Telco Group Pushes VDSL Spec

Cable operators concerned about telco competitors that are aggressively rolling out video services using very-high-speed digital subscriber line (VDSL) technology can rest easy — for now — as widespread VDSL deployments languish.

But an ambitious standards group, the FS-VDSL Committee, is moving swiftly to define an interoperable, end-to-end VDSL network.

"By year-end, we want to create full interoperability systems to kick off VDSL," said Clayton Mangione, president of the FS-VDSL Committee and director of technology development and convergence for Bell Canada. "The industry is just waiting for this interoperability to take place."

"There's no reason for the cable industry to have a relationship with that household," once standardized gear comes to market and telcos can place set-top boxes in the home that can deliver voice, video and data, Mangione said.

The FS-VDSL Committee is an offshoot of the Full Service Access Network (FSAN) group, which reports to both the European Telecommunications Standards Institute (ETSI) and the American National Standards Institute (ANSI) and makes recommendations to the International Telecommunications Union (ITU).

The FS-VDSL Committee is defining the components of a VDSL system from the central office to the customer premises.

Members of the nearly 50-member group include service operators Qwest Communications International Inc., SBC Technology Resources, British Telecommunications plc and Deutsche Telekom AG; as well as vendors Alcatel Alsthom, Lucent Technologies, Motorola Inc., NextLevel Communications Inc., Broadcom Corp. and Pace Micro Technology plc.

The system's starting point is Band Plan 998, the spectrum allocation for copper twisted-pair wiring that's optimized for asymmetric VDSL service. It's designed to be compatible both with ADSL, or asymmetric digital-subscriber line, and "plain old telephone service," or POTS.

FSAN adopted five bands: two upstream, two downstream and one optional.

Much of the industry is waiting for Band Plan silicon to become available, said Mangione. That's expected to happen in the third or fourth quarter of this year.

The availability of these chips and their integration into set-tops and modems is expected to bring down the cost of customer-premises equipment and spark wider VDSL deployment.

The VDSL network envisioned by the committee is a combined fiber and copper architecture designed to push 30 megabits of data per second — or more — along the downstream path. Copper loops are shortened to between 3,000 and 4,000 feet.

Mangione said the system's components comprise of a headend that takes a digital broadcast signal and encodes it according to the MPEG-2 (Moving Pictures Expert Group) standard. The compressed video is then carried over either Internet-protocol or asynchronous transfer mode (ATM), depending on the operator's architecture.

Also specified for processing at the headend is information related to customer and service management, conditional access and network-element management. The FS-VDSL Committee is creating an API (application-programming interface) for program-guide and billing interfaces to allow a software vendor to develop a platform that integrates these functions.

Aggregated into the digital video is an Internet feed, and operational support and service (OSS) data at the broadband (or host) digital terminal. Voice-over-DSL or voice-over-IP may also be mixed into this signal.

The aggregated stream is then sent either by a fiber OC-3 link (at 155 megabits per second) or a fiber OC-12 link (at 622 megabits per second) to the neighborhood digital-subscriber-line access multiplexer (DSLAM), in which copper loops extend from line cards to set-top boxes. One particular line card can serve one or several customers.

POTS traffic, usually carried separately from a class-five switch, is mixed in at the DSLAM. At the customer premises, the FS-VDSL Committee has allowed for both a distributed and centralized signal distribution model.

The centralized model specifies that one integrated set-top/VDSL modem with multiple MPEG-2 decoders be located at the home's primary TV. The device includes Ethernet connectivity to deliver Internet service to personal computers or Internet-protocol appliances. (Universal serial bus, HomePNA or other wireless connectivity may also be used.)

Existing coaxial cable is used to connect other TVs to the signal.

The set-top in this configuration serves as a "mini-headend," able to serve up several simultaneous video channels, depending on the available bandwidth. Each channel may contain its own program guide, "favorites," and parental control.

The distributed approach calls for a VDSL modem located at a hub in the home with separate set-tops for each TV.

Mangione said Bell Canada uses the centralized model in its current VDSL trial with a multiple-dwelling unit building in Toronto. The technical pilot will be expanded to market trials in between 10 and 12 Toronto buildings later this year.

The video-delivery system as outlined by Mangione is based on switched digital video, where intelligence at the DSLAM and set-top — once a user has been authorized to access a channel — brings individual "virtual" channels down the network. In a cable network, by contrast, all channels are zipped down the network.


The VDSL framework, as outlined by the FS-VDSL Committee, is essentially the network architecture that Qwest has deployed in its Next Level platform in Phoenix. Qwest officials declined to be interviewed for this article, and the company has generally been silent about its VDSL plans.

Despite its stealth mode, Qwest is by far the most prominent VDSL adopter. At a March meeting of the FS-VDSL Committee, a Qwest executive told the group that the Denver-based telco has passed 450,000 homes in Phoenix with its VDSL deployment and is offering between 190 and 260 digital-video channels, along with high-speed data and integrated telephony service.

The executive said Qwest has 50,000 subscribers in Phoenix. The telco is also offering its VDSL service, dubbed Choice TV, in selected areas of metro Denver, the home of cable incumbent AT&T Broadband.

Most other U.S. VDSL deployments have been limited to small, rural areas served by adventurous local or regional telecom companies, such as the South Carolina-based Horry Telephone Cooperative (HTC). The company, according to director of marketing Tom Vitt, is building a VDSL network in the Barefoot Landing development in the northern part of the state to serve both single-family homes and multiple-dwelling units.

"We saw this as a real opportunity to set HTC and Barefoot Landing apart," Vitt said. "We're delivering as many services as economically as we can."

HTC presently markets telephone service and 60 channels of digital video, with plans to roll out high-speed data services later this summer. All of those services will be pumped though a single gateway set-top from Next Level.

While FS-VDSL member Qwest is the Baby Bell most intimately involved with VDSL, Verizon Communications also has an interest in delivering video via copper, although it hasn't settled on a technology, said Verizon spokesman Larry Plum.

Meanwhile, a top five MSO in an urban market is testing VDSL technology to bring broadband connectivity to high-rise buildings in its territory, said Chris Britton, president of VDSL Systems. Verizon Avenues, Verizon's in-building telecom service, is also testing VDSL Systems gear.

Meanwhile, the FS-VDSL Committee is planning to demonstrate interoperability between VDSL transceivers from different chip vendors sometime in September or October.

Despite earlier messages to the contrary, telcos clearly have not abandoned the video leg of the triad of bundled voice, video and data services. If the goals of the FS-VDSL Committee are met, a formidable competitor may enter cable's turf.