Industrial use requires consideration of the environment in which the equipment must operate. Factory equipment must tolerate a wider range of temperature, vibration, physical contamination and electrical noise than equipment installed in dedicated information-technology wiring closets. Since critical process control may rely on an Ethernet link, economic cost of interruptions may be high and high availability is therefore an essential criterion. Industrial Ethernet networks must interoperate with both current and legacy systems, and must provide predictable performance and maintainability. In addition to physical compatibility and low-level transport protocols, a practical industrial Ethernet system must also provide interoperability of higher levels of the OSI model. An industrial network must provide security both from intrusions from outside the plant, and from inadvertent or unauthorized use within the plant.