While voice over DSL is a misnomer, the technology promises to offer customers savings soon.
So far, there's been lots of talk and little action about voice-over-digital subscriber line services -- but that situation is about to change.
Just last week, two service providers announced plans for voice-over-DSL services, and others hinted that they would come out with similar offerings soon.
When the services become a reality, customers can expect lower prices and a single line that delivers voice and data services, which have been provisioned in the past over T-1 lines.
One of the first carriers to latch on to voice over DSL is Network Telephone, a new carrier in Florida. The carrier says it will sell combined voice, data and internet access services over DSL by year-end using gear from Lucent and Copper Mountain.
TelePacific Communications, a local voice/data/internet provider based in Los Angeles, plans to use Jetstream Communications and Cisco gear to support voice and data services over DSL soon. The carrier is testing the technology at a customer site now.
Neither service provider would share specifics on prices or rollout schedules.
Meanwhile, nationwide DSL specialists Covad and NorthPoint say they will announce voiceover-DSL services, probably within the next few months.
Spokesmen for NorthPoint and TelePacific say they are waiting to see whether equipment necessary to support such services is ready for the rigors of carrier networks.
DSL is known best as a data technology that can add a multimegabit data stream to a regular phone line. With some flavours of DSL, the data channel can be added without disrupting the standard analog voice channel on the line.
But that's not the voice referred to in the term voice over DSL. Voice over DSL is more accurately described as voice over IP over DSL or voice over ATM over DSL.
A box at the customer site, called an integrated access device, connects to the local data network and the office phones. Voice and data traffic is converted to IP packets or ATM cells and crosses a DSL link into the carrier network.
The carrier network sorts the packets or cells and routes them to the appropriate destinations. If voice is to be delivered over the public voice network, a conversion box inside the carrier network, known as a voice gateway, makes the needed conversion.
This gateway also takes the call features and phone services -- such as caller ID, Centrex, call waiting and three-way calling -- that reside on voice switches and delivers them to voice-overDSL customers.
Voice over DSL came to light late last year when start-up Jetstream announced at the ADSL Forum that it was working on a voice gateway. Since then, big-name companies such as Lucent, Cisco, Nortel Networks and Siemens have joined the market.
Vendors are busily working to provide interoperability among their products. For example, more than 15 makers of customer gear have licensed Jetstream's technology to include in their integrated access devices.
Jetstream, in turn, has shown interoperability with Nortel, Lucent and Siemens voice switches -- devices that would have to connect to the Jetstream box to deliver voice calls.
An important consideration is that, unlike regular phone lines, DSL voice lines don't work when the electricity fails. So vendors have to figure out what to do when power to the integrated access devices is cut off, says Claudia Bacco, director of DSL products for TeleChoice, a telecomms consultancy in Boston.
She expects equipment makers to work out those problems in a timely fashion and to be able to deliver services soon.
With voice capabilities, DSL services become even stronger competitors to T-1 lines, which have been used to carry voice and data for years, says Chip Ach, chief technology officer for Harvard.net, a New England DSL vendor. DSL is already less expensive than T-1 for similar bandwidth, and requires a single pair of wires rather than the two pairs required by T-1.
But George Hu, product manager for voice products at NorthPoint, says that cooperation of established telephone companies will be crucial.
DSL carriers lease the actual wires that DSL runs over from the established carriers. If something goes wrong with the wires, the DSL carrier needs to rely on the established carrier to fix them.
So far, the DSL carriers cannot get guarantees that the lines will be fixed as fast as T-1 lines get fixed, Hu says.
Another problem DSL faces is that it is not universally deployed, whereas T-1 lines are available just about everywhere.
And it will take actual services to prove whether voice over DSL can be trusted, Ach says. "The jury's going to be out until people actually use this technology," he says.