Cable technologists embrace DAA as a complement to DOCSIS 3.1, fibre deep and other technologies
ATLANTA – Believing their industry's hybrid fibre-coax (HFC) networks have plenty of life left in them, cablecos are pushing forward with distributed access architectures (DAA) designed to enable them to boost capacity for gigabit and other advanced services.
Speaking here at the annual SCTE Cable-Tec Expo show last week, top cable technologists from North America and Europe said they are turning to on DAA and new versions of the industry's DOCSIS broadband specs to meet the bandwidth demand with their existing networks. Rather than junk their legacy HFC systems and go fibre-to-the-home with PON technology, they are largely pursuing ways to supercharge those legacy systems and squeeze ever-greater operating efficiencies out of them and DOCSIS technology.
"Co-ax does have a lot of life," said Doug Jones, principal engineer at CableLabs, speaking during a pre-show session primarily focused on DAA. "The DOCSIS technology is not out of gas in any way, shape or form."
DOCSIS 3.1, the latest version, already enables cablecos to deliver up 10 Gbps downstream and 1 Gbps upstream on existing plant built out to 1GHz spectrum. Then the next version of DOCSIS coming down the pike, known as Full Duplex DOCSIS, will support symmetrical speeds as high as 10Gbps. In addition, as Jones intimated, the industry is now looking at yet another potential spec, known Extended Spectrum DOCSIS, that would allow operators to offer speeds of 30 Gbps or higher using spectrum above the current the 1 GHz ceiling.
Thanks to the steps already taken, cable operators now offer 1-Gig service to 56% of U.S. cable homes, according to Jon Schnoor, lead engineer for CableLabs's wired technology team. That's up from a mere 4% of U.S. cable households just 18 months ago.
However, even with the forthcoming Full Duplex DOCSIS standard, cable operators will need more help to serve the continuously surging customer demand for more bandwidth. That's where DAA comes in. Under that concept, operators will shift at least some of the "smarts" of their system from the cable headend to the access network and thereby closer to customers, thus enabling them to offer higher-bandwidth services.
Specifically, DAA calls for moving elements of the PHY (physical) layer, as well as possibly the MAC (media access control) layer, from the cable headend to the optical-fibre node in the access network, which is where the fibre connects to the co-ax and cable signals switch from optical to electrical. Schnoor said such a shift to the node will be crucial for cablecos to deploy gigabit services everywhere economically and at scale.
To ease that shift, CableLabs and its members now have a Distributed CCAP Architecture (DCA) project well underway. Schnoor said the general idea here is taking cable's traditional centralized CCAP (converged cable access platform) design and "blowing that up." He noted that the shift to a more distributed model will cut cable operators' needs for space, power and cooling, thereby reducing their operating expenses.
One DAA option, known as Remote PHY, is viewed as the first, and easiest, step for operators to take. "We had to start somewhere, and Remote PHY was really it," Schnoor said. He said CableLabs' emerging Remote PHY specs are nearly finished, with the industry R&D group now conducting equipment interoperability testing with about two dozen different vendors.
So far, CableLabs has come out with eight specs for different Remote PHY elements, with more quarterly interops still scheduled to take place. Schnoor said the aim is to get it all the various elements stable enough so that vendors can begin preparing their Remote PHY Devices (RPDs) ready for qualification testing and approval by CableLabs. At the same time, CableLabs is also working on developing specs for its Flexible Mac Architecture (FMA), a new name for what used to be known as Remote MAC/PHY.
While some cable operators have already begun testing Remote PHY in the field, Schnoor said, next year should be the year when MSOs will "ramp up" deployments. Several industry analysts have issued similar forecasts.
Canada's two biggest cable operators, Shaw Communications and Rogers Communications, are among those on the front lines with DAA service trials and deployment plans. Shaw, for instance, is now gearing up for a DAA field trial in an undisclosed location next month after doing prep work for the trial over the past year and examining the potential capacity gains of making such a shift. (Cartt.ca will have more on this, soon, as we know of an independent cable operator also pursing this.)
"We're moving to a high-touch trial," said Jamie Brown, director of next generation access network technology for Shaw Cablesystems. "We'll scale these nodes in about six months."
