[Product Innovation]
Host-Based ADSL Modem Halves Power And Cost
A software-based architecture allows the two-chip set to support multiple standards at the full ADSL rate.
The demand for inexpensive high-speed Internet access anytime and anywhere is accelerating, putting the onus upon notebook and laptop manufacturers to respond in kind. Service ubiquity and low costs have made V.90 modems, either as PC Cards or as fully embedded components, the solution of choice to date. But the recent surge in xDSL deployment has altered the service landscape. High-speed access, at theoretical rates of up to 8 Mbits/s, is now available almost everywhere.
This has been good news for manufacturers of traditional xDSL chip sets, which use a DSP from the likes of Lucent or Analog Devices at their core. These devices have cornered much of the desktop market, but the market dynamics are changing. Lower power for portability and lower cost for entry have been the rallying cries of the masses as they truck their laptops from home to work, or across state lines or country borders. Increased travel, with the availability of myriad xDSL service levels and standards such as G.dmt or G.lite, necessitates flexibility and on-the-fly adaptability.
These requirements motivated Integrated Telecom Express (ITeX) Inc. of Santa Clara, Calif., to introduce the first full-speed, ADSL chip set with a host-based architecture. This development promises to cut the cost and power requirements of a DSL implementation in half. Dubbed the Scalable ADSL Modem (SAM), it employs the unused cycles of a system's host CPU to perform much of the ADSL processing. Doing so reduces the required gate count to get ADSL into a PC by a factor of five, leading to the lower power and cost. At the same time, the architecture gives the chip set the flexibility to support multiple standards—including ITU G.dmt, ANSI T1.413, and ITU G.lite—at up to 8 Mbits/s downstream and 768 Mbits/s upstream. Also, any changes in the ADSL standards can be addressed in the field with a software download.
Targeting PCs, notebooks, PDAs, and Internet appliances, the chip set is one of many new peripherals that depend on the host CPU for processing power. That's not surprising, though. All of these peripherals are based on the premise that CPU power is growing faster than the demands of the applications being run on the average PC, currently represented by a 500-MHz Pentium III. With the availability of systems in excess of 1 GHz, the sweetspot will be advancing rapidly.
Consequently, there is plenty of room for new introductions, which include MPEG decoders for digital TV, encryption, and high-speed modems. The latest Intel Developers Forum only underscored this trend, as Intel indicated how the power of its CPUs at 1 GHz and above will be increasingly directed toward software implementations of peripherals. In turn, this should reduce the cost of high-speed Internet access.
Of course, using unused CPU clock cycles can have its disadvantages. When the system gets bogged down with advanced applications, service could possibly be lowered or interrupted. With the SAM, this is unlikely. Generally, the host CPU is relatively idle during most Internet transfers. For example, the SAM uses only 46% of a 500-MHz P-III processor to achieve 8-Mbit/s speed. The remaining 54% is ample enough for any other applications.
One of the SAM's key assets is its scalability. Processor use can be lowered to 35% to achieve the 6-Mbit/s rate, which is the fastest rate commonly available. Yet the standard ADSL service is 384 kbits/s downstream and 128 kbits/s upstream, requiring only 6% of a 500-MHz CPU's bandwidth. During idle-line periods, a patent-pending CPU cutback feature senses that there is no active data and lowers processor use to as low as 16% on an 8-Mbit/s line.
The combination of CPU cutback and the patent-granted auto-configuration make the SAM particularly attractive to notebook and laptop manufacturers. The former reduces power consumption, while the latter lets customers plug their system into any ADSL jack without knowing the central-office standard in use—anywhere in the world.
Reprints
