TP-Link releases "Tapo L900-10", a 10m version of a smart Wi-Fi tape light that can be cut to any length.Since NTT Higashi 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, we will explain the 2.488 Gbps access line standard "G-PON" standardized by the ITU as "G.984.1 / 2/3/4".(Editorial department)The specifications of "E-PON" and "GE-PON" (which is referred to as "G-EPON" in the IEEE) were established by the IEEE, but the ITU established another standard in parallel with this. Was.That is "G-PON".G-PON is the successor standard to "B-PON", which was started in 2001 by "ITU-U (International Telecommunication Union Telecommunication Standardization Sector)" (International Telecommunication Union Telecommunication Standardization Sector).As introduced in the first article, B-PON has been standardized as ITU "G.983.1" to "G.983.4".The standardization plan for G.983.4 was approved in December 2001, but the work has shifted to the standardization of G-PON in earnest.The first draft was published in May 2002, with "G.984.1" and "G.984.2" approved in 2003 and "G.984.3" and "G.984.4" approved in 2004 for standardization. It has reached.The newly established "GTC frame" was adopted as the protocol.As mentioned earlier, the story of using ATM frames for B-PON and Ethernet frames for GE-PON is as introduced above, but G-PON is basically an ATM-based fixed-length frame that follows the flow of B-PON. It becomes communication.However, an ATM frame with a short frame length has the disadvantage that the number of frames is unnecessarily increased.Therefore, in G-PON, instead of inserting the Ethernet frame into the ATM frame as it is, the "GEM (G-PON Encapsulation Method)" based on the general-purpose frame defined in "G.7041 / Y.1303" of ITU-T ) Frames were converted once, and this was switched to a fixed-length frame called a GTC (G-PON Transmission Convergence) frame.The GTC frame length is defined by time, not size, and is 125 μs.In other words, in the case of 2.488 Gbps, the size of one GTC frame is 312,500 bits, which is about 38 KB.This is large enough to store multiple Ethernet frames with a maximum length of 1500 Bytes.In fact, multiple GEM frames and ATM frames (maybe because of communication other than Ethernet, or ATM frames can be used) can be stored in the GTC frame.Since the OLT side exchanges in units of this GTC frame, the processing overhead is significantly reduced compared to B-PON.The wavelengths used are 1260 to 1360 nm for uplink and 1480 to 1500 nm for downlink (OLT → ONU).In B-PON, the downlink was 1480 to 1580 nm, but considering that the band for video distribution is superimposed on 1550 to 1560 nm, it is limited to 1500 nm.In addition, when the transmission distance exceeds 20 km, an error correction code called "FEC (Forward Error Correction)" will be added.As a whole, can it be said that the specifications are particular about the technology of sending fixed-length frames while considering the era of Ethernet?By the way, in G-PON as well, the use of "DBA (Dynamic Bandwidth Assignment)" is considered as in GE-PON.However, unlike GE-PON, it uses "T-CONT (Transmission Container)" to control the timing of transmission and the amount of data for each ONU.In this way, G-PON was able to take a wider bandwidth than GE-PON while technically crushing the negative elements of B-PON.It is not mentioned as a merit because speed is prioritized in Japan, but since there are not a few services of several Mbps even in FTTH overseas, the maximum capacity of 254 ONUs and the maximum reach of 60 km are It was particularly popular in North America because it was effective in reducing costs on the part of vendors.Then, is there any example of adoption in Japan?That's not the case.So-net (currently Sony Network Communications) at that time has been developing "NURO Hikari", a service of 2 Gbps downlink / 1 Gbps uplink using G-PON since 2013.There is an interview article here about this, and if you read this, you can understand "Why So-net chose G-PON at that time".However, in Japan, there is no other provider that follows G-PON and adopts it, and So-net itself has shifted to "XG-PON" after this.As mentioned above, it seems that there was no particular cost disadvantage because it is a standard that is widely used overseas and there are many equipment for ONU and OLT overseas.This time, I explained the access line standard "G-PON" using 1 Gbps optical fiber standardized by ITU as "G.983.1 / 2/3/4".Next time, I will explain the optical fiber standard "10G-EPON" for 10Gbps access lines standardized as "IEEE 802.3av".Free technical writer.We have a wide range of fields of expertise, from CPUs, memories and chipsets to communication-related, OS, databases, and medical-related fields.The homepage is http://www.yusuke-ohara.com/Copyright © 2018 Impress Corporation. 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