We analyze the mean packet delay in an Ethernet passive optical network (EPON) with gated service. For an EPON with a single optical network unit (ONU), we derive (i) a closed form delay expression for reporting at the end of an upstream transmission, and (ii) a Markov chain-based approach requiring the numerical solution of a system of equations for reporting at the beginning of an upstream transmission. Reporting at the beginning, which has not been previously examined in detail, achieves significantly smaller delays than reporting at the end of an upstream transmission for a small number of ONUs. Both of these analyses are fundamentally different from existing polling system analyses in that they consider the dependent switchover times of the EPON. We extend the analysis for reporting at the beginning of an upstream transmission to approximate the mean packet delay in an EPON with multiple ONUs and verify the accuracy of the analysis with simulations. Overall, our numerical results indicate that for utilizations up to ~75%, the mean packet delay is close to its minimum of four times the one-way propagation delay.
© 2008 Optical Society of AmericaPDF Article