Since NTT East started providing "B FLET'S" Internet connection service using optical fiber in 2001, its speed has continued to increase from the initial 10M/100Mbps, and in 2015 Sony Network Communications Inc. The new plan of "NURO Hikari", which has just started offering, has finally reached 10 Gbps.In 2017, 10 Gbps Internet connection services became available in many areas, including the expansion of areas covered by NURO Hikari 10G.This time, we will explain the "XG-PON" standardized as "G.987" by the ITU, which is the optical fiber standard for 10 Gbps access lines adopted for the NURO Hikari 10G.(Editorial department)As if to follow IEEE 802.3av, the ITU-T will start formulating a successor standard to "G-PON," which was introduced in Part 4, in May 2009.The purpose is not much different from the previous "10G-EPON", the main purpose is to allow individual subscribers to use a wider band, but in addition to this, a little more other uses will come into view.Its use will be described later, but this successor standard to G-PON was initially named "NG-PON (Next-Generation Passive Optical Network)" and later changed to "XG-PON" (where X is Roman numeral 10). The formulation is progressing.In fact, this is a common name, and the official name is "10G-PON", but perhaps to avoid confusion with the preceding 10G-EPON, this name is not used much for some reason.The basic idea is very similar to 10G-EPON for GE-PON, and it was important to realize the following two points.First of all, it was said that it would not be so difficult to achieve 10 Gbps in downlink.This is because G-PON has already achieved 2.5 Gbps, and it is only necessary to quadruple this speed.Moreover, thanks to 10G-EPON, at the time the specifications began to be formulated, it seemed likely that a transceiver (or rather, a laser element on the transmitting side) would be available at a relatively low price.Therefore, the technical difficulty was low.Regarding the second point, mixing with existing G-PON, it was also handled by changing the wavelength used for 10 Gbps and 2.5 Gbps.XG-PON uses wavelengths of 1575 to 1581 nm for downstream and 1260 to 1280 nm for upstream, which does not overlap with G-PON (1480 to 1500 nm for downstream and 1290 to 1330 nm for upstream).Therefore, by inserting a WDM filter on the ONU side and cutting unnecessary wavelengths, both 10 Gbps and 2.5 Gbps can be mixed.However, the difference from 10G-EPON is that the uplink is only 2.5 Gbps.10 Gbps upstream was postponed, and it was said that it would be realized with the next XG-PON2.For this reason, there is no configuration equivalent to the symmetric type that was in 10G-EPON, and there are two choices: G-PON or XG-PON.The figure below is a schematic diagram of a case where G-PON, XG-PON, and video distribution are mixed.The right side is the base station, and the 1550 nm band, which is common to G-PON, GE-PON/10G-EPON, etc., is assigned as OLT for XG-PON and G-PON, and OLT for video distribution.It is a configuration in which WDM is used for this and sent to one fiber.The fiber is then connected to the ONUs in each subscriber's home via a splitter, where the XG-PON (+ video) signal passes through WDM-X (filter for XG-PON), and WDM-G (for G-PON When passed through a filter), G-PON (+ video) signals are obtained respectively.The existing ONU for G-PON cannot be used as it is, and it is necessary to add a WDM-G filter, but since this can be done only by replacing the ONU, it is not a big problem.By the way, the transmission frame itself has been switched to a frame called "XGEM (XG-PON Encapsulation Method)", which is an extension of G-PON's "GEM".Therefore, GTC stores XGEM.By the way, XGEM was changed so that the size of the payload (data storage location) is a multiple of 4 bytes.In addition, "DBA (Dynamic Bandwidth Assignment)" explained in Part 3 is adopted in the same way as GE-PON and G-PON.There are many changes, such as management functions such as "PLOAM (Physical Layer Operation, Administration and Maintenance)" and DBA extension functions such as "DBRu (Dynamic Bandwidth Report)", "bandwidth allocation", and "ranging functions". .One OLT can physically accommodate 64 ONUs (logically 256), with a range of at least 20km and an optional maximum of 60km, which is close to 10G-EPON.In addition, by adopting "FEC" like 10G-EPON to reduce the error rate, it is possible to avoid unnecessary increases in laser output, thereby reducing costs and power consumption.Also, during the standardization work, the OMCI (ONU Management and Control Interface) was expected to be G.987.4, but in October 2010, it was standardized as G.988.As I touched upon at the beginning, XG-PON not only supports FTTH/FTTB (Fiber To The Building)/FTTO (Fiber To The Office) but also "FTTCell" from the beginning.If anything, this is a connection with a mobile phone base station.Conventionally, this was connected as-is with B-PON, G-PON, or GE-PON.However, at that time, C-RAN (Cloud RAN) had not yet been discussed on a large scale, and it seemed that it was just a matter of considering the base station separately.Let's talk about this next time.This time, we explained the optical fiber standard "XG-PON" for 10 Gbps access lines, which was standardized as "G.987" by the ITU.Next time, we will explain the optical fiber standards "XGS-PON" and "NG-PON2" for access lines, which are successors to XG-PON.Freelance technical writer.His expertise spans a wide range of fields, from CPUs, memories, and chipsets to communications, OS, databases, and medical-related fields.Homepage is http://www.yusuke-ohara.com/Uplink 10 Gbps "XGS-PON" standardized as "G.9807.1", followed by 4 x 10 Gbps "NG-PON2" standardized as "G.989"Copyright ©2018 Impress Corporation.