Optical networks, relying on optical fiber and other optical hardware, make up the networks that are the nerves of the internet. Outside of a home or office, the electrical cables typically connect to optical cables, which provide the interconnect among data centers and optical line terminals (OLT) at user locations. There are a variety of optical fiber network technologies, including several passive optical networks (PONs).
By definition, passive networks don’t involve any active hardware. This means that only passive hardware is used to carry, combine, split, filter, or otherwise condition the signals traveling in the network signal path. Hence, with a PON the optical distribution network (ODN) is only composed of passive components, which are generally less expensive than active optical components. A PON has an OLT at the central control station and one or more associated optical network units (ONUs) located at customer premises. In between these two locations within a PON, are passive components splitting, combining, and conditioning the signal.
As mentioned earlier, there are several types of PONs. Namely, there are Ethernet passive optical networks (EPONs), gigabit passive optical networks (GPONs), and more recently 10G passive optical networks (10G-PONs). EPONs are a competitive technology to GPON, which uses ethernet packets as opposed to asynchronous transfer mode (ATM) cells established by ANSI and the ITU. With EPON, a 1 gigabit per second upstream and downstream transfer rate can be achieved that also allows for point-to-multipoint architecture that can use a single optical fiber to serve multiple premises. EPON is an emerging broadband access technology for access to data, voice, and video services and can be part of a fiber-to-the-home (FTTH) or fiber-to-the-premises (FTTP) PON.
GPON, on the other hand, is based on TU-TG.984X standards for broadband passive optical access and offers downlink rates to 2.5 Gbps. GPON is asymmetric, unlike EPON, but is designed for a high quality-of-service for business use cases (QoS assurance and service access). GPON also uses an access level protection mechanism (ALPM) and full operations, administration, and management (OAM) functions. A recent variation of GPOM is 10G-PON, which is an extension of GPON that offers 10 Gbit/s usable bandwidth, established in 2010 (also known as XG-PON). Both GPON and 10G-PON can serve up to 128 ONUs, where 10G-PON can service 128 users per PON and possibly more with active reach extenders/amplifiers.
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