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April 26, 1999

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DSL Comes Together

The Universal Asymmetric Digital Subscriber Line standard for consumer DSL will galvanize the market and speed deployment. At the same time, value-added services are trickling into the marketplace.

By Jason Levitt

Related links:

sidebar story: Compaq Pushes DSL Hardware And Software

InternetView: Universal ADSL Slow To Start

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PDF file: Emerging DSL Standards and Universal ADSL And Its Competitors
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sense of urgency was in the air at the recent DSLcon in Dallas. With nearly every major player in the digital subscriber line industry present, one might expect nascent rivalry, but the overwhelming feeling was one of unity. DSL deployment, standards, and testing clearly aren't moving as fast as everyone would like--and, for the moment, all anyone wants is for those things to progress as quickly as possible. Meanwhile, some competitive broadband services are moving forward with aplomb. "Let's not kid ourselves. The cable industry, with all of their problems--their truck rolls, their security issues--is killing us," says Nigel Cole, VP for new business development at Orckit Communications Ltd., a leading supplier of DSL equipment. Depending on how you count them, year-end 1998 totals for DSL nationwide were about 39,000 ports, as opposed to 500,000 for cable modems--though DSL deployment expanded threefold by the end of the first quarter of 1999. Though it's likely that the majority of the cable-modem circuits are used by consumers, it's nearly impossible to tell how many businesses might be using cable modems, especially as a conduit for virtual private networks back to a corporate LAN. Few cable-modem vendors are supplying business-class service yet, though, and it's unclear how they will resolve business issues such as guaranteed bandwidth and security, which arise because of cable-modem architecture.

As many as 500 cable-modem users may share the same network, giving other users potential "sniffing" access to your packets and exported disk volumes, and causing throughput to drop when other users on your network segment hog the pipe. In contrast, DSL, a familiar point-to-point topology, doesn't suffer from these problems, but comes with its own set of issues. There are at least 10 variants of DSL in use, some proprietary, and some standardized by organizations such as the International Telecommunications Union.

Three variants seem to be emerging from the pack, not as the current front-runners, but as the ones most likely to succeed. For business-class service, the faster symmetric variants of HDSL2 and SDSL, which don't allow simultaneous voice access, are favored, while on the low end, Universal ADSL is poised to create an entry-level price point for DSL that is expected to galvanize the market for high-bandwidth, value-added services.

UADSL, also called "G.lite" and "G.992.2" (the standard's actual reference number), was still emergingwhen I last wrote at length about DSL ("Waiting for DSL," Oct. 5, 1998). A draft standard is now in place, but it's still not a formal standard--final ratification is expected in June.

Meanwhile, PC manufacturers and DSL equipment vendors are starting to test their preliminary UADSL offerings (see sidebar story, "Compaq Pushes DSL Hardware And Software"). The first major public interoperability testing of UADSL equipment will occur at the Supercomm show in Atlanta in June.

In the real world, Fujitsu, GTE, Intel and Orckit recently completed a small, 50-home test deployment of DSL with specifications similar to UADSL. They were able to achieve full-rate speed--512 Kbps upstream and 1,536 Kbps downstream--at 15,000 feet, as well as reduced speed at longer distances (in thiscase, the maximum upstream speed was faster than the UADSL maximum of 384 Kbps), with simultaneous use of the line for voice service.

Interestingly, customer-premises problems were almost exclusively due to telephone handsets, which tests found had wide-ranging impedance changes and ring trips that generated DC pulses into the DSL modem equipment. The result was that when telephone handsets were off-hook, throughput went down, and when phone ringing occurred, service was disrupted momentarily.