What is OLT

Recently, Ethernet Passive Optical Networks (EPONs) have received a great amount of interest as a promising cost-effective solution for next-generation high-speed access networks. This is confirmed by the formation of several fora and working groups that contribute to their development, namely the EPON Forum (http://www. ieeecommunities.org/epon), the Ethernet in the First Mile Alliance (http://www.efmalliance.org), and the IEEE 802.3ah working group (http://www.ieee802. org/3/efm), which is responsible for the standardization process. EPONs are a simple, inexpensive, and scalable solution for high-speed residential access capable of delivering voice, high-speed data, and multimedia services to end users (Kramer, Mukherjee, & Maislos, 2003; Kramer & Pesavento, 2002; Lorenz, Rodrigues, & Freire, 2004; McGarry, Maier, & Reisslein, 2004; Pesavento, 2003). An EPON combines the transport of IEEE 802.3 Ethernet frames over a low-cost and broadband point-to-multipoint passive optical fibre infrastructure connecting the optical line terminal (OLT) located at the central office to optical network units (ONUs) usually located at the subscriber premises. In the downstream direction, the EPON behaves as a broadcast and select shared medium, with Ethernet frames transmitted by the OLT reaching every ONU. In the upstream direction, Ethernet frames transmitted by each ONU will only reach the OLT, but an arbitration mechanism is required to avoid collisions. This article provides an overview of EPONs focused several issues: EPON architecture, multipoint control protocol (MPCP), quality of service (QoS), and operations, administration, and maintenance (OAM) capability of EPONs.