policy, called the loop free backpressure (LFBP) algorithm. This algorithm forwards packets on the DAG, while the DAG is dynamically updated based on the growth of the queue backlogs. We show by simulations that such a DAG-based policy improves the delay over the classical backpressure routing policy. We also propose a multicommodity version of the LFBP algorithm, and via simulation we show that its delay performance is better than that of backpressure.