There is increasing interest in controlling systems over communication networks. Using a simple method called dual-locus diagram, this communique proposes complete stability criteria for a mass-spring-damper system controlled over the network. The stability region is divided into a delay-dependent stability region and a delay-independent stability region, which offers a nice graphical view on the conservativeness of the delay-independent stability criteria. (C) 2003 Elsevier Science Ltd. All rights reserved.