Passive optical network (PON) is the use of point-to-multipoint tree fiber distribution network for information transmission technology. Point-to-multipoint physical topology is particularly useful for wired access networks. The PON system is typically composed of an OLT device located at the central office, PON an ONU device located on the user side, and a passive optical distribution network connecting the two.
PON system because multiple ONU devices share the same optical media and OLT communication, so the main need to address the different ONU media sharing between the problem. The main ways to solve media sharing in fiber include time division multiplexing / multiple access technology, PON wavelength division multiplexing and orthogonal frequency division multiplexing (OFDM) technology. So the main PON technology can be divided into TDM-PON, WDM-PON and OFDM-PON three categories. At present, the technology is more mature and widely used EPON, GPON and so on are mainly used TDM-PON technology.
The earliest PON system is mainly used to solve the multiple narrowband access network (digital subscriber loop) remote device interconnection, transmission n × 64 kbit / s voice slot. PON But because of the price and business protection can not be with the ring topology of the digital user loop equipment to compete, so a failed technology
In the 1990s, with the rise of ATM / B-ISDN, broadband became the important direction for the development of telecommunication technology for the first time, and the fiber technology with great potential for bandwidth became the darling of information transmission technology. Therefore, PON in 1995, seven major operators around the world set up a full service access network organization (FSAN), PON is committed to the optical fiber access network standards and application of the promotion work. With the joint efforts of FSAN and ITU-T, the first international standard for PON systems "Broadband Optical Access System Based on Passive Optical Network (PON)" (ITU-T G.983.1) was released in 1998, which Standards are also commonly referred to as BPON standards.
BPON in the current technical environment using the ATM as the core of the design ideas, and limited to the device level and price factors, PON equipment, the cost is still relatively high, PON fiber access network external supporting conditions are not mature, so BPON only In the North American telecom operators have a certain size of the deployment, not in the world to obtain a wide range of applications.
With the decline of ATM technology and the rapid rise of Internet IP technology, following BPON, the industry hopes to develop a new PON system, replacing the outdated BPON technology. In this context, IEEE and ITU-T have started EPON and GPON standardization work in 2000 and 2001, respectively, PON and issued the completed standards in 2004, laying the foundation for today's EPON and GPON applications in the current network The foundation.
The EPON standard was completed by the IEEE EFM (Ethernet in the First Mile) working group and was approved by the IEEE as IEEE 802.3ah standard in September 2004. PON Many of the contents of the EPON standard inherited the design of Ethernet, reused the Gigabit Ethernet and physical layer coding and other content, PON and MAC layer protocol and Ethernet frame preamble sequence was modified to meet the PON point to Multi-point network topology.