Paradyne Hotwire MVL Allowed To Register Under FCC Part 68

By: John Spofford

Digital subscriber line (DSL) vendor Paradyne Corp. offers the HotWire Multiple Virtual Line (MVL), a proprietary system of customer premises endpoints and a carrier-based concentrator targeted at the business market. An major advantage claimed by the Largo, FL-based company is that MVL technology, a variant of DSL, does not interfere with other services such as T-1 data lines or with plain old telephone service (POTS). Paradyne set out to prove its claim with the help of the FCC.

The FCC this week granted Paradyne the authority to register the Hotwire MVL customer premises equipment under part 68 of the "FCC Rules for the Registration of Telephone Equipment" code. The Hotwire MVL system is the first and, to date, the only DSL product granted approval to register as Part 68 compliant, essentially certifying the equipment safe to deploy in the telephone network without harming the public switched telephone network.

Strategic move for Paradyne
Part 68 approval may be more of a strategic move than a technical achievement for Paradyne. While the Part 68 FCC rules establish mandatory technical requirements that protect the telephone network, Part 68 actually does not address DSL equipment. On this surface this makes Part 68 certification a bit of a hollow boast, however because of the rapid growth of Internet data access services, it is expected that the rules eventually will be revised to permit the registration of DSL equipment.

Rather than waiting on the bureaucrats, Paradyne proactively petitioned the FCC for a waiver of select out-of-band signal power rules (Section 68.308e) originally intended to register analog voiceband equipment. Paradyne engineers proposed an alternative technical specification to guide the FCC in determining Hotwire MVL's accordance with Part 68, which the FCC accepted in the waiver.

Legal protection for carriers?
While the "Part 68 approved" has the ring of an advertising slogan, the certification gives Paradyne a possible selling point as it signs up carrier customers—less legal liability.

"Other DSL technologies have more intrusive [power spectral density] masks and, potentially, may not qualify for Part 68 approval, increasing the liability of those service providers who deploy them," says John Freeman, principal analyst of networking strategies at Current Analysis, a Sterling VA-based consultancy.

The Telecommunications Act of 1996 opened phone networks to competitive local exchange carriers (CLECs) who in turn can colocate equipment in telephone central offices or lease copper loops to provide services that compete with the incumbent the local exchange carriers (LEC). While the intention of the act was to spur competition in the telecommunications market, it has been most successful in setting off a legal firestorm that burns to this day.

"Lawyers, legislators, and lobbyists are just now beginning to prepare for future legal battles revolving around the inter-pair service disruption that is bound to occur as multiple CLECs, as well as the incumbent LEC, deploy large numbers and multiple versions of DSL in each [telephone cable] binder group. By using a Part 68-approved technology such as MVL, [the carriers] can, to a large extent, protect themselves against such legal action when DSL deployment hits mass market scale in the next couple of years," Freeman suggests.

The Nuts and Bolts of MVL
MVL is a proprietary DSL technology currently incompatible with existing asymmetrical DSL modems, including the so-called G-Lite modems developed for the residential data market. Created instead with an eye for small office applications, Paradyne designed a new type of DSL modem from the ground up. It does not use discrete multitone (DMT) or carrierless amplitude/phase (CAP) line code, but it is designed to be spectrally-friendly with CAP or DMT ADSL.

MVL is also compatible with legacy services such as POTS, basic rate ISDN, T-1, or the European E-1. The technology was designed to meet the same power spectral density mask and total signal power constraints as those specified under the mature, industry specification T1.601 for ISDN BRI equipment.

Paradyne claims that MVL is virtually immune to line interference and will not interfere with other coexisting services in the same binder group. It accomplishes this by limiting the use of higher frequencies to the lower 10% of those used by full-rate (up to 7 Mbps) ADSL, and transmitting at a power level typically one sixteenth that of DMT chipsets. Despite this low power level MVL reportedly will work reliably up to 24,000 ft over 24 gauge AWG wire.

Low power a plus
The low-power design lowers heat output—an important consideration in both telco central offices and remote office applications. Less heat and power consumption also allows Paradyne to increase port density—as many as 2,000 MVL ports could be provisioned in a standard seven-foot equipment rack.

However, the use of lower frequencies also reduces the available bandwidth. MVL is capable of 768 Kbps either upstream or downstream, although not both at once. The system features dynamic rate adaptation that allows modems to be configured in increments of 64 Kbps at speeds ranging from 128 Kbps to 768 Kbps.

Interestingly, if configured as a symmetric modem, the formula provides a two-way 384 Kbps service, a bandwidth sweet spot favored for videoconferencing applications.

Despite its benefits, MVL still faces an uphill fight against the "DSL-lite consortium" in which many DSL vendors, including Paradyne, have participated. A clear concern that remains is how compatible MVL will prove to be with DMT, the line code expected to carry DSL technology into the residential mainstream.