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Statistical Real-Time Communication over Ethernet
March 2003 (vol. 14 no. 3)
pp. 322-335

Abstract—In order to realize real-time communication over Ethernet or fast Ethernet, one must be able to bound the medium access time within an acceptable limit. The multiple access nature of Ethernet makes it impossible to guarantee a deterministic medium access time (hence, packet-delivery deadlines) to individual stations. However, one can bound the medium access time statistically by limiting the packet-arrival rate at the medium access control (MAC) layer. While considering automated manufacturing systems as the main target application, this paper addresses the connection admission control (CAC) problem for statistically bounding the medium access time of Ethernet. Specifically, a packet is guaranteed to have a medium access time smaller than a predefined bound with a certain probability if the instantaneous packet-arrival rate is kept below a certain threshold. Through a mathematical analysis, we first derived such a threshold. In order to keep the packet-arrival rate under the given threshold, we developed and installed a middleware which 1) resides between the transport layer and the Ethernet datalink layer and 2) smooths packet streams between them. The implementation of this middleware requires only a minimal change in the OS kernel without any modification to the current standard of Ethernet MAC protocol or TCP or UDP/IP stack. In order to solve the CAC problem, we derived the probability of transmitting a packet successfully upon each trial by modeling the MAC protocol, 1-persistent CSMA/CD, and the collision resolution protocol—Binary Exponential Backoff—of Ethernet. Our in-depth simulation results have shown this analytic model to provide a reasonably accurate estimate of packet-loss (or deadline-miss) ratio over Fast Ethernet. Finally, we implemented the middleware on the Linux OS, experimentally demonstrating the effectiveness of our approach in providing real-time communication over Ethernet.

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Index Terms:
1-persistent CSMA/CD, (fast) Ethernet, binary exponential backoff, real-time communication, statistical guarantees.
Seok-Kyu Kweon, Kang G. Shin, "Statistical Real-Time Communication over Ethernet," IEEE Transactions on Parallel and Distributed Systems, vol. 14, no. 3, pp. 322-335, March 2003, doi:10.1109/TPDS.2003.1189588
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