DSL Comes Home-with a Network - Industry Trend or Event

Just when the communications industry finally seems to be getting handle on the numerous flavors of Asymmetical Digital Subscriber Line (ADSL) technology, new questions are arising about how ADSL relates to another hot technology: home networking.

First, let's clear up any confusion that may be lingering. The various types of ADSL and home networking technologies ultimately concern pumping Internet data at faster and faster speeds into and throughout consumers' homes. It is our belief that the technologies are complementary and will be two of the key engines driving the mass deployment of broadband services in consumers' homes.

The newest specification for consumer DSL service, G.Lite, can be thought of as a consumer-installable form of DSL. It can be deployed economically because it does not require installation in the home of a piece of equipment called a voice/data splitter. G.Lite converts analog telephone lines into digital lines by adding a line-interface device in the telephone company's central office and a DSL modem at the subscriber's home. Customers also must subscribe to DSL service from their telephone service provider. G.Lite can transmit Internet data into peoples' homes at up to 1.5Mbits/sec., about 25 times faster than today's fastest analog modems.

Home networking uses existing copper home phone wiring to create a consumer-friendly home network that allows for simultaneous access of the Internet using two or more PCs. In addition to the outside-the-home broadband, there is the growing need to move data between devices within the home. Home networking also allows two or more PCs within a home to share printers or other peripherals. All of this can be done at initial speeds of 1Mbit/sec. and eventually at 10Mbit/sec. using one modem connection, one telephone wire, and one Internet Service Provider.

Broadband to the home via ADSL and broadband in the home via home networking are certainly inter-related in that both are enablers in the digital connectivity application space. However, ADSL and home networking deliver different benefits to consumers and use different technologies to achieve these benefits.

G.Lite aims to provide Internet services to homes in the 28KHz to 1.5MHz frequency spectrum. Home networking uses the frequency band between 4MHz to 10MHz to provide connectivity for multiple devices within the home. Home networking technology is about creating a local area network and using that network for simultaneous, multiple device, and high-speed Internet connectivity within a home.

Broadband to the home via DSL and home networking via phone lines are both designed to be plug-and-play technologies which enable the consumer to get the capability by simply plugging in the equipment without needing a visit from a service technician. Broadband to the home and broadband in the home are synergistic from a use perspective as well. With a bigger pipe into the house, multiple PCs can access the Internet simultaneously at faster rates using G.Lite technology.

As an emerging standard for DSL, G.Lite has a feature called fast retrain that allows the modem to adapt to events on the phone line such as ringing, answering the phone, and hanging up the phone. The data rates will momentarily change and then settle out as the modem quickly retrains for the changes in the home wiring impedance and noise levels. These changes to the phone line by design do not translate into significant changes in the data rates, nor in most cases are the data rate changes that may occur noticeable by the user from a perceived throughput perspective.

The Home Phoneline Networking Alliance (HomePNA), an industry consortium driving toward a standard for home networking, has developed home networking protocols. Some may wonder whether these protocols will affect DSL transmissions. The answer is no, provided your design-band limits itself properly and presents a proper impedance to the phone line. Home networking boards need to be designed with DSL and analog services in mind, while DSL boards must be designed with analog voice and home networking in mind.

Some in the industry have expressed concern that when supporting all three services voice, ADSL and home networking-that lines might suffer from cross-talk, which happens when signals bleed over from one line to adjacent lines in the wiring bundle. But since the voice, ADSL and home networking signals run at different frequencies, they do not clash on the line.

A protocol developed by Lucent Microelectronics Group, which has been submitted to the HomePNA, addresses the cross-talk issue. Under the protocol, home networking signal traffic operates in the 4 to 10MHz band range. DSL traffic runs at 26 to 550KHz for G.Lite, and at 1.1MHz for full rate ADSL, a faster flavor of DSL that runs at speeds of up to 8Mbit/sec. Voice traffic runs in the 300 to 3,300Hz range. A reasonable guard band between each operating bandwidth provides isolation and prevents cross-talk.