说明：   "Ethernet in the First Mile" (EFM) is an upcoming standard currently being drafted by the 802.3ah task force in the IEEE organization. One of the tracks in the standard deals with Ethernet over Passive Optical Network (EPON), a centralized point-to-multi-point network with a shared upstream channel. This paper deals with the problem of upstream bandwidth allocation in EPON networks. We suggest, analyze, and compare several bandwidth allocation algorithms. As a novel type of network, EPON presents many new challenges, and one of the main goals of this project was to get a feel for the network in order to decide on the next steps in its exploration. To that end, we have constructed an OPNET model of an EPON network based on the IEEE