FEATURE STANDARDS
Table 1: Passive optical network standards
Technology BPON EPON GPON
10G-EPON XG-PON NG-PON2 NG-EPON
Future optical access systems
Standard
ITU-T G.983 IEEE 802.3ah ITU-T G.984 IEEE 802.3av ITU-T G.987 ITU-T G.989 IEEE 802.3ca ?
Year first approved 2001 2004 2004 2009 2010 2015
(2019) (2021)
Downstream bitrate 622 or 1244 Mb/s 1.25G 2.5G 10G 10G 40G
25, 50 or 100G ?
Upstream bitrate 155 or 622 Mb/s 1.25G 1.25G
1 or 10G
2.5 or 10G 10G
25, 50 or 100G ?
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wavelengths or bonding wavelengths that are already there to give bigger single peak rates or capacity,’ he explained. Te standards development process can take
advantage of efforts in other parts of the optical industry to develop faster and lower cost optical technologies, particularly within Ethernet. For example, the IEEE P802.3ca 100G-EPON Task Force, which began work in December 2015, is currently working on a model for 25G operation over a single wavelength (with four wavelengths yielding an aggregate capacity of 100Gb/s). Historically, ITU-T standards-based PON
Group. While operators in some of the more mature FTTH markets are looking to move to next-generation technologies sooner, it is likely that only the ‘power users’ on those networks would opt for the higher broadband speeds they provide. In its market forecast released in 2016, Ovum estimates that the number of GPON optical line terminal (OLT) ports shipped in 2021 will be 10 times the volume of all other ITU-T type next-generation PON ports combined. ‘Tis does not mean there will be no
meaningful market for next-generation PON systems,’ he added. ‘However, any future roadmap must take into account the wider market beyond residential services, such as business leased line services or mobile backhaul and fronthaul applications.’ Operators expect to increase their revenues by mixing residential and business users or mobile cell sites on a common access infrastructure. NG-PON2 systems were already designed with such converged services in mind, but business and mobile service requirements continue to evolve. Whereas 100Mb/s services were common
among small to medium enterprises, Gigabit Ethernet services are becoming increasingly popular. ‘Typically, business users expect their services to provide symmetric bandwidth, and this was a strong motivation behind the recent standardisation in the ITU-T of XGS-PON,’ Nesset said. ‘Revenues from such premium services may be sufficient to justify the higher cost of next-generation systems.’ Mobile fronthaul – connecting remote radio
heads to the baseband equipment – has also been a hot topic of discussion among FSAN members for several years. ‘Certain Asian operators are very interested in converging mobile traffic onto their PON network … because they have a high volume of deployed
30 FIBRE SYSTEMS Issue 14 • Winter 2017
fibre in the access, so it makes sense to reuse it for those kinds of applications,’ explained Dawes. Te transport of mobile fronthaul was a key motivation behind the specification of point-to-point wavelengths in addition to the time-division (TDM) based channels in the NG-PON2 standard. In future, mobile fronthaul could be packet-based, and so could be transported on sufficiently high-capacity TDM channels in a PON.
Roadmap themes Te new roadmap highlights peak rates to individual end users of greater than 10Gb/s, to serve business customers and mobile operators. Tere are several ways to approach this goal, according to Dawes. ‘Te next steps could be increasing the bit rate on wavelengths that are already defined, adding some more
bit rates have advanced in multiples of 2.5, so a step from 10G to 25G operation seems logical. Right now, however, all options are still open. ‘We’re not necessarily going to 25G straight away,’ Dawes said. ‘It may even be that we look at just a small step from 10G to 12.5G or 15G. It’s going to be partly driven by what components are available and what we can do with different modulation schemes … things of that sort.’ Purely increasing the bit rates and capacity
are not the only consideration in the evolution of optical access standards, however. Operator requirements that have been broadly agreed appear on the roadmap under five themes: availability, flexibility, peak rate, capacity and reach. Protection and resilience, in particular, are going to become increasingly important, given that next-generation PONs will be expected to carry high-value services such as business and mobile traffic. Even residential
FSAN Standards Roadmap 2.0 (released November 2016)
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