ODN (Optical Distribution Network)
ODN is a FTTH fiber optic cable network based on PON equipment. Its role is to provide optical transmission channel between the OLT and ONU. Accroding the function, ODN from the central office to the client can be divided into four parts: feeder fiber optic subsystems, cable wiring subsystem, home line of fiber optic subsystems and fiber terminal subsystems. The main components in ODN include optical fibers, optical connectors, optical splitters and corresponding equipments for installing them.
OLT (Optical line terminal)
OLT is a terminal equipment connected to the fiber backbone. It sends Ethernet data to the ONU, initiates and controls the ranging process, and records the ranging information. OLT allocates bandwidth to the ONU and controls the starting time and the transmission window size of the ONU transmission data.
ONU (Optical network unit)
ONU is a generic term denoting a device that terminates any one of the endpoints of a fiber to the premises network, implements a passive optical network (PON) protocol, and adapts PON PDUs to subscriber service interfaces. In some contexts, ONU implies a multiple subscriber device. Optical Network Terminal (ONT) is a special case of ONU that serves a single subscriber.
APON / BPON
APON (ATM PON) is the first PON system that achieved significant commercial deployment with an electrical layer built on Asynchronous Transfer Mode (ATM). BPON (Broadband PON) is the enhanced subsequence of APON, with the transmission speed up to 622Mb/s. At the same time, it added the dynamic bandwidth distribution, protection and other functions. APON/BPON systems typically have downstream capacity of 155 Mbps or 622 Mbps, with the latter now the most common.
GPON (Gigabit PON) is based on the TU-TG.984.x standard for the new generations of broadband passive optical access. Compared with the other PON standards, GPON provides the unprecedented high bandwidth downlink rate of up to 2.5 Gbit/s, the asymmetric features better adapt to the broadband data services market. It provides the QoS full business protection, at the same time carries ATM cells and (or) GEM frame, the good service level, the ability to support QoS assurance and service access. Carrying GEM frame, TDM traffic can be mapped to the GEM frame, 8kHz using a standard frame able to support TDM services. As a carrier-grade technology standards, GPON also provides access network level protection mechanism and full OAM functions. GPON is widely deployed in FTTH networks. It can develop into two directions which is 10 GPON and WDM-PON.
WDM-PON uses wavelength division multiplexing technology to access to the passive optical network. It has four programs as following:
1. Each ONU is assigned with a pair of wavelength, for uplink and downlink transmission, thereby providing the OLT to each ONU fixed virtual point-to-point bidirectional connections.
2. ONU uses tunable lasers, according to the needs of the ONU to dynamically allocate the wavelength, and each ONU can be shared the wavelength, the network are reconfigurable.
3. Using colorless ONUs, the ONU are independent from the wavelength.
4. Using a combination of TDM and WDM technology, Composite PON (CPON). CPON uses WDM technology in the downstream, and TDMA technology in the upstream.
EPON / GEPON
EPON (Ethernet PON) is the rival activity to GPON which uses Ethernet packets instead of ATM cells. GEPON uses 1 gigabit per second upstream and downstream rates. It is a fast Ethernet over PONs which are point to multipoint to the premises (FTTP) or FTTH architecture in which single optical fiber is used to serve multiple premises or users. EPON is an emerging broadband access technology, through a single fiber-optic access system, to access the data, voice and video service, and it has a good economy.