Microsoft Dials Into ADSL Interoperability - an asymmetrical digital subscriber line interoperability standard - Company Business and Marketing

As ISDN begins to show the telltale signs of aging, Microsoft has announced a collaboration with other high-profile vendors to develop an asymmetrical digital subscriber line (ADSL) interoperability model that is designed to advance broadband service interoperability. Microsoft and partners, Alcatel (Paris), Cisco Systems Inc. (San Jose, Calif.), Fore Systems Inc. (Warrendale, Pa.), U.S. Robotics (Skokie, Ill.) and Westell Technologies Inc. (Aurora, Ill.) are working together to define an architecture for point-to-point protocol (PPP) over asynchronous transfer mode (ATM) over ADSL. With this approach, the collaborators hope to have the architecture adopted by the standards bodies and to speed ADSL deployment.

In addition to providing an efficient path for migrating legacy applications into ADSL, the PPP over ATM over ADSL model offers other features. The use of ATM is an appropriate way to do messaging over ADSL because both technologies are compatible. Additionally, the ATM over ADSL architecture preserves the high-speed characteristics and quality of service guarantees without changing protocols. The proposed model also supports delivering, over ATM, operational features that are established in PPP, such as authentication, encryption, layer 3 address auto-configuration, and layer 3 transparency.

Despite the reasonableness of this approach, John Girard, research director of Gartner Group's Network Center (Stamford, Conn.), believes that there are more pressing issues that must be worked out: "The biggest issue of all has nothing to do with the points addressed in the Microsoft collaboration." Girard believes the critical factor in ADSL adoption is to assure that high-speed DSL can run on unconditioned copper lines. If the user has to condition the line, the user must incur high costs, which is reminiscent of ISDN deployment. Girard has not seen substantial evidence indicating tat these performance issues have been resolved for DSL, particularly in long runs -- for example, 2 miles -- from the central office.

In addition, to these performance issues, another difficult issue awaiting resolution is whether Carrierless Amplitude and Phase Modulation or Discrete Multitone line code should be the standard. Girard also believes that the communications industry needs to determine if the ADSL service should be a full telco bypass service or whether it should be selective bypass.

Despite these technical difficulties, Microsoft's participation in the collaboration may be enough to provide some indirect benefits to speed ADSL deployment. Its endorsement may help remove the inertia among ISVs and also help free up venture capital, which can be used to overcome the technical challenges delaying the broad-band service deployment.

Although this initiative provides no inherent advantage for Windows NT users, if Microsoft adopts this interoperability model, Windows NT may be able to support ADSL out of the box.

Microsoft and partners are not alone in collaborating on an ADSL interoperability model. In February 1997, Motorola Semiconductor (Austin, Texas) and Sourcecom Corp. (Westlake Village, Calif.) partnered to develop a model for an ADSL Transmission Unit for the Remote End. The Motorola/Sourcecom team is developing a model for ADSL equipment at the physical, data link and networking layers. Similar to the Microsoft initiative, the purpose of this collaboration is to ensure equipment interoperability and to help equipment vendors meet the telcos' and ISPs' demands for interoperable ADSL equipment.

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