GPON

G.984 is the ITU-T standard for implementing a gigabit-capable passive optical network (GPON). It is commonly used to implement the outermost link to the customer (last kilometre or last mile) of fibre-to-the-premises (FTTP) services. GPON puts requirements on the optical medium and the hardware used to access it, and defines the manner in which Ethernet frames are converted to an optical signal, as well as the parameters of that signal. The bandwidth of the single connection between the OLT (optical line termination) and the ONTs (optical network terminals) is 2.4 Gbit/s down, 1.2 Gbit/s up, or rarely symmetric 2.4 Gbit/s, shared between up to 128 ONTs using a time-division multiple access (TDMA) protocol, which the standard defines. GPON specifies protocols for error correction (Reed–Solomon) and encryption (AES), and defines a protocol for line control (OMCI) which includes authentication (LOID, serial number and/or password). Though implementations of GPON share a lot of common features, many features were left undefined, thus in practice, there is little compatibility between the various implementations. Specifically, the exact kind of fibre cable and connectors to use is undefined. The primary optical transmitter, known as the Optical Line Terminal (OLT), is housed within the central office of the telecommunications operator. A laser in the OLT injects photons from the central office into a glass-and-plastic fiber-optic cable that terminates at a passive optical splitter. The splitter divides the single signal from the central office into many signals that can be sent to up to 64 consumers. The number of consumers serviced by a single laser is determined by the operator's engineering criteria; operators may opt to reduce the number to 32 consumers. Furthermore, the operator may choose to divide the signal twice, for example, once into eight and again farther down the line. The maximum distance between the central office and the site can be 20 kilometers, however operators will normally limit it to 16 kilometers in order to maintain a high level of service.