On the Behavior of Ethernet: Are Existing Analytic Models Adequate?

In this report, we have developed a detailed Ethernet simulation model whose accuracy has been validated against published measurement data from real Ethernet configurations. Our simulator has the additional capability of embedding the Ethernet subsystem in some simple closed queueing networks that can be modeled easily using Mean Value Analysis (MVA) techniques. Our motivation here is to assess the sensitivity of high-level MVA models of Ethernet-based distributed systems to the approximations made in existing analytical models, in particular the Flow Equivalent Service Center of Almes and Lazowska. After studying the operating characteristics of the protocol in a number of open and closed systems, we have concluded that the existing CSMA/CD analytic models do not capture the behavior of the Ethernet protocol except under light loads. The discrepancies are due mainly to the operation of the binary exponential backoff algorithm, which becomes a predominant factor under high loads. Howe..