Achieving Real - Time Communication over
نویسندگان
چکیده
Ethernet continues to be one of the most popular LAN technologies. Due to the low price and robustness resulting from its wide acceptance and deployment, there has been an attempt to build Ethernet-based real-time control networks for manufacturing automation. However, it is diicult to build a real-time control network using the standard UDP or TCP/IP and Ethernet, because the Ethernet MAC protocol, the 1-persistent CSMA/CD protocol, has unpredictable delay characteristics. When both real-time (RT) and non-real-time packets are transported over an ordinary Ethernet LAN, RT packets from a node may experience a large delay due to (i) contention with non-RT packets in the originating node and (ii) collision with RT and non-RT packets from the other nodes. To resolve this problem, we designed, implemented, and evaluated adaptive traac smoothing. Speciically, a traac smoother is installed between the UDP or TCP/IP layer and the Ethernet MAC layer, and works as an interface between them. The traac smoother rst gives RT packets priority over non-RT ones in order to eliminate contention within each local node. Second, it smooths a non-RT stream so as to reduce collision with RT packets from the other nodes. This traac smoothing can dramatically decrease the packet-collision ratio on the network. The traac smoother, installed at each node, regulates the node's outgoing non-RT stream to maintain a certain traac-generation rate. In order to provide a reasonable non-RT throughput, the traac-generation rate is allowed to adapt itself to the underlying network load condition. This traac smoother requires only a minimal change in the OS kernel without any modiication to the current standard of Ethernet MAC protocol or the TCP or UDP/IP stack. We have implemented the traac smoother on both the Linux and the Windows NT platforms, demonstrating signiicant reduction of the RT packet deadline-miss ratio when both RT and non-RT packets are transported over the same Ethernet. More precisely, installation of the proposed traac smoother on every node is shown to reduce the RT message deadline-miss ratio by two orders of magnitude under a heavily-loaded condition, while lowering the non-RT throughput only by half.
منابع مشابه
An Experimental Communication Architecture for Monitoring and Control of Sub-grids
The Smart Grid promises to provide better monitoring and control by incorporating the communication network over the power network. We investigate the monitoring and control of distribution sub-Grids, for example to a local area in a city. We propose a communication architecture to be deployed into a real local area of the sub-Grid to provide a test bed for supporting real-time data and predict...
متن کاملCAN Fieldbus Communication in the CSP–Based CT Library
In closed-loop control systems several realworld entities are simultaneously communicated to through a multitude of spatially distributed sensors and actuators. This intrinsic parallelism and complexity motivates implementing control software in the form of concurrent processes deployed on distributed hardware architectures. A CSP based occam-like architecture seems to be the most convenient fo...
متن کاملScheduling hard and soft real-time communication in a controller area network
The paper introduces a mechanism to implement distributed scheduling for the CAN-bus resource in order to meet the requirements of a dynamic distributed real-time system. The key issues considered here are multicasting, distinguishing between hard real-time, soft real-time, and non-real-time constraints, achieving high resource utilization for the CAN-bus, and supporting dynamic hard real-time ...
متن کاملAchieving Real-time Guarantees in Mobile Ad Hoc Wireless Networks
Timely wireless communication is essential to allow real-time mobile applications, such as communication between mobile robots or inter-vehicle communication to be realized. The real-time event-based communication paradigm has been recognized as an appropriate highlevel communication scheme to connect autonomous components in large distributed control systems [1]. We investigate whether real-ti...
متن کاملAdaptive QoS control for real-time video communication over wireless channels
Robust transmission of real-time video over wireless channels is a challenging problem. This is because the bit error rate (BER) in wireless channels is very high and the bit errors could have devastating effects on the video presentation quality. This paper addresses this problem by introducing adaptive quality-of-service (QoS) control for real-time video communication over wireless channels. ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2000