Telecom market analysts predict that service providers will soon bundle Voice over DSL (VoDSL) with their small business DSL Internet access packages. VoDSL is a hybrid service designed first and foremost to reduce local access costs.
I have yet to purchase a VoDSL interface or speak with anyone who has one on-site, but by year's end the situation could be quite different. CopperCom, TollBridge Technologies and others offer integrated access devices (IAD) that seamlessly connect the small office and telecommuters' voice and data traffic directly to central office switches and wide area data networks, respectively.
Sharing the wire
Data and voice over the same copper -- it sounds familiar. But VoIP and VoDSL are different animals, designed to address different (though complementary) business needs. With VoIP, analog voice is digitized and packetized at the gateway or in the handset, and the voice-bearing packets pass through IP routers and switches to the VoIP gateway nearest their called party's location. Today's VoIP solution providers have built and are commercializing specialized IP infrastructure for low-latency end-to-end conditions. Due to changes in standards incorporated in voice/data gateways, including signaling protocols (e.g., H.323 or SIP) and compression algorithms, VoIP service providers' infrastructures have needed a lot of upgrades, interoperability testing, and management. Such value-added services as call recording, multipoint conferencing, call transfer, and caller ID are not on the current services menu. Nevertheless, offering simple point-to-point VoIP service across countries -- and particularly internationally -- is so much more economical than using circuit switches that the price per minute of VoIP is often one half or one quarter the cost of using a traditional service provider's network.
In contrast with VoIP, voice over DSL is not packetized. It is first digitized, then compressed by a standard adaptive differential pulse-code modulation (ADPCM) codec in the IAD and sent as a 32 Kbps digital signal over copper to a voice switch. A customer with a VoDSL-enabled handset (or an IAD and any analog handset) can get call waiting, caller ID, and any other service provisioned in central office voice switches.
All current DSL systems automatically and dynamically manage voice bandwidth separately from data services. Today, a single DSL line, using copper in place, supports as many as 24 ADPCM compressed point-to-point conversations between an IAD and central office voice switches without changing the customer's TCP/IP bandwidth allocation. You can also find IADs with smaller capacities for four or eight simultaneous calls.
My firm, PEREY Research & Consulting, fits the profile of the VoDSL target customer perfectly. We're a small concern with high recurring telecom costs. We pay Pacific Bell every month for four POTS lines at a cost of approximately $20 each (and three Basic Rate ISDN lines at $35 apiece for a 384 Kbps H.320 videoconferencing system). A VoDSL provider could significantly reduce what we pay for local access to a central office's circuits.
If a DSL provider offered voice "dial tone" in addition to high-speed Internet access in this area, we would be an easy sale. But that's not the final word on the subject, as we'll discuss next time.