Performance Evaluation of Control Networks: Ethernet, ControlNet, and DeviceNet

1 Introduction The traditional communication architecture for control systems is point-to-point, which has been successfully implemented in industry for decades. However, expanding physical setups and functionality push the limits of the point-to-point architecture. Hence, a traditional centralized point-to-point control system is no longer suitable to meet new requirements , such as modularity, decentralization of control, integrated diagnostics, quick and easy maintenance, and low cost 1]. Network systems with common-bus architectures, called Networked Control Systems (NCSs), provide several advantages such as small volume of wiring and distributed processing. Especially with respect to manufacturing systems, NCS architectures that utilize processing power at each node allow for modularization of func-tionality and standard interfaces for interchangeability and interoperability. Object-based device models separate generic, device-type speciic from manufacturer-speciic functionality. Many diierent n e t work types have been promoted for use in control systems. In this article, we compare three of them: Ethernet bus (CSMA/CD), Token passing bus (e.g., ControlNet) and Controller Area Network (CAN) bus (e.g., DeviceNet). Distributed systems contain a large number of devices interconnected together to perform the desired operations over a large area of coveragee examples include industrial automation, building automation, ooce and home automation, intelligent v ehicle systems, and advanced aircraft and spacecraft 2-6]. Data networks or control networks may be used, depending on the information exchanged. Data networks are characterized by large data packets, relatively infrequent bursty transmission, and high data ratess they generally do not have hard real-time constraints. Control networks, in contrast, must shuttle countless small but frequent packets among a relatively large set of nodes to meet the time-critical requirements. The key element that distinguishes control networks from data networks is the capability to support real-time or time-critical applications 7]. With NCSs, decisions and control functions (including signal processing) can be distributed among controllers on the network. However, when designing a NCS, a new constraint must be accommodated | the limited bandwidth of the communication network. The eeective bandwidth of a network is deened as the maximum amount of meaningful data that can betransmitted perunit time, exclusive of headers, padding, stuung, etc. and the network bandwidth is equal to the numberof raw bits transmitted per unit time. Four factors aaect the availability and utilization of the network bandwidth: the sampling rates at which the various devices send information over the network, the numberof elements that require synchronous operation, the data or message size of the information, …