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October 5, 1998

Waiting For DSL

Digital subscriber line technology may be the best choice yet for high-speed Internet access. Carriers are scrambling to provide the service, which is largely unavailable and costly.

By Jason Levitt

he grumbling in the comp.dcom.xdsl newsgroup is getting louder. It seems that for every new digital subscriber line user who can't believe he or she has obtained 1-Mbps Internet access from a home office, there are two others who are dying to tell you their latest horror stories involving some clueless administrative flunky representing a major CLEC (competitive local exchange carrier) or local carrier who can't, or won't, get them DSL hookups. Let's just say that the entire DSL industry is a bit stressed right now--and with good reason.

DSL is widely perceived as the best bet in the United States for consumer, mass-market, high-speed Internet access, and it's expected to drive a new wave of applications in both the business and consumer markets. In the business arena, DSL is the clear choice for home-office workers and telecommuters who want their home desktops connected at LAN speeds, as well as for companies seeking a virtual private network for extranet applications. To sweeten the deal, software and hardware vendors agree that DSL is the wave of the future. With Bill Gates publicly cooing over the prospect of the forthcoming DSL G.lite standard, and numerous vendors shipping or planning to ship DSL CPE (customer-premises equipment), DSL's future seems assured.

And yet, many areas of the United States are still waiting for deployment of DSL. Also, the technology lacks a standard that will drive a new commodity market for DSL equipment. For business customers, it's eerily similar to 1994, when ISDN rollouts didn't happen nearly as fast as news releases would have you believe. DSL, like ISDN at that time, lacks the standards and interoperability testing that will give businesses and consumers a variety of inexpensive choices for both client and server hardware.

The DSL newsgroup noise, which would also ring a bell with those early ISDN customers, is symptomatic of the industry's relative inexperience with DSL technology, but it's also the result of corporate posturing and overpromising designed to generate a feeling of well-being among customers and stockholders.

"No one is making money on DSL right now," says Glenn Ward, VP of broadband development for Bell Canada, referring mainly to the CLECs and ILECs (incumbent local exchange carriers) that are scrambling to build a DSL infrastructure. "They're in this for market share and experience." Ward echoes the general sentiment that DSL won't become profitable and widely accepted until the G.lite standard is in place. This standard is expected to shift the cost of the CPE--meaning the DSL modem--to the consumer and eliminate the "truck roll," or the need for skilled technicians to visit each DSL customer site. Currently, a technician must split the connection into separate voice and data wire segments using low-pass filters that separate the voice frequencies, at 400 Hz to 4,000 Hz, from the higher-rate data frequencies.

Road To G.lite
Just as the ISDN market was jump-started by the NI-1 standard and interoperability testing that created a standards-based market for ISDN equipment in the United States, customers and vendors alike are anxiously awaiting a standard for DSL equipment interoperability. That standard, dubbed G.lite but also called variously Consumer Asymmetrical DSL (ADSL)--not to be confused with Rockwell International Corp.'s defunct QAM-based Consumer DSL chipset unveiled last fall--or Universal ADSL, is being developed by the Universal ADSL Working Group (www.uawg.org), an advisory group comprising nearly all the major DSL equipment manufacturers. The initial proposal, Working Document 1.0, was announced at the Supercomm trade show in Atlanta in June. On Oct. 23, the preliminary G.lite standard will be put to a vote by the UAWG and is then expected to be passed on as a recommendation to the International Telecommunication Union. The ITU is expected to ratify an official standard for G.lite by the end of the year.

Some details of the future G.lite standard are clear, and CPE based on it may appear as early as December. The G.lite standard, which is ADSL, will be based on the ANSI standard T1.413 Issue 2 DMT Line Code and has targeted 1.5 Mbps downstream and 384 Kbps upstream as its maximum speeds. "Rate-adaptive" fractional amounts less than those maximums also are part of the standard, so an ISP could offer 256 Kbps symmetric as a G.lite connection speed. However, to simplify equipment and provisioning requirements, equipment will be limited to those maximum speeds.

The 1.5-Mbps/384-Kbps speed limitation may seem restrictive compared with DSL's typically advertised maximum downstream speed of 7 Mbps, but it is based on empirical testing of typical customer wiring scenarios and on the overall bandwidth available through Internet service providers.

DSL lines require quality copper loops--that means no load coils, no more than 2,500 feet between bridge taps, and, generally, a (driving) distance of 18,000 feet or less from the central office. At higher speeds, distance requirements become more critical and lines are more easily disrupted by "disturbers," such as ISDN and T1 lines in the same wire bundles as the DSL lines.

Although G.lite is being promoted as a "splitterless" standard, the engineering realities of new standards and new silicon mean that, initially, there likely will still be some need for splitters, filters, and even new customer-premises wiring. As the G.lite standard matures with a better understanding of the issues, as well as better vendor chip implementations, it probably will become closer to being truly splitterless.

Of course, even at G.lite speeds, the UARTs (Universal Asynchronous Receiver/Transmitters) on conventional PC serial ports will be unable to keep up. Thus, external, single-user PC modems that use serial technology will employ Universal Serial Bus ports on PCs or, possibly, enhanced parallel ports.

Router and bridge units, the only DSL modems available, use Ethernet. Newer chipsets, such as Rockwell's recently announced V.90/ADSL combo chipset, combine the G.lite and V.90 standards in one modem, offering customers a choice of connection profiles.