By: Fred Dawson
Japan’s largest cable MSO is exploring new techniques for delivering data at speeds of 100mbps and above in response to the challenge posed by 100mbps fiber-based services from Nippon Telephone, Telegraph and other entities.
In what amounts to a preview of how cable operators everywhere are likely to respond to telcos’ expansion to fiber capacity in the years ahead, Jupiter Telecommunications is experimenting with a new “wideband” system developed by Cisco Systems Inc. as a prototype for DOCSIS 3.0, the very high-speed version of the Data Over Cable Service Interface Specifications now under development at Cable Television Laboratories.
At the same time J-COM is looking at the use of fiber in conjunction with an in-building distribution system that would provide support for delivering 100mbps service to multidwelling units, using existing coaxial cable to send the stream to customers on a shared basis.
While the in-building solution would address an immediate competitive need for J-COM, a wideband approach such as the one Cisco is offering will give operators the capacity to deliver IP-based services at speeds of 1gbps and more. Sources report CableLabs is coming under increasing pressure to deliver DOCSIS 3.0 specs, with the latest prognosis calling for completion of a draft for circulation to members by year’s end and possible commercialization some time in 2006.
However, for J-COM and perhaps for other cable operators who experience early fiber or VDSL2 (very high-speed DSL) rollouts in their territories in the months ahead, commercial availability of a standardized approach to expanding their broadband bandwidth may not come soon enough. “It’s a real issue for us as to whether we should proceed with a proprietary system or wait for the standard,” says J-COM CEO Greg Armstrong. “We are taking a hard look at the Cisco system.”
Basically, Cisco’s Wideband Protocol involves integration of multiple digital cable channels or “QAMs” (in reference to the role quadrature amplitude modulation plays in increasing channel bit rates) into a single high-capacity channel that can operate at 100s of mbps as opposed to the 38mbps that any single 6MHz channel can deliver over today’s cable systems. The concept tops earlier channel-sharing approaches to expanding throughput over DOCSIS by breaking up the transmission frames into fragments and “stacking” them so that all fragments are transmitted simultaneously across all the integrated channels. This cuts the time it takes to deliver the frame to a tiny fraction of what it would take to deliver the frame over a 6MHz channel.
As proposed by John Chapman, a distinguished engineer at Cisco, the Wideband Protocol could be used not only for Internet data but also to create a pathway for IPTV over cable networks where the single wideband stream would carry the equivalent of hundreds of digital TV programs. Addressing a recent conclave of cable engineers, Chapman called on the cable industry to adopt a goal of operating a 1gbps IP channel within five years. That speed would consume the equivalent of 24 regular cable channels, leaving 75-80 percent of the 860MHz cable network capacity untouched. “Twenty-five percent (of capacity) five years from now for IP services is not unreasonable,” Chapman asserted.
Using the wideband approach would give J-COM a way to trump the highly publicized 100mbps Internet service NTT is offering in single-dwelling and multidwelling environments. But, for now, the biggest challenge is to at least match what NTT is doing in MDUs, where users share the total 100mbps capacity that comes into the building over fiber and is distributed inside via VDSL. While pushing fiber to every single-dwelling home is not in cable’s game plan, operators can sometimes justify the costs of extending fiber to a building where dozens of potential customers reside.
“The buzz word in Japan is 100mbps,” Armstrong says. “But if you’re a fiber service customer in an MDU, you’re sharing that bandwidth with a lot of people. What we’ve found monitoring various Web sites is that 80 percent of the fiber-to-the-premises customers are experiencing actual throughput speeds in the 18-20 megabit range.”
The trick for J-Com is to give all its customers in the building shared access to the 100mbps, since that is all NTT is doing. To do that, the company needs to run fiber to the building and then be able to get a 100mbps stream onto the in-building coaxial cable. This means it has to find a way around the 6MHz channelization scheme within the 750MHz of bandwidth that is usually employed for delivering cable services.
The company is testing an in-building distribution platform that puts the 100mbps data feed onto the coax spectrum above 800MHz, out to about 1GHz, Armstrong says. This is tricky because, at the high end of the spectrum signals tend to break up faster than they do at lower frequencies, which shortens the distance they can travel on unamplified in-building wiring.
“So far (the system) is working very well, but it’s new technology, so there isn’t any real market experience to go on,” Armstrong says. “The concern I have is operating at those high frequencies and the distance limitations you can run into. But we’re getting a steady 50-60mbps throughput per user, so it’s encouraging.”
