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Setting the Table for 'Wideband’ Modems

Cable operators are champing at the bit to cross a magical three-digit threshold: the 100-Megabit-per-second Internet connection.

Whatever subscribers do to fill that pipe, a 100-Mbps tier could soon be a marketing priority for cable in markets where telcos have kicked up the competitive broadband pressure.

Next week at the Society of Cable Telecommunications Engineers’ Cable-Tec Expo, one of the key topics will be how operators expect to migrate to the next generation of cable-modem technologies to provide ultra-fast download speeds.

The Data Over Cable Service Interface Specification 3.0 specification, developed by CableLabs, offers the ability to virtually bond together multiple quadrature amplitude modulation (QAM) downstream channels to act as if they were a single connection — boosting bandwidth to 100 Mbps or higher.

The spec provides for higher upstream speeds and other features, but greater downstream bandwidth is the pièce de résistance that cable operators are avidly interested in.

“The first thing cable operators worldwide have talked about is that they desperately need to increase downstream bandwidth — not just peak usage, but also average bandwidth per subscriber,” said Roger Slyk, BigBand Networks’ director of product marketing for cable Internet Protocol products. “Then, we talk about upstream bandwidth increases, as well as other things, like the transition to full IPTV.”

Wisely, the industry has started referring to the downstream channel-bonding capabilities of DOCSIS 3.0 using a more marketing-friendly term: “wideband,” which is how Comcast CEO Brian Roberts introduced his demo of a 150-Mbps cable modem at The Cable Show last month.


So when and where will wideband appear? First of all, CableLabs hasn’t yet begun the certification process for DOCSIS 3.0 gear. That’s slated to begin in October, with commercial products available next year.

Most North American operators seem willing to wait for the CableLabs seal of approval for initial “bronze” DOCSIS 3.0 gear, which will provide downstream-bonding features but lacks other pieces of the full spec. Meanwhile, some in Europe and Asia have already deployed pre-certified channel-bonding cable-modem equipment.

When asked about Comcast’s plans, Roberts demurred. Other company executives have said the operator expects to test pre-certified DOCSIS 3.0 equipment this year, with commercial deployments possible in 2008. At a press conference, Roberts said that DOCSIS 3.0 can be deployed in only those markets where a business case exists. (In other words: wherever Verizon Communications is marketing FiOS Internet service.)

Cable companies, then, are starting the DOCSIS 3.0 upgrade discussion from a business-case perspective.

“It’s going to be a competitive decision,” said Brian Wheeler, Arris Group’s director of product management for cable-modem termination systems. “It has to be an analysis of your current product offering and the competitive mix that’s countering that offering.”

The cost of an upgrade must be balanced against the expected uptake of higher-bandwidth tiers — while ensuring service to existing broadband customers isn’t more expensive to deliver, said Jeff Walker, senior director of marketing for Motorola’s Home and Networks Mobility group.

“The question is, how much bandwidth can you economically provide and still have a competitive service?” he said.

Next, operators must evaluate the readiness of their hybrid fiber-coaxial networks to accommodate DOCSIS 3.0. Most likely, each system will need to scare up some additional capacity.


Getting to 100-Mbps download speeds requires bonding at least three QAM channels, while hitting 160 Mbps takes four. (Each 6-Megahertz channel can, in theory, deliver upward of 40 Mbps.) Today, operators typically have just one downstream channel going down to each node.

“There are a whole host of issues the MSOs need to look at in moving to DOCSIS 3.0, and finding the available QAMs is a key piece,” said Douglas Fast, vice president of research and development for Vecima Networks, which sells QAM upconverters.

As Walker noted: “It’s not like cable operators have any 6-Mhz channels sitting idle — every single one of them is being used.”

Then comes upgrading the CMTS equipment to handle the greater capacity afforded by DOCSIS 3.0. Arris’ Wheeler said that’s not just a hardware upgrade; provisioning and billing systems will need to be reconfigured and tested to make sure existing service isn’t disrupted. “I need to pace that out so everyone crosses the finish line at the same time,” he said.