STATUS OF GPON AND B-PON STANDARDS

摘要

Passive Optical Networks (PONs) have been the subject of much research and development over the past 10 years or so. This technology is seen as an effective solution to the broadband access problem encountered so often today. With the recent uptake of services such as Internet data access and advanced video services, the current access networks based on copper or coaxial cables are beginning to become overburdened. Thus, the interest in PONs has increased significantly. There are many types of PONs, but the most popular designs are based on a tree-and-branch fiber network that provides connectivity between a single central station and a plurality of end stations, as shown in Figure 1. The transmissions on this network are controlled via time division multiplexing on the downstream link, and time division multiple-access on the upstream link. For this type of PON, there has been a consistent standardization effort within the International Telecommunications Union (ITU). The primary goal of this effort is to promote the development and deployment of equipment that is consistent with internationally agreed-upon standards. The work on the current generation of PON equipment began in 1996, with the study of an ATM based PON system. This system has been recently enhanced and expanded, and is now commonly referred to as Broadband PON, or B-PON for short. This was the follow-on from a previous effort on a Synchronous Transfer mode (STM) based PON, which was described in ITU-T standard G.982. The older system was based on transmission speeds of less than 100 Mb/s, and was quickly made obsolete by the advance of both optics and electronics. The B-PON system operates in speeds between 155 Mb/s and 1244 Mb/s. It will be described in Section 2. Recognizing that technology and service demands have grown and changed over the past 7 years, the ITU has engaged on a new PON system, whose intent is to cover speeds beyond 1 Gb/s. This effort has been named Gigabit PON, or GPON for short. This effort is currently in process, and will soon be coming to a conclusion. This new system will be described in some technical detail in Section 3. It is well known that standardization by itself makes little progress. Therefore, industry consortia, like the Full Services Access Network (FSAN) group, have promoted the development of components, systems, and deployment specifications that work together. The membership in these groups has recently expanded, and there are now multiple vendors for such items as optical transceivers, B-PON media access control chips, optical network units (ONUs), and Optical line terminals (OLTs). The result of these efforts will briefly be reviewed in Section 4.