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Creating a broadband digital home

Posted: 01 Mar 2001 ?? ?Print Version ?Bookmark and Share

Keywords:broadband? digital home? pci? docsis? homepna?

The term "broadband digital home" tends to emphasize the comparatively simplistic idea of broadband Internet access. But a broader perspective is quickly evolving, one that takes into account the full spectrum of bundled services that can be delivered to the home over a broadband pipe. This includes not only Internet access but also local telephony, long-distance, cellular, paging and entertainment services, along with the necessary techniques for distributing these services throughout the home and ensuring its protection from unauthorized access.

Within this richer connectivity environment, cable and asymmetric digital subscriber line (adsl) modem technology must be evaluated on criteria that go beyond their ability to simply provide a fat pipe to the Internet. How widely available are the services that each technology supports? How and where do customers order services, how do they acquire the hardware and how is it installed? Finally, how well does hardware support all the various bundled broadband services that a consumer might want, both today and down the road, and how well can they be integrated into the multifunction broadband digital home?

Although ADSL uses the same subscriber loop as the telephone service, not all subscriber loops can reliably carry an ADSL signal. There is a trade-off of speed for distance and, as a result, a prospective customer's telephone line must first be qualified for ADSL service. And even after the line is qualified, it does not mean the challenges are over. Any number of problems can still surface that might require additional expensive truck rolls. Silicon solutions that focus only on power and density improvements will not solve the primary problems facing ADSL service deployment.

For cable, it is simply a case of whether the service is available in a particular area. Although cable services are widespread in Europe, much of the infrastructure is still not two-way-enabled. The consolidation of European multiservice operators (MSOs) has dramatically accelerated service deployment, but there remain ongoing battles over competing specifications. In addition to these factors, modem performance and the use of different service-dependent provisioning methods and protocols means that, at least today, hardware and services are inextricably linked. They must be decoupled before we see the necessary level of competition to reduce prices.

Once there is more uniformity across services, it will be possible to purchase broadband modems as easily and conveniently as dial-up V.90 models. However, standards are still evolving and deployment still requires an expensive service call by a technician to install and set up the modem. This can delay service initiation by several weeks. The ideal situation would be for modems to come already installed in the consumer's PC. In July, the first of just such a category of cable-modem products was certified by CableLabs. It uses Conexant's single-chip cable modem with a PCI interface. This configuration enables PC OEMs to attach their cable-modem products directly to the PC's internal PCI bus.

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. This flexibility enables 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, which is called the Docsis Version 1.0, will make the transition to a new standard, Docsis 1.1, over the next six to 12 months. Meanwhile, in Europe, there is still no well-defined and widely endorsed cable industry standard; however, both digital video broadcast (DVB) and EuroDocsis are well-established alternatives in this market.

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. As pioneered in Conexant's InfoSurge programmable single-chip cable modem, the software MAC architecture 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.

There are many ways to use the software MAC architecture so that proprietary enhancements can be added?either as new products roll out and need updates, or as standards evolve and differentiating features are required in the marketplace. For instance, by customizing the programmable MAC layer, vendors can implement their own unique technology while still retaining compliance with Docsis-Davic (Digital Audio Video Council)-DVB standards. The same is true for service providers that wish to support transport-type framing other than MPEG. Among them are high-level data link control or asynchronous transfer mode, both of which can be supported by alternative MAC architectures.

Rather than redesigning a chip to support such a new feature or specification and then waiting for a new silicon turn, the developer simply changes the MAC in the field. New MACs can be developed and tested with existing headends in the field, speeding up the time-to-market for a manufacturer wishing to address either new or developing specifications. A single IC with several software MAC implementations can be used to support multiple worldwide markets without the burden of unnecessary and unused hardware. In contrast, a full-hardware MAC must be either market-specific or force the manufacturer to pay for large amounts of unnecessary hardware, resulting in extra cost for the customer.

Completely 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 cable modem technology into set-top boxes and other Internet appliances. Other opportunities include voice-over-Internet protocol (VoIP) applications and host-based cable modems.

Modem support

For example, PCI, USB and VoIP implementations will need the cable modem device to support advanced Layer 2 and Layer 3 bridging/routing to destination ports and applications. Applications like 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 to 7 filtering. Video, voice and other types of traffic that require quality of service will necessitate the cable modem to receive, prioritize and forward traffic at line rate. A programmable broadband MAC is flexible and fast, so 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 makes this possible.

Although ADSL technology is not supported by the same degree of standards and certification processes as cable modems, this is quickly changing. Several efforts are under way, including those at the University of New Hampshire Interoperability Laboratory. More recently, the industrywide OpenDSL was launched; it is aimed at developing an open plug-and-play architecture for retail-grade customer premises equipment (CPE) interoperability and automated configuration to allow a CPE to be used on any DSL network.

Besides industry-standard service and provisioning for cable and ADSL modems, there are other differences to consider related to how these technologies are implemented in a home-networking environment. While there will always be applications for the broadband equivalent of a standalone V.90 or V.92 modem with a PCI or USB interface, users increasingly will want to share the greater bandwidth, or "pipe," between a home's multiple PCs or appliances and the network. The modem then becomes a "gateway" that routes and bridges video, data and voice content across various forms of home network, including phone-line networking (HomePNA), power-line networking (Home Plug) and wireless networking (Bluetooth technology or 802.11 short-range wireless connectivity). This capability opens the home to a broad array of new communication appliances and new services including telephony, interactive gaming and video on demand or home video servers and e-commerce terminals.

Developers of first- and second-generation home-networking products have focused so far on multifunction solutions that are centered around ADSL as the broadband component. For instance, the latest ADSL-based "four-in-one" solutions use horizontal integration across four different physical media to consolidate ADSL and other connectivity functionality into a single PCI slot, freeing slots for other PC applications. As an example, Conexant's AccessRunner chip set incorporates an ADSL transceiver that supports the 8Mbps full-rate ADSL or 1.5Mbps G.lite DSL standard, V.90 and V.92 dial-up modem technology and either HomePNA 1.0 (1Mbps) or HomePNA 2.0 (10Mbps) specifications. It is also Ethernet-ready to enable a high-speed LAN.

However, these early solutions face significant challenges, not the least of which is the dynamic still-evolving nature of the home-networking ecosystem. The only mature component in today's home-networking technology mix is Ethernet, which has been around for two decades. The other technologies are only a few years old and are still being defined, refined or both within the world's standards bodies. For instance, the HomePNA specification has undergone two generations of development in two years and the initial HomePlug standard has not yet been made final.

As for the broadband-access component, next-generation solutions cannot rely on a single technology. Cable, ADSL and other technologies are equally viable options that are undergoing their own standards evolution and they are heavily dependent on geographic availability. As networking and broadband options continue to evolve, designers are beginning to adopt a more modular home-networking strategy. This strategy revolves around the use of cost-optimized, high-performance home-networking processor solutions that provide the platform for easily connecting multiple digital devices in the home while sharing broadband Internet access among multiple PC users.

? Alberto Mantovani

Division Director, Small Business and Consumer Networking

Conexant Systems Inc.

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