Programmable Cable Modems Get a Boost

Electronic News, Oct 23, 2000 by Brett Bernath

THE DIGITAL CABLE MODEM has emerged as one of the most promising product platforms in the broadband connectivity arena. As this new market quickly takes shape, it has become increasingly clear that cable modem manufacturers will require significant levels of system integration and flexibility in order to navigate a rapidly changing landscape characterized by multiple, evolving standards, ever-changing feature requirements and growing cost-pressures. The ease with which OEMs can navigate this landscape increasingly depends on the semiconductor system architecture that they choose.

As cable-modem standards, market requirements and technologies evolve, one of the biggest challenges is in the design of the broadband media access control (MAC) layer. Programmable cable MAC architectures provide a significantly more flexible alternative to full-hardware MAC solutions as designers cope with these changing dynamics. The flexibility of the programmable architecture will enable manufacturers to support multiple worldwide broadband standards while providing a cost-effective migration path to new standards, new feature sets and improved system performance.

The standards environment is particularly dynamic. The current cable industry standard in the United States, the data over cable service interface specification (DOCSIS) Version 1.0, will be transitioned to a new standard, DOCSIS 1.1, over the next six to 12 months. Currently, there is not a cable industry standard in Europe; however, both digital video broadcast (DVB) and EuroDOCSIS are well-established alternatives in this market.

The Programmable

MAC Factor

The programmable broadband MAC architecture enables designers to navigate this changing standards environment. With sufficiently high levels of system integration, this architecture also enables designers to accommodate changing requirements in feature sets and product performance. Vendors can implement their own unique technology by customizing the programmable MAC layer while still retaining compliance with DOCSIS/DAVIC/DVB standards. The same is true for service providers who wish to support transport-type framing other than MPEG. Examples include highlevel data link control or asynchronous transfer mode, both of which can be supported by alternative MAC architectures. A programmable MAC architecture offers a migration path to this kind of technology.

New product configurations can also be supported by the programmable MAC architecture. As standards converge and encompass voice, data and new-media applications, there is the opportunity to integrate cablemodem technology into set-top boxes and other Internet appliances. There are also other opportunities such as voice-over-Internet Protocol (VoIP) applications, and host-based cable modems.

For example, PCI, USB, and VoIP implementations will require the cable-modem device to support advanced Layer 2 and Layer 3 bridging/routing to a variety of destination ports and applications. Applications such as games or Web browsers could also be executed on the cable modem acting as a network computer, but this will require application-dependent Layer 4-7 filtering. Video, voice and other types of traffic that require quality of service will necessitate that the cable modem receive, prioritize, and forward traffic at line rate. Because a programmable broadband MAC is flexible and fast, it is possible to support new requirements and applications as they evolve, without unduly burdening the embedded processor and limiting system performance.

Finally, the programmable MAC architecture also helps designers serve worldwide markets with a single platform. More and more cable modem suppliers must simultaneously support evolving U.S. DOCSIS standards as well as the DVB,DAVIC, and the more extensive Euromodem specification established by the European Cable Communications Association, the parent organization for the EuroCableLabs industry standards group. A programmable MAC architecture is designed to support these and future standards within a single IC.

Hard-wired architectures force several undesirable elements upon manufacturers, including slower time-to-market, increased system costs, and an inherent lack of flexibility. A programmable MAC architecture solves each of these problems.

Fundamentally, a programmable MAC implementation consists of a processor, memory, and various hardware coprocessors used to both process the data and move it through the system. The system is partitioned so that hardware performs computationally intensive operations on data, while moving the data through the system. The MAC software handles the control functions, manages the data flow, and executes any other functions that might change in the future. Even though embedded processor performance has improved, companies have customized the MAC processor to optimize data flow through the cable modem and to eliminate wasted processor bandwidth.

Performance and flexibility are the key benefits of a programmable broadband MAC. From a flexibility standpoint, this approach allows software upgrades to be made via simple network downloads from the head-end. MAC updates can be posted on a Web site and the cable companies can download them to their customers. As for speed improvements, not only does this approach offer better overall system performance, it also offers the opportunity for proprietary enhancements to be delivered as new products roll out and need updates, or as standards evolve and differentiating features are required in the marketplace.