by ITU News
The ITU Telecommunications standardization (ITU-T) working groups on broadband access over metallic conductors (Q4/15) and optical systems for fiber access networks (Q2/15), established in 1997 (25 years ago), laid the foundations for fixed broadband and have since then facilitated the meteoric rise in access speeds. Both groups are part of ITU-T Study Group 15, which looks at networks, technologies and infrastructures for transport, access and home.
DSL: ITU-T Q4/15 was formed to make DSL globally scalable:
“What followed was a 25-year journey of dedicated engineers fighting physics for ever-higher broadband speeds, through several generations of ITU-standardized DSL technology,” says Q4/15 Rapporteur Frank Van der Putten (a strong colleague of this author from 1996-2002 when both of us worked on ADSL and VDSL standards in T1E1.4 and the ADSL Forum).
Building on prior work by Alliance for Telecommunications Industry Solutions (ATIS) committee T1E1.4 and European Telecommunications Standards Institute (ETSI) working group TM6, the DSL technologies standardized by ITU now connect over 600 million homes and businesses to the Internet.
“DSL changed the world by enabling mass-market broadband,” Van der Putten says.
DSL enabled rapid broadband deployment at low cost because it used the existing telephone wires to the home.
“Championed at first by an impassioned few, continually provoking debates among Q4/15 experts, it has been an intellectual catalyst for the advancement of communications technology,” he adds. “We are proud to have played a part in that.”
While ADSL (asymmetric DSL), as defined by ITU in 1999, could deliver 8 megabits per second (Mbit/s), it was followed by ADSL2plus in 2003 at 24 Mbit/s and the very high speed VDSL2 at 70 Mbit/s. With the introduction of vectoring, VDSL2 reached 100 Mbit/s by 2010 and 300 Mbit/s by 2014.
In 2014, G.fast raised the bar to 1 Gbit/s, doubling this to 2 Gbit/s in 2016. Its successor standard, MGfast, achieves an aggregate bit rate up to 8 gigabits per second (Gbit/s) in Full Duplex mode and 4 Gbit/s in Time Division Duplexing mode.
The architecture standards for DSL, G.fast and MGfast were defined by the Broadband Forum (once known as the ASDL forum), which also plays a key part in promoting interoperability.
Van der Putten explains: “Both technologies intend to meet service providers’ need for a complement to the fibre-to-the-home technologies in scenarios where G.fast or MGfast prove the more cost-efficient strategy.”
The continual upgrading of ITU’s standards has also sparked huge upward revisions in forecasts for the life left in traditional telephone wiring.
Future directions for Q4/15 work include G.fast-based backhaul, MGfast at aggregate data rates of 10 Gbit/s, and ultra-low latency transmission optimized for 5G wireless back/mid-haul, he says.
Cost-efficient fiber access – PON and FTTH:
ITU-T Q2/15 paved the way for passive optical network (PON) technologies as a highly cost-efficient means of enabling FTTH. Optical access networks now serve over a billion users worldwide, mostly based on PON. Q2/15 works closely with Full Service Access Network (FSAN), which collects system requirements from operators to determine common requirements for ITU standards.
“The result has been systems ideally suited for a large group of networks and applications,” says Q2/15 Rapporteur Frank Effenberger.
“The first widely deployed system, G-PON [Gigabit PON], is found almost everywhere now,” he adds.
Q2/15 has developed seven generations of PON systems. The first, pi-PON, operated at 50 Mbit/s. This was followed by A-PON (155 Mbit/s), B-PON (622 Mbit/s), G-PON (2.5 Gbit/s), XG(S)-PON (10 Gbit/s), and NG-PON2 (4 x 10 Gbit/s).
To provide the basis for interoperability, ITU standards specify the control system for PON systems. Q2/15 has also developed a range of implementer’s guides and works closely with FSAN, ATIS, and the Broadband Forum to foster common designs and interoperability.
From 10 to 50 Gbit/s PONs:
Demand for higher capacity keeps growing fast. Optical access solutions also support 5G wireless communications and innovation for smart cities and factories.
“What we are seeing is a gradual evolution from G-PON to XG-PON [a 10G, or 10 Gbit/s, network] and XGS-PON [a 10G symmetric network], which is now being deployed at scale in many countries,” says Effenberger.
The latest generation of ITU-standardized PON, known as “Higher Speed PON”, provides for speeds of 50 Gbit/s per wavelength, up from the 10 Gbit/s of its predecessors. Market demand for Higher Speed PON is expected to begin in 2024.
“Given the large size and cost of the fixed access network, upgrades generally come once per decade,” says Effenberger.
Higher Speed PON includes both single-channel 50 Gbit/s systems to succeed XG(S)-PON and multi-channel 50 Gbit/s systems to succeed today’s NG-PON2 – a 40G PON that operates at 10Gbit/s per wavelength.
Although Higher Speed PON offers a five-fold capacity increase over its predecessors, it has been designed to work with the same fibre plant as G-PON, XG(S)-PON and NG-PON2.
“A successful technology requires a coincidence of both technical feasibility and strong global market demand,” notes Effenberger. “We strongly believe that 50G PON will provide the right capacity, at the right price, and at the right time.”
All-fiber future at Gbit/s speeds:
Q2/15 aims to continue delivering higher-capacity PON solutions, such as a multi-wavelength version of Higher Speed PON, and speeds even higher than 50 Gbit/s on a single wavelength. But passive networks cannot handle all foreseen demand.
“Certain applications will require more dedicated and higher-capacity solutions than PON,” says Effenberger, highlighting the motivations behind Q2/15’s development of various point-to-point bidirectional optics with speeds of 1 Gbit/s, 10 Gbit/s, 25 Gbit/s, and 50 Gbit/s.
Q2/15 continues to study 100 Gbit/s transmission and point-to-point wavelength connections over a shared optical distribution network based on wavelength division multiplexing. “These are likely to find use in wireless fronthaul applications, given their exacting latency requirements,” says Effenberger.
Fiber and cable networks are dominating the global broadband market, with the technologies now servicing 77% of fixed subscriptions, new figures from Point Topic have revealed.
According to the Global Broadband Statistics, which take into account subscriptions up to the end of 2017, more than 50% of people in more than 40 countries, including Singapore (97%), China (89%), United States (87%), and the UK (55%), are connected via full-fiber, fiber-fed copper or cable.
Point Topic Research Director Dr Jolanta Stanke told the Broadband Forum:
“We are finding that customers across most global regions increasingly prefer faster broadband services delivered over fiber and cable platforms, as opposed to ADSL. This trend will continue as more bandwidth-hungry young consumers become paying decision makers, even though superfast 4G LTE and 5G mobile broadband services will compete for their wallets.”
Fiber-fed subscriptions – including Fiber-to-the-Home (FTTH), Fiber-to-the-Building (FTTB), Fiber-to-the-Cabinet (FTTC), Very High Bitrate Digital Subscriber Line (VDSL), VDSL2 and G.fast – accounted for 57% of broadband subscriptions, with more than 530 million connections. Stanke agreed VDSL and Gfast were together largely responsible for the growth that fiber has seen, with more than 30 operators across all continents deploying or trialing G.fast.
“G.fast gives operators a more cost-effective variant of fiber that will be used by operators who want to upgrade their existing networks quicker and more easily,” she added. “This could enable them to serve more customers in less densely populated areas, where direct fiber investment is less economically feasible.”
In total, cable, including hybrid fiber-coaxial, accounted for 20% of all fixed broadband connections. According to the report, the latest standard of this technology is currently deployed across several markets, being especially popular in North America, and can deliver gigabit download speeds.
Broadband Forum CEO Robin Mersh said the figures reflect the fact that new technologies that let operators deploy fiber deep into the network without having to enter buildings themselves are quickly moving from trials to mass deployment.
“If operators want to deliver competitive broadband services, maximizing their investments through the use of technologies like G.fast is vital,” said Mersh. “Expanding the footprint of their existing fiber networks in this way is cost-effective and delivers the gigabit speeds consumers crave. The growing trend towards fiber, whether its fiber-fed copper or full fiber, and cable deployments highlighted by Point Topic’s report confirms that the Forum’s work on interoperability and management of ‘fiber-extending’ technologies is vitally important.”
The voracious demand for connectivity is evident in the increased demand for fiber, cable and coax despite the parallel growth of LTE and MAYBE (?) “5G.”
Though “5G” is in currently proprietary to each wireless network operator, huge investments in fiber, coax and copper are being made because strategic planners expect 5G to be mainstream in the next several years (we think NOT until late 2021 at the earliest when IMT 2020 recommendations are finalized and implemented in base stations and endpoint devices.
Last month, Broadbandtrends’ Global Service Provider G.fast Deployment Strategies surveyed 33 incumbent and competitive broadband operators from across the globe. The market research firm found that four in five service providers have G.fast plans for this year and that 27% are in active deployments. AT&T is a huge supporter of G.fast while Verizon is not.
About the Broadband Forum
Broadband Forum, a non-profit industry organization, is focused on engineering smarter and faster broadband networks. The Forum’s flagship TR-069 CPE WAN Management Protocol has now exceeded 800 million installations worldwide.