Comcast’s CMAP Gains As Cable TV-to-IP Migration Path

Bruce McClelland, president, broadband communications systems, ARRIS

Bruce McClelland, president, broadband communications systems, ARRIS

May 25, 2010 – With mounting pressure from senior cable management for a cost-effective IP migration solution, the engineering community is rapidly rallying around the Comcast next generation network architecture and its key enabling component, the Converged Multi-Access Platform.

ARRIS in early May underscored the developmental force being generated by this consensus with demonstration of an end-to-end architecture which, while not a product, offered strong evidence as to the direction the industry is going as operators seek to reduce the costs and speed the pace of IP migration. “This isn’t just about showing an interpretation of technical specifications,” said Bruce McClelland, president of broadband communications systems at ARRIS. “People are talking about putting this architecture into operation within the next 12 months.”

While many details remain to be worked out, the core hardware design is well enough understood to allow chipmakers to proceed with development of CMAP-compliant devices, said Todd Kessler, vice president of product line management for the network technologies division at ARRIS. “In some cases silicon vendors are already a good way down the path,” Kessler said.

The built-in software or firmware aspects of the CMAP functionalities in these programmable chips can be adjusted as further details are worked out and standards emerge, assuming the architecture becomes woven into the specifications-setting process at CableLabs. “The architecture has the endorsement of the major players and others are starting to get involved,” Kessler said.

But some MSOs will not wait for finalization of standards, much as the early adopters in DOCSIS 3.0 deployments preceded spec approvals, he added. “They want a standards-compliant solution, but they feel pressure to move forward sooner than later,” he said.

As described by Comcast officials Jorge Salinger, vice president of access architecture, and John Leddy, senior vice president of converged services, in a recent article written for CT Magazine, the CMAP is the key component in the NGAA (Next Generation Access Architecture) the company is spearheading with wide input from technology experts and chip manufacturers. The CMAP, a distributed edge device, is an extremely high-density advanced processing platform that combines the functionalities of the DOCSIS 3.0 CMTS (Cable Modem Termination System) and all broadcast and unicast QAMs (quadrature amplitude modulators) with great flexibility to alter how much bandwidth is allocated to traditional MPEG-2 transport versus DOCSIS-based IP transport. In so doing it eliminates what would otherwise be a rapidly escalating stack of components dedicated to various service categories with rigid dividing lines between the resources allocated to MPEG-2 and IP transport.

Along with flexibility to shift the proportions of MPEG-2 and IP content over time without any adjustments in hardware, the CMAP allows operators to configure service groups on a per-service basis – for example, a video-on-demand service group or HD broadcast service group – versus today’s homogeneous approach to service group configuration across all services. Unicast QAMs can be configured on a per-port basis while preserving the uniform configuration of all broadcast QAMs across all ports served by a downstream line card.

Many other efficiencies are encompassed in the CMAP design, including support for simultaneous delivery of the two proprietary encryption systems used in North American cable without requiring special-purpose hardware. The Comcast officials reported that some chip vendors are developing high-density QAM chips with the ability to support all channels on a single chip. Because the CMAP design relies on direct digital synthesis techniques that can be accommodated on existing field programmable gateway arrays (FPGAs), the industry will not have to await fabrication of new silicon to proceed with development of CMAP chips, they said.

Along with CMAP other important core components of Comcast’s NGAA include the downstream monitor (DMON), a device that interoperates with vendor software systems to provide a new level of network monitoring, maintenance and operations functions; the next-generation operations manager (NGOM), which is designed to leverage existing and new field handheld equipment to streamline execution of many basic tech operations processes, and the high-spectrum gateway (HSG), which supports operations over spectrum above today’s 1 GHz cutoff point.
HSG employs solutions such as Ethernet over glass, new types of RF transmission gear and higher order modulation such as OFDM (Orthogonal Frequency Division Multiplexing) and 4048 QAM. Salinger and Leddy said this new path will deliver spectral efficiencies approaching 10 bits per Hertz, or close to 60 megabits-per-second per 6 MHz RF channel, as compared to the 38 mbps channels commonly in use today.
From a premises gateway perspective, as demonstrated by ARRIS, the CMAP architecture allows operators to leverage the mutli-device service efficiencies of IP on a migration path that gives them the flexibility to displace legacy MPEG-2 hardware at whatever pace they choose. “We believe the mass legacy base of set-tops isn’t going away tomorrow,” McClelland said. “There’s an opportunity for transition technologies to allow operators to migrate to more IP-centric video services. The ARRIS Whole Home Solution is our example of how you can manage that migration to fit your needs.”

McClelland said the Whole Home Solution will include a family of gateway and media player products supporting hybrid and full IP architectures. These gateways and players will combine simultaneous use of feature-rich video and telephony services, multi-room DVR, Wi-Fi, DOCSIS 3.0 data rates and other services, he said. Operators can configure multi-room subscriber access to unicast and multicast content from multiple sources, including over-the-top and personal media as well as subscription cable.

In the model displayed by ARRIS at The Cable Show, the gateway represented an aggressive approach to implementing IP, such as might be done with a new subscriber or transfer of an existing subscriber to a higher tier of whole-home integrated IP service. Here all incoming MPEG-2 transport signals are translated to IP, making for a uniform IP-based service integration within the home and eliminating the need for traditional set-tops.

The gateway is compatible with the proprietary encryption systems used for MPEG-2 TV, allowing it to perform decryption and then to send signals securely to TVs and other devices using the DTCP-IP (Digital Transmission Content Protection) security that has been endorsed by CableLabs for home distribution of IP signals as part of the DLNA (Digital Living Network Alliance) home networking standard. All the IP distribution would take place over MoCA, Cat 5 Ethernet wiring or high-speed wireless.

Newer model IP-connected types of TVs could be served directly with tuning support from the gateway, while older models would require a low-cost IP translator. All DVR and tuning functionalities would be served by the gateway, which in this case had six tuners on board.

Some operators might want the legacy digital TV transcoded from MPEG-2 to MPEG-4, which could be accommodated in the gateway, while others would prefer to avoid the expense of the transcoding mechanism by sending the signals via IP while retaining the MPEG-2 compression, McClelland noted. At the same time, IP video and other traffic sent from the CMAP over the bonded DOCSIS 3.0 channels would be distributed directly to the intended devices in whatever streaming/compression format they originated in. “Support for Microsoft Silverlight, Flash and other formats will be built into these gateways,” McClelland said.

CMAP architecture allows operators to migrate to IP at whatever pace suits them. Some will replicate all their TV services in IP using the added bandwidth made possible by the NGAA’s HSG component to support simulcast in new and legacy modes, much as many operators have done in the analog-to-digital transition. Comcast, by eliminating most of its analog bandwidth through use of DTAs (digital terminal adapters) that translate digital signals to analog for analog households, has freed up a lot of bandwidth that could be used in conjunction with the HSG to support IP-MPEG simulcast.

Other operators will take a less aggressive path to IP, choosing instead to offer ever more unicast time-shifted content in that mode over DOCSIS 3.0 while relying on CMAP flexibility to gradually increase the proportion of bandwidth devoted to IP. Whatever the pace of migration, all operators will have multiple options such as ARRIS proposes to support different approaches to signal distribution in the home, depending on whether a particular household is using legacy set-tops or is suited to the greenfield all-IP approach.

The growing industry embrace of the CMAP architecture appears to have sidetracked much of the early interest in so-called DOCSIS 3.0 bypass or DOCSIS Lite options, where the costs of supporting huge IP video flows through ever more CMTS blades were to be avoided by layering DOCSIS media access control functionalities onto IP streams at the network edge. The combination of ever higher density efficiencies on CMTS blades with the QAM efficiencies made possible by super-dense chips designed for CMAP has opened a transition path to IP video via DOCSIS 3.0 that can begin with use of current generation CMTSs and move to CMAP devices without requiring a move to bypass, McClelland noted.

“We think creating a bypass standard and solving all the interoperability issues that go with that would be a lot of work and ultimately not helpful to the long-term evolution to IP,” he said.