Achieving real-time communication over Ethernet with adaptive traffic smoothing

Abstract

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 di cult to build a realtime 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 c haracteristics. 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 p a c kets from the other nodes. To resolve this problem, we designed, implemented, and evaluated adaptive tra c smoothing. Speci cally, a tra c smoother is installed between the UDP or TCP/IP layer and the Ethernet MAC l a yer, and works as an interface between them. The tra c smoother rst gives RT p a c kets priority o ver 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 tra c smoothing can dramatically decrease the packet-collision ratio on the network. The tra c smoother, installed at each node, regulates the node's outgoing non-RT stream to maintain a certain tra c-generation rate. In order to provide a reasonable non-RT throughput, the tra c-generation rate is allowed to adapt itself to the underlying network load condition. This tra c smoother requires only a minimal change in the OS kernel without any modi cation to the current standard of Ethernet MAC protocol or the TCP or UDP/IP stack.We h a ve implemented the tra c smoother on both the Linux and the Windows NT platforms, demonstrating signi cant reduction of the RT p a c ket deadline-miss ratio when both RT and non-RT packets are transported over the same Ethernet. More precisely, installation of the proposed tra c smoother on every node is shown to reduce the RT message deadline-miss ratio by t wo orders of magnitude under a heavily-loaded condition, while lowering the non-RT throughput only by h a l f .

Full Duplex Switched Ethernet for Next Generation "1553B"-Based Applications

“…Traffic Shaping approach has been initiated by Kweon and Shin [15] Ethernet. The idea is that a smooth traffic, in which messages arrive at a constant rate, suffers less from collisions than a bursty traffic.…”

Modular software architecture for flexible reservation mechanisms on heterogeneous resources

“…Some of them have been realized in industrial standards, such as DDS [36], Ethernet Powerlink [16,47], or Profinet IO [40]. The suggested methods usually propose traffic smoothing [30,3] or time-triggered approaches [38,28].…”

Survey of Real-Time Communication in CSMA-Based Networks

“…Finally, the traffic smoothing mechanisms proposed by Kweon et al [12,44] constrain the packet generation rate of non-RT messages below a defined threshold, in order to provide a probabilistic guarantee of message delivery. The original traffic smoothing proposal uses the well-known leaky bucket regulator [45].…”

“…The HIMD (Harmonic-Increase and Multiplicative Decrease) [44] is a dynamic policy that uses the credit bucket depth and the refresh period as a dynamic traffic regulator; in the absence of collisions, it periodically increases the input bound by periodically reducing the refresh period. In [13], the smoothing actions are performed by a fuzzy controller, where the network load is observed along determined time intervals, via the measurement of the throughput and of the number of occurring collisions.…”