The ALICE experiment, devoted to heavy ion collision studies, is one of the four large detectors of the 27 km Large Hadron Collider (LHC) at CERN. The experiment saw the first circulating beams in September 2008 and is preparing for the first collisions in autumn 2009. The ALICE experiment is composed of 18 sub-detectors, each with up to 15 different sub-systems, such as high voltage, front-end electronics, that need to be controlled with a high level of reliability. The development of a coherent control system for all the various sub-systems and a large variety of devices is a major challenge. In order to assure safe operation of the experiment, each device needs to be configured, controlled, and monitored and all the data involved must be properly refreshed, monitored and stored. The device control is mainly based on OPC, and PVSS SCADA systems customized by CERN. This paper describes the device control architecture, and how it ensures safe and coherent operation using the OPC server / client technology. It also discusses the impact of the communication performance for large-scale control systems dealing with large amounts of data and how this has been optimized.