GPON 0AM USING IEEE 802.1 ag METHODOLOGY BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates generally to passive optical networks (PONs) and, more specifically, to QAM features in PON technology. Description of the Related Art [0002] GAM, which stands for "operations, administration and management," is a term commonly used to describe the instrumentation of telecommunications networks with tools to allow network operators to remotely install, monitor and troubleshoot elements of their networks. Early network management methodologies generally involved the exchange of messages directly between a central network management platform (e.g., a network server) and each of the other network nodes, so that each node could be monitored and controlled from the central network management system. With Ethernet developing into the dominant network technology for delivering broadband services, such as Internet access, digital telephony and television, a need became apparent for a methodology to aid network service providers in verifying end-to-end connectivity of Ethernet-based network service to their subscribers. Such a methodology has been referred to in the art as Connectivity Fault Management (CFM). Accordingly, an Ethernet OAM standard for CFM, known as IEEE 802.1 ag, has been developed. End-to-end CFM refers to the ability of a network to monitor the "health" of a service delivered to end-users, as opposed to just links or individual bridges. Ethernet OAM has been used in networks that deliver services to subscribers via digital subscriber lines (DSL) and similar wire-based broadband connections. [0003] The IEEE 802.lag standard defines a "Maintenance Entity" domain hierarchy, with a customer-level domain at the highest level of the hierarchy, and one or more provider domains at intermediate levels, each of which in turn includes one or more operator domains disposed at a lower hierarchical level. A Maintenance Entity domain level is defined in terms of what are referred to as flow points. In the context of the IEEE 802.lag specification, the flow points are (typically, software) entities that operate in the Media Access Control (MAC) "interfaces" and "ports" of switches, routers and other Ethernet devices. A port can implement multiple flow points of different types. A flow point at the edge of an 0AM domain is called a "Maintenance End Point" or MEP. MEPs can, among other functions, initiate test messages. A flow point inside an 0AM domain and visible to an MEP is called a "Maintenance Intermediate Point" or MIP. Whereas MEPs initiate test messages, either on an automatic basis or at the request of system administrators, MIPs passively receive and respond to 0AM flows initiated by MEPs. The messages initiated by MEPs on a Maintenance Entity level are generally confined to that level and invisible to MEPs and MIPs on other levels. [0004] Most Ethernet-based service provider networl