Source Routing and Scheduling in Packet Networks

TL;DR

This paper introduces an online routing algorithm that finds admissible paths in packet networks and a distributed scheduling protocol that guarantees polynomial end-to-end delays, improving network stability and performance.

Contribution

It presents the first online routing algorithm for admissible paths and a deterministic distributed scheduling protocol with polynomial delay guarantees.

Findings

The routing algorithm computes paths immediately upon packet injection using congestion-aware shortest paths.

The scheduling protocol ensures polynomial delay for all packets under deterministic, distributed implementation.

Path selection can influence network stability, with some topologies remaining stable under certain protocols regardless of adversarial path choices.

Abstract

We study {\em routing} and {\em scheduling} in packet-switched networks. We assume an adversary that controls the injection time, source, and destination for each packet injected. A set of paths for these packets is {\em admissible} if no link in the network is overloaded. We present the first on-line routing algorithm that finds a set of admissible paths whenever this is feasible. Our algorithm calculates a path for each packet as soon as it is injected at its source using a simple shortest path computation. The length of a link reflects its current congestion. We also show how our algorithm can be implemented under today's Internet routing paradigms. When the paths are known (either given by the adversary or computed as above) our goal is to schedule the packets along the given paths so that the packets experience small end-to-end delays. The best previous delay bounds for deterministic and distributed scheduling protocols were exponential in the path length. In this paper we present the first deterministic and distributed scheduling protocol that guarantees a polynomial end-to-end delay for every packet. Finally, we discuss the effects of combining routing with scheduling. We first show that some unstable scheduling protocols remain unstable no matter how the paths are chosen. However, the freedom to choose paths can make a difference. For example, we show that a ring with parallel links is stable for all greedy scheduling protocols if paths are chosen intelligently, whereas this is not the case if the adversary specifies the paths.