Development and prospect of PON

What is pon

PON is a typical passive optical fiber network, which means that the optical distribution network does not contain any electronic devices and electronic power supplies, ODN is all composed of passive devices such as optical splitters and does not require expensive active electronic equipment. A passive optical network includes an optical line terminal (OLT) installed in the central control station, and a number of matching optical network units (ONUs) installed in the user’s premises. The industry has always believed that the passive optical network (PON) is the future development direction of the access network. On the one hand, because the bandwidth it provides can meet the needs of various broadband services now and in the future, it is generally optimistic about solving the problem of broadband access; On the other hand, its expenses are both in terms of equipment cost and operation and maintenance management overhead. Both are relatively low. Comprehensive economic and technical analysis shows that PON is the main technology for FTTB/FTTH.

The development of the PON

PON(Passive Optical Network) is a point-to-multipoint passive optical access technology, which originated in the 1990s.From the development of narrowband PON to various broadband PON technologies,the development of PON technology has gone through several stages.

Narrowband PON technology is the earliest proposed PON technology, which can only provide narrowband services such as POTS or ISDN with service access rates below 2Mbit/s. However, due to the inconsistent specifications of various manufacturers and the inability to reach agreement at that time, there is still no unified and complete standard for narrowband PON technology. In the era of continuous development of the Internet, narrowband PON has long withdrawn from the stage of history, and then APON technology appeared in the mid-1990s. APON used the ATM protocol, which was considered to be able to provide various types of communications at that time, as the bearer protocol, and the transmission rate has been greatly improved. Later, with the rapid development of Ethernet technology, APON is basically no longer applicable, so the concept of broadband passive optical network BPON appeared. BPON is an enhancement after the APON standard, and is also based on the ATM protocol, and the uplink and downlink rates have been greatly improved. ITU-TG.983.1, the first international standard for PON systems released in 1998, is also generally referred to as the BPON standard.

Since entering the 21st century, with the decline of ATM technology and the rapid rise of Internet IP technology, the high-cost deployment of BPON technology seems a bit outdated. At this time, the industry hopes to develop a new PON system to replace the outdated BPON technology. In this context, IEEE and ITU-T successively initiated the standardization of EPON and GPON in 2000 and 2001, and respectively issued the completed standards in 2004, laying the foundation for the large number of applications of EPON and GPON in the current network today. The EPON standard was completed by IEEE’s EFM (Ethernet in the First Mile) working group, and was approved by the IEEE as the IEEE 802.3ah standard in September 2004. The GPON standard is standardized by ITU-T Study Group 15. The GPON-related standards include G.984.1-G.984.6 six standards, covering the GPON system architecture, physical media related layers, transmission convergence layer, ONU control management Protocols and regulations for enhanced wavelength usage and distance extension. Compared with the BPON system, the upstream and downstream rates of EPON and GPON have been greatly improved. The upstream and downstream bandwidth of EPON is 1.25 Gbit/s, while the downstream bandwidth of GPON is 2.5 Gbit/s and the upstream bandwidth is 1.25 Gbit/s.

With the rapid development of IP business volume and the continuous increase in the number of users, 10GEPON and XG-PON supporting higher split ratio and higher bandwidth have also emerged. Beginning in 2005, IEEE and ITU have successively carried out standardization studies on the next-generation PON system. IEEE established a project in 2006 and began to formulate the standard IEEE 802.3av for EPON systems with a rate of 10 Gbit/s. In this standard, 10G EPON is divided into 2 types. One is the asymmetric method, that is, the downstream rate is 10 Gbit/s, but the upstream rate is the same as EPON and is still 1 Gbit/s. The second is the symmetrical approach, that is, the uplink and downlink rates are both 10 Gbit/s. As the first mature next-generation PON technology, 10GEPON technology is in line with network development trends. It has the advantages of large bandwidth, large optical splitting ratio, compatibility with EPON, unified network management, and smooth upgrade. ITU started the study of the next-generation GPON standard in 2008 and confirmed it in 2010. It is currently called the XG-PON standard. The XG-PON standard ITU-T G.987 series have been released one after another. The physical layer rate currently specified by XG-PON is asymmetric, that is, the downstream rate is 10 Gbit/s and the upstream rate is 2.5 Gbit/s. In 2015, the XGPON symmetrical solution that was cancelled in 2013 was restarted again and adopted the new name XGSPON. Unlike XGPON, the XGSPON upstream and downstream rates are both 10Gbit/s, and the ITU officially passed G.9807 in 2017. XGSPON international standard. In recent years, Internet applications such as video and games have developed rapidly, and users have a strong demand for network broadband, which has further stimulated the maturity of the 10GPON industry chain. Commercial deployment of 10G PON has begun in some cities in China.

After the establishment of the XGPON standard, FSAN started the study of NG-PON2. Its key requirements are mainly 40G downlink and 40G/10G uplink, achieving 20km transmission distance and 1:64 splitting. At that time, mainstream alternative technical solutions for NG-PON2 included high-speed TDMA-PON, TWDM PON, OFDM-PON and WDM-PON. After analysis and comparison, in April 2012, FSAN decided to adopt TWDM PON technology as the implementation plan of NG-PON2, and started to formulate the G.989.x series of standards, which was finally completed in 2015. The IEEE started NG-EPON research in 2013, and started the formulation of the 100G-EPON standard in July 2015, named IEEE802.3ca, and plans to release it within this year.

optical network unit

The future of the PON

It is not difficult to imagine that in the future, we need a PON technology with larger bandwidth, more users and higher efficiency. 25G/50G/100GPON has already been put on the agenda of the standards organization. In February 2018, China’s optical access network industry successfully promoted the establishment of the 50G TDM-PON standard, marking a key step taken by ITU-T in the field of next-generation PON standard research. Although IEEE did not accept the establishment of a single-wave 50G PON project, it at least clarified the future technological evolution route of PON. For the future 100G PON technology, China’s communication equipment vendors are actively investigating 100G PON technology to jointly promote standard formulation and maturity of the industry chain. The application of 100G PON is only a matter of time.

With the development of the times and the continuous advancement of science and technology, 200G/5OOG/1000G and even higher PON technologies will be slowly realized. However, in addition to studying the next generation of PON technologies, the industry is still paying close attention to a very important issue. That is, the convergence of the two technical schools of ITU-T and IEEE. EPON and GPON coexist for a long time, which is actually very unfavorable to the industry. On the one hand, it brings difficulties to the technical decisions of operators and equipment; on the other hand, it also increases the cost of the industrial chain, and industrial chain enterprises need to invest in two lines. Especially for the huge optical access network market like China, the influence of the differentiation of PON technology factions is even greater, and more waste of resources. In recent years, under the active promotion of domestic and foreign industries, ITU-T and IEEE have also made some positive “shows”, including issuing joint statements, forming working groups, and establishing liaison letter mechanisms. But for now, it will take a long time to truly realize the final integration.