Scheduling periodic messages on a shared link

Abstract

Cloud-RAN is a recent architecture for mobile networks where the processing units are located in distant datacenters while, until now, they were attached to antennas. The main challenge, to fulfill protocol time constraints, is to guarantee a low latency for the periodic messages sent from each antenna to its processing unit and back. The problem we address is to find a sending scheme of these periodic messages without contention nor buffering.We focus on a simple but common star shaped topology, where all contentions are on a single link shared by all antennas. For messages of arbitrary size, we show that there is always a solution as soon as the load of the network is less than 40%. Moreover, we explain how we can restrict our study to message of size 1 without increasing too much the global latency.For message of size 1, we prove that it is always possible to schedule them, when the load is less than 61% using a polynomial time algorithm. Moreover, using a simple random greedy algorithm, we show that almost all instances of a given load admit a solution, explaining why most greedy algorithms work so well in practice.