[Maximizing Copper Pipes -PCWeek Test]
Date: Wednesday, March 12, 1997
Source: PC Week
PC Week via Individual Inc. : The current state of high-speed remote access is filled with possibilities, if not products. To determine whether DMT (Discreet Multi-Tone) ADSL (asynchronous digital subscriber line) technology is indeed the most promising alternative for high-speed remote Internet or corporate intranet access, PC Week Labs scrutinized Amati Communications Corp.'s Overture 8 DMT ADSL modems--still in limited release for
field trials--and found them a snap to set up. There is no software to install. In fact, there is no user interface nor configuration options for the end user
at all, so theoretically, little can go wrong. The Overture 8 DMT ADSL modems are a matched pair of devices: the ATU-R subscriber modem and the ATU-C central office modem. The biggest distinction between the units is that the ATU-C includes two more RJ-45 ports to accommodate consoles for ADSL and router management. The Overture 8 DMT ADSL modem pair was simple to set up. Though it was both unsettling and refreshing to use a product that has no user interface, we found that it worked as advertised without tinkering. We simply plugged in the units--factory preconfigured to produce 4M-bps throughput downstream and 384K bps upstream--and they worked, allowing a computer at each end of our ADSL link to see the other. It took a moment for both units to synchronize, indicated by one of the three lights in the front of the units. DMT is a method of frequency division designed to train, or synchronize, at the fastest speed possible to provide the greatest performance, especially under adverse or noisy line conditions.
The upstream, downstream and plain-old telephone service channels operate on separate frequencies so that service providers can keep voice and data on separate networks, which eases the transfer of data to either circuit or cell-switched connections at the central office. We connected the supplied RS-232-to-RJ-11 cable to the ADSL management port on our prerelease ATU-C central office modem, but the interface is limited to two-digit alphanumeric commands that generate coded hexadecimal responses about polling parameters, the status of various packet frames and other debugging information. Intelligible software for the router interface is still under development. Our test configuration consisted of two Pentium systems running Windows NT 4.0, each connected over Ethernet to its Overture 8 modem. We simulated the copper loop by interconnecting the line port on both modems with a standard RJ-11 patch cable. Using Windows Explorer, we transferred files in both directions. Our downstream transfer rate was seven
times the upstream rate. Using Microsoft Corp.'s Internet Explorer, we browsed the Web server running on each NT 4.0 server. The static pages we viewed responded with no discernible delay in either direction, but keep in mind that our copper loop was very short, and both line noise and length affect ADSL performance. A 10,000-foot loop will provide better throughput than an 18,000-foot loop, the maximum length allowed by the technology at this point. Because telcos certainly can't justify earmarking a DMT ADSL modem for each and every customer who uses one at their end, a scaling device is needed. In conjunction with the Overture 8 DMT ADSL modem pair, Amati's recently released Allegro Access Concentrator supplies the missing piece in the end-to-end solution that telcos need. The Allegro allows telcos to aggregate ADSL signals into, say, an ATM cell-based or frame relay network. A new release of the revamped Overture 8 DMT ADSL modem pair is scheduled for April 1. Pricing has not been set. Amati, of San Jose, Calif., can be reached at (408) 879-2000 or www.amati.com. Amati's Overture 8 DMT/ADSL modems
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