De-Bottlenecking HFC: Still A Slog, Despite Big Advances

Stan Brovont, CMO, ARRIS

Stan Brovont, CMO, ARRIS

November 30, 2012 – Long awaited advances in two closely linked next-generation cable platforms as well as a third that’s coming out of left field have set the stage for making standards-based TV-to-IP migration a reality, but it could be quite a while before anything like a wide-scale push in this direction materializes.
The first commercial iterations of elements fundamental to the new Converged Cable Access Platform (CCAP) together with private demonstrations of full-scale CCAP prototypes promise a game-changing way to dynamically set spectrum allocations for MPEG-2 and IP streams on each QAM (quadrature amplitude modulation) port as well as to more efficiently define service groups by service categories rather than by geographic sub-divisions. At the same time, as revealed by CableLabs and the Society of Cable Telecommunications Engineers at the recent Cable-Tec Expo in Orlando, the latest version of the Data Over Cable Service Interface Specifications, DOCSIS 3.1, has emerged as a path to expanding capacity over the hybrid fiber-coax (HFC) network to up to 10 gigabits per second downstream and 1 Gbps upstream.

Paralleling the DOCSIS 3.1 work but on a separate track is the emerging IEEE standard known as Ethernet Passive Optical Network Protocol over Coax (EPoC), more formally designated as IEEE 802.3bn, in which CableLabs is now a full-fledged participant. This summer EPoC cleared the IEEE’s Project Approval Request process with the assignment of a formal working group, which expects to complete its draft specifications by next November. Assuming the draft is approved by members, the group expects to submit the specs for final approval as an IEEE standard by August 2014.

The question now is, when will all this begin to make an impact on cable operators’ ability to break free of current platform encumbrances on their flexibility to deliver IP-based content and applications on all interfaces with the customer, including the TV set? Despite some aggressive scenarios posited in various tech corners, with so many moving parts to deal with, anything approaching a full-speed-ahead modus operandi looks to be a 2015 scenario at best.

The reason, in a word, is capacity. While CCAP will emerge sooner as a means of consolidating equipment in headends and lowering the costs of shifting QAM allocations as needs arise, it won’t be until operators begin implementing DOCSIS 3.1, EPoC or a combination of both that the network will be able to carry a full load of linear and on-demand IP TV simultaneously with legacy MPEG-2 channels, which is essential to making a transition that doesn’t require changing out all the legacy set-tops.

While speakers at a DOCSIS 3.1 symposium during Cable Tec Expo suggested equipment would come online as early as 2014 following CableLabs’ release of the specifications in early 2013, at least one vendor executive advised operators that’s not the case. Writing in a recent blog Mark Palazzo, vice president and general manager of Cisco System’s Cable Access Business Unit, commented, “Here’s how we anticipate the DOCSIS 3.1 timing to unfold: By early 2013, completion of the PHY (physical layer) and MAC (media access control) specs; silicon availability in 2014, and cable modem/CMTS availability in 2015.”

In other words, operators could be looking at allocating more capacity using DOCSIS 3.1 for their IP migrations just about the time EPoC becomes commercially available, which will pose some interesting strategic issues, to say the least. (For previous reporting on EPoC see December 2011, p. 8.)

In both cases, assuming current EPoC spec recommendations hold, the platforms will introduce a new modulation scheme, now widely used in wireless, known as OFDM (Orthogonal Frequency Division Multiplexing), in conjunction with a much higher order of modulation of up to 4096 QAM compared to today’s 256 QAM, resulting in the achievement of up to 10 Gbps of downstream capacity over 1 GHz of spectrum on the coax plant. Both platforms also contemplate using a more advanced form of forward error correction known as LPDC (Low Density Parity Check), which, according to SCTE CTO Daniel Howard, will improve noise immunity over DOCSIS 3.1 by several dB over current Reed-Solomon encoding at similar channel efficiency or provide greater channel efficiency at the same MER (modulation error rate).

DOCSIS 3.1, by opening a path to higher data capacity on the existing network analogous to what’s contemplated with EPoC, assures operators will have the option to get the most out of coax plant without moving off the DOCSIS platform. On the other hand, EPoC, at minimum, provides a way for operators to leverage EPON infrastructure to extend commercial-grade Ethernet services to customers via the coax links. More fundamentally, EPoC offers operators an opportunity to exploit the low costs and “dumb pipe” simplicity of an end-to-end Ethernet operating environment for all services while setting the stage for migration to all-fiber networks in the future.

This year CableLabs embraced engagement with EPoC at a deep level with plans to work on specifications for a key component, known as the Optical-Coax Unit (OCU), which will serve to perform the PHY-level translation between the digital optical EPON link and the coaxial RF medium while preserving a transparent path for the EPON MAC all the way to the customer premises. Without the OCU, EPoC would operate as a separate Ethernet link, taking the signal from the Optical Network Unit that terminates the optical EPON and regenerating it as an Ethernet transmission that mimics how the EPON link operates between the Optical Line Terminal (OLT) and ONU via components known as Coax Line Terminal (CLT) and Coax Network Unit (CNU).

With the OCU it becomes easier to dispense with use of AM optics by allowing EPON to transmit digitally to the HFC node and over RF to the home. For operators who envision capping DOCSIS and MPEG-2 for legacy services while using EPoC to simultaneously deliver an all-IP package, a key benefit of this mode of migration would be the savings that come with low-cost, easy-to-maintain digital optics.

But no matter which way operators go as these new platforms come online, there’s no easy path to IP migration, noted CableLabs CTO Ralph Brown. “We’re active in all the choices where we see promise.” Brown said. “The harder question is, how does any of it get deployed? In any capital-intensive area of technology discussion it’s easy to talk about point A and point B and the architecture at each. The hard part is knowing when and how to get from A to B in an optimal fashion. The real engineering is in the transition.”

One big hurdle operators face is the need to free up spectrum for higher throughput on the return path. While the participants in devising DOCSIS 3.1 have decided not to map out spectrum for return in the higher bands, they have yet to set the exact sub-band range for the return, which will be expanded to about 200 MHz, or about five times current capacity. “The biggest challenge for us will be moving the upstream split,” Brown said.

In addition to addressing the transition and upstream issues cited by Brown, operators will have to take steps to minimize signal interference and other barriers to implementing high levels of QAM, noted Daniel Howard. “We’ll need to tighten our networks further and eliminate ingress and impairments that can impact performance,” he said.

As for spectrum requirements Howard said there could be a need for more than 200 MHz on the upstream as well as a need for downstream expansion into levels beyond 1 GHz, since some of the current downstream spectrum will be consumed for the return. “To deliver our ultimate objective – 10Gbit/s downstream by 1Gbit/s upstream – we’ll need greater RF spectrum (1.2GHz to 1.5 GHz downstream, and 200MHz to 400 MHz upstream),” he said. “But this is far less than would have been required without the other improvements in signaling.”

Nor will it be as daunting to prepare networks to accommodate the highly sensitive 4096 QAM level downstream and possibly 1024 QAM or even 4096 upstream as it otherwise would be, thanks to the added robustness resulting from adoption of OFDM. Not only does OFDM result in greater bandwidth efficiency by virtue of allowing sub-carriers to be squeezed together, eliminating the need for guard bands between RF channels; it introduces longer symbol durations to the sub-carriers, making it “more capable of dealing with impulse and burst noise than are SC-QAM guard bands,” Howard said.

As Howard noted, operators don’t have to wait for rollout of 3.1-compliant gear to establish a more 3.1-like environment for transmitting data. There are ways to “efficiently stay ahead of consumer usage and demand,” he said. “Interim staging towards 3.1, like deploying 24×8 cable modems [a reference to 24-channel bonding in the downstream and eight-channel bonding upstream], will serve as stepping stones along the way.”

Indeed, said Jorge Salinger, Comcast vice president of access architecture, in an appearance at the Cable Tec Expo meeting, the MSO plans to deploy 3.1-based customer premises equipment before it actually implements the downstream capabilities, and it will wait even longer to implement the upstream. This is doable because 3.1 modems and other equipment are backward compatible with 3.0, and the cost difference between 3.1 and 3.0 modems will be significantly smaller than the 2.0-3.0 differential.

In a step industry officials hope will expedite deployment of 3.1 once it’s ready for prime time, SCTE announced formation of a special working group within the SCTE Standards Program that will develop best practices and requirements to prepare HFC networks for higher-capacity signaling schemes, including DOCSIS 3.1. “SCTE and CableLabs have a shared commitment to helping cable operators significantly accelerate deployment of advanced technologies such as DOCSIS 3.1,” said Joe Jensen, CTO of Buckeye CableSystem and chairman of the SCTE Engineering Committee. “By working closely to align training and best practices with technology development, we can ensure that new technologies are deployed as quickly as possible.”

Or, as Howard put it, the steps from specification adoption to learning how to use them can no longer be pursued serially over long periods of time. “We can’t take that time anymore,” he said.

Meanwhile, operators can begin exploiting some of the efficiencies harbingered by CCAP right away, thanks to the availability of new high density CCAP-compatible CMTSs (cable modem termination platforms) and universal edge QAM platforms. However, full-scale CCAP solutions won’t be available for testing until 2013, with large-scale deployments anticipated to begin in 2014 or 2015, depending on the vendor. Players moving in this direction include ARRIS, Casa Systems, Cisco Systems, CommScope, Harmonic and Motorola Mobility.

Motorola Mobility and Cisco Systems offered private showings of their still-unreleased CCAP platforms at Cable Tec Expo, but officials in both camps made clear they were a long way from delivering product. The important thing is to begin moving in the CCAP direction immediately by utilizing new high-density QAM line cards, said Cisco’s Mark Palazzo. “Keeping up with QAM expansion, and getting to CCAP, could be crazy expensive – if not carefully planned and executed,” Palazzo warned.

With Cisco’s cBR-8 fully integrated CCAP platform slated for rollout in 2014 now is the time to “start phasing,” which means “getting to a converged edge and then to CCAP,” he said. “Start by combining video and data QAMs. Do it this year.”

To that end Cisco earlier this year introduced the RF Gateway-10, a high-density universal edge QAM platform that can be populated with up to ten of the company’s new DS384 line cards. “Each 8-port card provides full-spectrum coverage, with 128 QAMs per port,” Palazzo said. “Fully loaded, meaning an RF GW-10 populated with 10 DS-384s, you’re at 160 Gbps.”

Such phase-one steps can reduce headend rack space requirements by 35 percent, he noted, adding: “Doing so doesn’t require ripping anything out – no forklift upgrades! – and sets operators on a path that makes CCAP attainable.”

ARRIS has gone even further in the phasing department with introduction of its E6000
Converged Edge Router, which will be available in Q1 as the successor to the C4 CMTS and as the launch pad for the vendor’s CCAP implementation. In the CCAP architecture this is the integrated CMTS that will interact with universal edge QAMs, where the ability to allocate and dynamically change any mix of DOCSIS and TV channels onto any QAM port will reside. The architecture can be implemented as a fully integrated unit or in a distributed mode with dispersed edge QAMs.

The new ARRIS CMTS won praise from Sam Chernak, senior vice president of access technology at Comcast Cable, one of five Tier 1 MSOs worldwide which ARRIS officials say are testing the new CMTS. “ARRIS has been a strong contributor to the development of next-generation access platforms such as CCAP, and we are excited to help them bring this to market,” Chernak said in a prepared statement. “They have been a technology partner for many years, and we look forward to continuing this with the CCAP platform.”

The first version of the E6000 will support up to 256 downstream channels per card, with seven cards filling a chassis for a capacity of 1,792 downstream channels. Upstream capacity is 96 channels per card for a total of 672 channels on the fully loaded chassis.

The E6000 weill leverage edge QAM features of the Media Services Platform (MSP) ARRIS acquired with purchase of BigBand Networks as the company moves to full CCAP implementation, said ARRIS CMO Stan Brovont. It’s an important stage setter for CCAP, he adds, but in truth the industry isn’t ready yet for CCAP.

“There’s still a big effort ahead for operators to get to the universal edge QAM,” Brovont said. “The operations conducted today out of standalone video and DOCSIS boxes aren’t organized to allow MSOs to operate the network out of a truly converged platform. Only a small handful are delivering DOCSIS and TV out of one QAM product.”

But that’s not to say there isn’t a huge focus on enabling migration to IP, which will be aided by use of media gateways such as ARRIS has developed to allow operators to stream both IP and MPEG-2 video to the home. “We’re big believers the migration will occur, which is why we’ve jumped in to offer a converged services client with our gateways,” Brovont said. “Once CCAP is implemented operators who have these gateways in place will be able to move video into IP on their QAM channels with a turn of the knob at the headend.”

While ARRIS is not touting the E6000 as a finished CCAP product, the platform does provide operators a CCAP-like ability to shift MPEG-2 TV channels that have been converted to IP over DOCSIS onto the dedicated DOCSIS QAMs, he noted. “We’re not yet supporting pure MPEG QAMs for broadcast video or VOD with version 1.0 of the E6000, but we are supporting traffic going from digital to DOCSIS,” he said.

Augmenting operators’ leverage to transfer TV content onto the DOCSIS streams are new channel bonding capabilities ARRIS introduced last month with version 8.1 of its C4 software in conjunction with gateways and modems that support 16- and 24-channel bonding. With the E6000 operators can implement aggressive expansion of broadband capacity and IP video delivery more readily, especially in big cities where space is limited, which will allow them to move their existing CMTSs elsewhere as new needs arise, Brovont noted.

“The higher density lowers the costs of adding DOCSIS channels in terms of operations, space and power consumption,” he said. “The fully filled E6000 draws 40 percent less power than any other CMTS. You stave off multimillion-dollar power increases just by deploying the E6000.”

Harmonic, with the most aggressive claims on the CCAP front, is touting its new NSG Pro universal edge platform as “the industry’s first true CCAP-compliant platform,” in the words of Nimrod Ben-Natan, the former head of Harmonic’s product marketing, solutions and strategy group who has been appointed to run the firm’s new edge and access business unit. “NSG Pro leverages Harmonic’s expertise in intelligent function integration to combine downstream services and an easy upgrade path to full CCAP – supporting DOCSIS 3.0 and beyond – in a unified CCAP chassis, enabling operators to redefine their cable architectures.”

While Harmonic has not yet completed development of the integrated CMTS component of a full CCAP solution and is not supporting integration of DOCSIS streams with MPEG at this point, the platform will readily accommodate the company’s implementation of DOCSIS with full CCAP functionality at some point in the future, officials said. Meanwhile, the extremely dense and modular platform, now in lab trials and due for general availability in Q1, will give operators the CCAP push-button functionalities required to dynamically allocate linear and narrowcast MPEG channels on each QAM port, said Asaf Matatyaou, director of cable edge and access solutions at Harmonic.

“The convergence of linear video and VOD on a single port on any QAM in any combination at high density eliminates splitting and combining,” Matatyaou said. “As a leading-edge QAM vendor we understand the requirements, and by offering this platform at such high density with CCAP compatibility we’ve created a future-proof path for operators to address their service needs while capping the volume of QAMs.”

When fully loaded, the nine-rack-unit NSG Pro chassis will support more than 10,000 QAMs, which “far exceeds the requirements of CCAP,” he noted. At the same time, the individual rack modules can be dispersed into different regional hub or local headend locations to facilitate local service configurations while operating as a unified whole from a management perspective.

While Harmonic has not produced CMTS gear in the past, the move to that side of the broadband supply chain is not a big stretch for the company, Matatyaou said. “We have a lot of experience integrating with DOCSIS and video back offices,” he commented. “So we’re leveraging that experience as well as multiple generations of edge QAM operations using our CableOS software.”

To complement the company’s CCAP initiative, Harmonic is also introducing a new family of compact forward-path transmitter modules featuring ultra-high-density optics as part of its SUPRALink and PWRLink product lines. The new transmitters deliver space savings, low power consumption and optimized fiber usage and network efficiency, Matatyaou said.

With all the emerging tools now at hand, operators can plan their next moves with greater clarity, implementing efficiencies now without having to worry about ending up on dead-end streets. But many will be conservative about how they spend their money in advance of full CCAP implementations.

Jeff Finkelstein, senior director for network architecture at Cox Communications, explained why his company can be counted in this camp. “Our facilities for serving from the edge to the customer are already packed very densely with the amount of equipment,” Finkelstein said. CCAP “is absolutely essential for our future growth as cable operators.”

But that doesn’t mean Cox needs to act before the standard is fully implemented. “For us we may decide that we want to move video service first, or we may decide we’re going to move data services first,” he said. “So it’s essential for the CCAP platforms of the future that they allow us to move whichever particular service we find most important at that time.”

With capacity on its existing modular CMTS platform that “we believe lasts us for years, we are going to be moving towards deploying CCAP in a later period of time,” he added. “We’re going to be taking a very methodical approach to rolling it out and hit those areas that are requiring the highest densities first and from there working it throughout our entire network.”