PON (Passive Optical Network: Passive Optical Network). PON (passive optical network) refers to the (light) in distribution network does not contain any electronic devices and electronic power, ODN all by optical divider (Splitter) passive components such as composition, does not require expensive active electronic devices. A passive optical network includes a light line terminal (OLT) installed in a central control station, as well as a set of complementary optical network units (ONUs) that are installed in the user site. The optical distribution network (ODN) between OLT and ONU contains optical fiber and a passive splitter or coupler.
PON system structure is mainly composed of center office of the Optical Line Terminal (OLT: Optical Line Terminal), including passive Optical components of Optical Distribution Network (ODN: Optical Distribution Network, Optical Network Unit of client/Optical Network Terminal (ONU/ONT Optical Network Unit/Optical Network Terminal), the difference is ONT the client directly, but the ONU and between users and other networks, such as Ethernet) and the composition of Network element management system (EMS), usually adopt point to multipoint tree topology structure.
The outstanding advantage of PON network is to eliminate the outdoor active equipment, all the signal processing functions are completed in the switch and the user's house device. And the upfront investment is small, and most of the money will be deferred until the user actually has access to it. Its transmission distance is shorter than that of active optical fiber access system, and the coverage is smaller, but it is low cost, and it is not required to set up the machine room and maintain easy maintenance. So this structure can be economically used for home users.
PON's complexity is signal processing technology. In the downward direction, the switch signals the broadcast to all users. In the upward direction, each ONU must adopt some Multiple Access protocol such as TDMA (Time Division Multiple Access) protocol to complete the Shared transmission channel information Access. The current PON technology for broadband access includes EPON and GPON.
PON technology status quo
The traditional data stream of the PON system adopts TDMA technology using broadcast technology and uplink data flow, so as to solve the multiplexing problem of each direction signal. Traditional PON technology adopts WDM technology to realize single-fiber two-way transmission on optical fiber and solve the multiplexing transmission of two directional signals. PON is generally composed of optical line terminal (OLT), spectrometer (ODU) and user terminal (ONU). Currently, the widely used PON technology in the current network includes EPON and GPON 2 mainstream technologies, EPON and upstream bandwidth are 1.25 Gbit/s, GPON's lower bandwidth is 2.5 Gbit/s, and the upward bandwidth is 1.25 Gbit/s.
Currently, in the actual FTTx application scenario, most EPON/GPON only have an Ethernet interface, optional configuration POTS and 2M interfaces. However, from the technical standards, EPON/GPON can realize multiple business access such as IP business and TDM business, and can realize the QoS classification.
The EPON/GPON can transmit the clock synchronization signal, and can extract the frequency synchronization signal from the external circuit through the stm-1 interface or GE interface of OLT, and the OLT needs to support synchronous Ethernet. It is also possible to input the clock signal from external BITS on the OLT device as the public clock source of the PON, and the ONU is in sync with the clock source.
Relatively low cost
1) relatively low cost, easy to maintain, easy to expand and easy to upgrade. The PON structure is not required for power supply during transmission, it has no electronic parts, so it is easy to lay, without maintenance, and the long-term operation cost and management cost are very large
Pure media network
2) the passive optical network is a pure media network, which completely avoids the electromagnetic interference and lightning effect, and is suitable for use in areas with poor natural conditions.
3) the PON system has a very small amount of innings, and the system has low initial input, easy expansion and high return on investment
4) provide very high bandwidth. EPON can now provide a symmetric 1.25Gb/s bandwidth and can be upgraded to 10Gb/s with the development of etheric technology. GPON is up to 2.5 Gb/s.
5) scope of service. PON, as a point-to-point network, USES a fan-shaped structure to save CO's resources and serve a large number of users. User investment is saved by sharing the device and the optical fiber.
6) the bandwidth allocation is flexible and the service quality (QoS) is guaranteed. The G/EPON system has a complete system for bandwidth allocation and guarantee. User level slas can be implemented.