While fiber to the home (FTTH) remains the premier approach for gigabit broadband provision, plenty of service providers continue to look for ways to avoid the cost of an all-fiber deployment. Options such as VDSL2 and 3G wireless still don't have the necessary horsepower, we've seen. However, new classes of wireline and wireless technology have emerged that may postpone FTTH investments among some carriers.
Is G.fast fast enough?
Vendors have touted G.fast, based on the ITU-T Recommendation G.9700 family, as the pathway to gigabit over twisted-pair copper and, recently, coax. However, while several vendors say they have managed to support gigabit links via G.fast in the lab, we haven't seen such speeds in the field so far.
One aspect of G.fast is that the technology creates a pool of capacity that must be shared by upstream and downstream traffic. On the face of it, this would imply that, to support gigabit in the downstream, the total pool must be greater than a gigabit – and perhaps at least 2 Gbps if you want to deliver symmetrical gigabit service.
However, the ITU-T recently completed specifications work on a technology called Dynamic Time Assignment (DTA) that offers flexibility in the use of available upstream and downstream capacity based on expected use. So the total capacity needed to support symmetrical gigabit services should be significantly less than 2 Gbps.
Typical G.fast deployments use an architecture called fiber to the distribution point (FTTdp). As the name implies, a fiber connection (often based on PON, for future evolution to fiber to the premises) runs to a distribution point node in the field, where the optical signal is converted to electrical and served via a copper-based connection. The distribution point can be anywhere between the central office and the customer – including in the basement of apartment and other multi-tenant buildings. In fact, G.fast is finding its most widespread use as a means of serving high-speed broadband to apartment dwellers via existing in-building twisted-pair or coax wiring. In the U.S., CenturyLink and Windstream have announced they are using G.fast for this purpose. AT&T is expected to follow suit as well.
But there's no reason G.fast couldn't be used in the outside plant – and it is, notably in a pair of deployments in Europe. Both BT and Swisscom have embarked on trial and production deployments of G.fast in fiber to the cabinet (or, as Swisscom terms it, "fiber to the street") architectures. BT, for one, doesn't appear to view G.fast as an immediate pathway to gigabit broadband, however. Company sources have called for the technology to deliver 500 Mbps within the next 10 years. That timetable could accelerate, of course, with the addition of DTA and other technologies, such as channel bonding.
DOCSIS does it
Cable operators have increased their use of FTTH as a complement (or in some cases, an alternative) to their traditional hybrid fiber/coax (HFC) networks over the past few years. However, advances in DOCSIS technology may limit FTTH to greenfield and specialized applications for the foreseeable future for some operators.
For example, several U.S. cable operators have launched 1-Gbps downstream services by bonding DOCSIS 3.0 channels. Suddenlink (now part of Altice USA), Mediacom, and Cable One are among the service providers who have taken this approach.
But the primary gigabit broadband engine for cable operators will soon be DOCSIS 3.1 technology. With initial specifications in place from CableLabs, DOCSIS 3.1 promises downstream capacity of approximately 10 Gbps and upstream in the neighborhood of 1 Gbps – or, more or less the same rates as XG-PON1.
The primary technical advances within DOCSIS 3.1 is the use of Low Density Parity Check forward error correction instead of Reed-Solomon, the use of orthogonal frequency division multiplexing (OFDM) modulation, the support of multiple modulation profiles, and use of additional spectrum (as well as improved use of existing spectrum).
The technology supports channel bonding as well; in fact, as the technology is designed to be able to run alongside DOCSIS 3.0, operators are expected to bond DOCSIS 3.1 and 3.0 channels together.
Several operators have begun DOCSIS 3.1 deployments, with Comcast leading the way in the U.S. and Liberty Global doing the same in Europe. Comcast, in fact, believes it can use DOCSIS 3.1 to support its 2-Gbps Gigabit Pro service. Other operators, such as Mediacom and WOW!, have launched deployments as well, with Cox and Charter expected to follow very soon.
Of course, this initial implementation of DOCSIS 3.1 leaves in place the approach's main weakness versus FTTH – more trouble supporting high-speed symmetrical services. Particularly with business services support in mind, CableLabs has launched an effort to develop specifications for Full Duplex DOCSIS 3.1, which would support 10 Gbps in both directions.
CableLabs and the operators its serves appear to see DOCSIS 3.1 as a long-term answer for gigabit and beyond. The group recently revealed that it has begun investigating the use of coherent transmission technology for the "F" portion of the HFC network, to enable the feeder network to keep up with the demands that DOCSIS 3.1 will create without requiring additional fiber.
Here comes fixed wireless
Wireless technology, particularly fixed wireless, has made rapid strides as a broadband delivery mechanism over the past year in the eyes of service providers.
Perhaps the most salient example of this trend is Google Fiber's adoption of the technology. Frustrated by the red tape that has surrounded its FTTH efforts, not to mention take rates that reportedly haven't lived up to expectations, Google has purchased broadband service provider Webpass, which uses fixed wireless to serve multi-tenant buildings. The company subsequently called a timeout in several of its previously identified FTTH markets as it ponders whether a wireless strategy might create a better business model.
Meanwhile, mainstream service providers also are looking at adding fixed wireless to their broadband delivery portfolios. AT&T, for example, has launched a trial of point-to-point millimeter-wave wireless to deliver 100-Mbps broadband to multiple apartment complexes in Minneapolis – a territory in which it currently doesn't provide service.
In the trial, AT&T delivers fiber-based broadband to a central location. That location is then connected to subscriber buildings using "multi-gigabit" millimeter-wave links. At the subscriber building, the signal is converted from wireless to a format that AT&T can transmit to individual units using existing in-building wires (or new wiring if necessary). Subscribers then can access the service by plugging their Wi-Fi routers into existing wall jacks.
The company didn't immediately target gigabit broadband as a goal for such an approach – in fact, it mentioned 500 Mbps as a next step. However, earlier this year, AT&T said it expects to deliver 1 Gbps over its 4G network and has demonstrated 14-Gbps transmission and latency of less than 3 ms via 5G technology in its labs. It expects to begin field trials of video delivery via 5G this year.
So it seems only a matter of time before wireless becomes a true competitor to FTTH in the battle to dominate gigabit broadband services delivery.