Since NTT East started providing the Internet connection service "B FLET'S" using optical fiber in 2001, the speed has continued to increase from the initial 10M / 100Mbps, and in 2015 Sony Network Communications Co., Ltd. With the new plan of "NURO Hikari" that we have started to provide, we have finally reached 10 Gbps.In 2017, the target area of ​​"NURO Hikari 10G" expanded, and 10Gbps Internet connection service became available in many areas.This time, the optical fiber standard "XGS-PON" and "G. I will explain about "NG-PON2" standardized as "989.3".(Editorial department)The drawback of the "XG-PON" introduced last time is that the uplink (ONU → OLT) was 2.5 Gbps.However, it was probably a marketing or cost issue rather than focusing on 2.5 Gbps due to technical restrictions, and it was not so difficult to speed up the uplink to 10 Gbps technically.Perhaps because of that, ITU-T will start standardizing the next "XGS-PON" after the standardization of XG-PON is completed.To tell the truth, this was a plan from the beginning.Initially, the specification of XG-PON was started under the name of "NG-PON (Next-Generation PON)", but at this stage, the upstream 2.5 Gbps version that maintains compatibility with G-PON and the upstream version It was a stipulated route to prepare two versions of the speed increased to 10 Gbps.After that, they were also called XG-PON1 and XG-PON2, respectively, but in the end, the latter 10Gbps uplink was named "XGS-PON".XGS means "10 (X) G Symmetric" (10G symmetric type), which means that both uplink and downlink have reached 10 Gbps.The specifications of XGS-PON are a little interesting.In ITU-T, the standardization of XGS-PON has started after XG-PON, but at the same time, the standardization of NG-PON2, which will be explained next time, has also started. I feel that the work has progressed with one hand of NG-PON.The physical standard of XGS-PON, that is, the transceiver, is the same as that of XG-PON and 10GE-PON.The wavelengths used are 1575 to 1581 nm for downlink and 1260 to 1280 nm for uplink, which are almost the same as XG-PON.On the other hand, regarding the protocol layer, in addition to XG-PON, some specifications of "NG-PON2" standardized as ITU "G.989.3" are incorporated.However, regarding the management function of ONU, the "OMCI (ONU Management and Control Interface)" of "G.988" that appeared in XG-PON is used as it is.By the way, like XG-PON, XGS-PON has different specifications for PMD layer and TC layer, and "G.989.2" and "G.989.3" established for NG-PON2 are used as they are. It is supposed to be.Rather, it should be said that the specifications of NG-PON2 include the specifications of XGS-PON.The specifications of XGS-PON were established in 2016, and the release of Amendam 1 was in October 2017. Since the specifications are close to "just completed", there are no cases of adoption in Japan so far. It seems that they are considering the introduction of NG-PON2 or later (especially NG-PON2 +) explained in.This is not just about "FTTH (Fiber To The Home)", but about 5G.I will explain the details of this area next time.However, looking overseas, the three carriers in China have introduced XG-PON from the beginning on the premise of upgrading to XGS-PON.Depending on the spread of 5G in the future, XGS-PON may be introduced for 5G infrastructure in developing countries as well as developed countries.In fact, even with 100G Ethernet, which was first standardized as "IEEE 802.3ba" in 2007, 100Gbps could not be achieved with a single optical fiber, and the approach of bundling four 10Gbps to 40Gbps and bundling 10 to 100Gbps. was.After that, "IEEE 802.3bm" was finally standardized in 2014, but even so, with a 25Gbps x 4 configuration, the speed has finally been increased to about 50Gbps.As mentioned above, the standardization work for NG-PON2 started immediately after the specification of XG-PON was completed, so the technology at that time had an upper limit of about 10 Gbps.Of course, there were elements that were a little faster if the price was ignored, but if it was "FTT Cell" for mobile phone base stations, which is acceptable depending on the conditions even if it is a little expensive, and "FTTB (Fiber To The Building)" for collective use. In any case, low prices are essential for FTTH for homes and "FTTO (Fiber-To-The-Office)" for corporations, so the signal speed itself is virtually limited to 10 Gbps.Therefore, "WDM (Wavelength Division Multiplexing)" was adopted in NG-PON.In Japanese, it is translated as a wavelength division multiplexing method, but in short, it can be said to be an extension of the method used by PON to pass light of multiple wavelengths through a single fiber.By this definition, all PON so far can be said to be WDM.However, WDM in a narrower sense is adopted in NG-PON2.The figure below is an excerpt from the material of G.989.2 and shows the wavelengths used.In NG-PON, the part (1525nm to 1625nm) written as "PtP WDM EXPANDED SPECTRUM" in the lower right is newly used.Of these, the light orange "TWDM U / S" is used for the uphill of NG-PON2 (ONU → OLT), and the dark orange "TWMD D / S" is used for the downhill of NG-PON (OTL → ONU). Become.Until now, for example, the wavelengths of GPON's upstream (1290 to 1330 nm) and XG-PON's upstream (1260-1280 nm) differed significantly, but with NG-PON2, there are multiple wavelength bands of 40 nm upstream and 20 nm downstream. It is designed to allow light to pass through.In the case of NG-PON2, light of 4 wavelengths (8 wavelengths as an option) is passed through this range, and each is transferred at a maximum of 10 Gbps, so that a total bandwidth of 40 Gbps can be used.Then, if the ONU side can use a maximum of 40 Gbps, it will be a maximum of 10 Gbps.The following is an excerpt from NTT's technical journal, but from the OLT side, each of the four wavelengths is sent out at a maximum of 10 Gbps (TWDM λ1 to λ4), and this is sent out to one fiber using a mixer.However, the TWDM ONU on the receiving side can receive only one wavelength from λ1 to λ4, so the maximum is 10 Gbps.Of course, it is technically possible to receive all four wavelengths, but it is expensive, so it was postponed in this generation.By the way, although the maximum is 10 Gbps, the actual transfer rate is either 2.5 Gbps or 10 Gbps, and the ONU side can dynamically change the wavelength received.In actual use, it is unlikely that one ONU will monopolize each wavelength, and there will be multiple ONUs for each wavelength (theoretically, up to 64 ONUs per wavelength because there are up to 256 ONUs). It will be shared.By the way, in NG-PON2, the maximum downlink and downlink is 40 Gbps (10 Gbps per wavelength).However, considering the actual usage pattern, there was a strong need for the uplink to be not so fast, and an asymmetric configuration with an uplink of 10 Gbps (2.5 Gbps per wavelength) and a downlink of 40 Gbps is also supported.The reach has been doubled from 20km on the XG-PON to 40km.Well, since the specifications have been decided, will it be widely used?From the ONU side, the speed itself remains unchanged at 10 Gbps, so there is no inconvenience even with XG-PON / XGS-PON / 10G-EPON.And there is talk that 10Gbps is not enough for base stations, especially 5G.In addition, by adding a dynamic wavelength selection function to the ONU, the cost of the ONU has definitely jumped up.This time, we explained the optical fiber standard "XG-PON" for access lines of 10 Gbps both above and below standardized as "G.9807.1" by the ITU, and "NG-PON2" standardized as "G.989".Next time, I will explain the details of the specifications of "NG-PON2" and "NG-PON2 +", which is being standardized by ITU as a successor standard.Free technical writer.We have a wide range of fields of expertise, from CPUs, memories, and chipsets to communications, operating systems, databases, and medical care.The homepage is http://www.yusuke-ohara.com/Adopted for 10Gbps access line standard "XG-PON" and NURO Hikari 10G, standardized as "G.987" by ITUNTT and OKI develop WDM / TDM-PON technology that can accommodate users with a total transmission capacity of 40 Gbps and 1024Copyright © 2018 Impress Corporation. 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