Cable IPTV Push Sparks Interest In Refinements to DOCSIS 3.0

John Holobinko, VP marketing, BigBand Networks

John Holobinko, VP marketing, BigBand Networks

April 13, 2009 – Does the cable industry need still another version of DOCSIS?

Debate is intensifying in cable circles over how best to accommodate distribution of growing volumes of video content over DOCSIS channels, with some players insisting there’s a cheaper way to go through adjustments in CMTS architecture and others contending IP video needs to be treated independently of the CMTS as part of the video service portfolio under control of edge-based intelligence.

Adding to the confusion, some stakeholders say there’s no need for any changes at all because the costs of CMTS downstream modules are falling rapidly and will continue to do so as ever more next-generation modules are deployed. But, while this is true, it begs the question of whether other approaches might prove even more cost effective, especially if the industry settles on a unified approach to optimizing DOCSIS for IPTV.

Thus, the question is, will CableLabs step in to develop still another version of DOCSIS, perhaps an extension of the new 3.0 version rather than a completely new version, or will the issues be left to the market to resolve? A senior executive in a position to know says the issue is on the table in discussions among CableLabs members, but there’s been no decision to launch a new initiative.

Making the case for an edge-based approach that avoids use of the CMTS, BigBand Networks recently introduced the vIP Pass platform (see March ScreenPlays, p. 8), which puts DOCSIS “wrappers” on IP video streams so that the streams can be delivered through DOCSIS 3.0 modems to end users. The strategy isn’t simply a matter of bypassing the CMTS, says John Holobinko, BigBand’s vice president of marketing. Rather, it’s about putting IP video on the same operational plane as other video services in order to establish a uniform approach to handling all types of video, regardless of which devices are accessing the content.

“The big challenge facing operators today is to be able to treat video content as a single asset,” Holobinko says. “Why reinvent the wheel by treating IPTV as a separate silo? The mechanisms you need to process this content already exist on the video side of the equation. You can treat it as just another data plane.”

Holobinko asserts this sort of extension of the applicability of edge intelligence is the biggest argument for installing the switched digital video (SDV) technology BigBand pioneered as a bandwidth-saving mechanism. Now serving some 22 million cable households, the BigBand SDV technology has positioned operators to continually expand on use of intelligence to support next-generation services, he notes.

“There are a number of ways besides SDV to grow bandwidth, but SDV puts you in a position to evolve toward switched unicast and more personalized services, including advanced advertising,” Holobinko says. “It gives you the capability to grow in steps.”

But there’s strong resistance to the CMTS bypass case on the part of companies like Cisco Systems that are pushing the envelope on DOCSIS technology. Where a year ago Cisco was demonstrating 88 downstream channels per chassis on its CMTS, it will achieve 500 downstreams by year’s end, says Ben Bekele, a marketing manager for the company. Challenged by MSOs at the end of 2007 to reach ten times the capacity on its CMTS at a tenth the cost, the company hit the cost target but exceeded the capacity goal by a factor of three, Bekele says.

Bekele also argues the DOCSIS 3.0 CMTS-based approach to delivering IP video allows operators to flexibly leverage combinations of unicast and multicast delivery mechanisms in conjunction with use of bonded and non-bonded channels as conditions require. While the industry’s TV-to-PC programming agenda presently leans toward delivery of content in on-demand mode rather than linearly, the availability of IGMP (Internet Group Management Protocol) multicasting as a function within the DOCSIS framework could be important to future IPTV configurations.

But, of course, SDV is built on the use of multicasting in the non-IP traditional digital TV broadcast mode, which presumably would be how IP video traffic would be handled through the edge-based architecture. Which way an operator chooses to go in setting up IPTV distribution may well depend on whether the company is already pursuing SDV or has chosen another approach to bandwidth conservation, such as Comcast has done with its move to reclaim most of the analog bandwidth on its networks through use of low-cost DTA (digital terminal adapter) set-tops to convert digital to analog signals in analog households.

Harmonic, which won a CableLabs innovation award for its Direct-2-Edge IPTV solution in 2007, has quietly moved the product to preparations for commercial deployment, notes Nimrod Ben-Natan, vice president of product marketing, solutions and strategy at Harmonic. “We’ll be announcing a major deployment of the technology soon,” he says.

But Harmonic has not made a big deal out of the platform, he adds, because the company recognizes it’s not the end-all solution for the industry as a whole. “It’s a great tool, a very cost-effective way to deploy IP-based video services,” he says. “But I’d be lying to you if were to tell you the CMTS market is standing still. In some cases people will prefer Direct-2-Edge, and in others they’ll stay with the CMTS approach.”

Ben-Natan notes that two and a half years ago CableLabs produced a controversial document in which the costs of the CMTS were cited as a key factor arguing for migration to all-fiber networks in order to cost-effectively achieve the level of broadband capacity that would be required to operate in IP mode over time (see ScreenPlays November 2006, p. 1). With CMTS and QAM prices now a fraction of what they were then, operators remain committed to using DOCSIS to support broadband capacity, he says.

Moreover, if CableLabs were to move toward new DOCSIS specifications, there would be a simple way to cut costs even farther than has been achieved with the decoupling of the downstream and upstream channel cards in the CMTS, which is intrinsic to DOCSIS 3.0. “You can break up functionalities that presently are integrated into one box to better capture cost benefits,” Ben-Natan says.

Building on the modular CMTS model, where QAMs are positioned at the network edge rather than in the CMTS, the industry could exploit the high processing intelligence in today’s off-the-shelf terabit routers to create DOCIS-optimized units to handle CMTS functionalities in central locations. High-density QAM modules such as envisioned in Harmonic’s HectoQAM roadmap would allow a single high-capacity router port to serve multiple RF channels at the edge.

Arris, too, has put together a DOCSIS CMTS bypass solution for IPTV, leveraging work done earlier by C-COR and nCube, two companies now folded into the Arris portfolio, but the company is not actively promoting the solution. “It would be relatively trivial for us to resurrect that environment and get it deployed if we see a demand for it,” says Joe Matarese, vice president and general manager of on-demand strategies at Arris.

“From a back-office standpoint, we really don’t care what approach is taken,” Materese says. “But it would probably be easier for operators to support IPTV on the I-CMTS platform.”

Taking a more modular approach involves integration of session management and policy management capabilities, which Arris is well equipped to do within its own platform or with other vendors, he adds. But serving the needs of an IPTV service might require more complicated interfaces than are presently supported within CableLabs’ PacketCable Multimedia specifications.

“Whatever architecture you decide on there are probably some tweaks that need to be made to support a real IPTV service,” notes the unnamed executive who was referenced earlier. “The industry needs to decide which way it wants to go and optimize the architecture accordingly. That’s where CableLabs comes in.”