Characterizing the Real-Time Behavior of Prioritized Switched-Ethernet 1

Ethernet is, today, the de facto standard in the Local Area Networks general domain. Despite having been designed for the office environment, it has been appropriately modified or adapted in order to fulfill the requirements of many other fields, including large distributed embedded systems and industrial automation. One typical requirement in such application fields is the need to deliver time-constrained communication services, which cannot be efficiently met using the original CSMA/CD medium access control. Among many possible solutions, either software or hardware-based, the one that became more popular, recently, is the use of switches. However, this does not enforce timeliness per se. In this paper we show a set of practical experiments that reveal the weaknesses of switched Ethernet in what concerns real-time behavior. The results point to the need for further traffic control, at the data sources, if a predictable behavior of the switch is desired.