Voice over DSL

Changing the economics of voice and data delivery.

This year, the potential of voice-over-DSL (VoDSL) technology will enable CLECs to provide multiline voice-telephony services to customers and reselling voice access to long-distance companies at prices dramatically lower than traditional telephony access.

Voice-telephony services are usually delivered using time division multiplex (TDM) equipment. In TDM systems, channels are dedicated to voice service. If the voice service is not active, the bandwidth that was allocated for voice will not be reused dynamically for data service.

Furthermore, these networks traditionally utilize a copper line dedicated for a single voice circuit. It would be difficult to justify leasing a single unbundled copper line, solely for offering voice- telephony service, since revenues from a single voice line cannot justify the costs of leasing the unbundled connection, especially for customer sites with 10 lines or less. However, technology that could integrate data with voice services onto a single copper line, such as voice-over-DSL technology, creates a value proposition for offices of all sizes. DSL technology achieves data rates of many hundreds of kbps over the majority of copper lines. A voice channel requires at most 64 kbps and, often, compression techniques allow much less. 

OVERLAYING VOICE SERVICE; VoDSL BENEFITS

A DSL access network can be upgraded to provide voice-telephony service at a small incremental cost. By combining voice gateway technology with DSL access technology, voice and data service can be integrated onto a single copper line infrastructure. The DSL access network is upgraded by the addition of two key components; the integrated access device (IAD) at the customer location and a gateway device usually located at the regional switching center.

The IAD is a new type of customer device. It receives and transmits data to/from the network over existing infrastructure; in this case, copper pairs using DSL modem technology. Data service is presented to the user by the IAD via traditional standardized interfaces, such as Ethernet (10Base-T) or ATM-25. In addition to data, the IAD presents multiple voice-telephony interfaces to the customer. This voice-traffic is digitized within the IAD and multiplexed onto the traffic to and from the network.

In most cases, the access network will be based on asynchronous transfer mode (ATM) technology. User data traffic may be carried in ATM virtual circuits (VC) to and from the network. The multiplexed voice traffic is transported in an additional VC, which is dedicated to voice. As voice channels become active within this VC, the system dedicates more bandwidth for voice in real time. Compression algorithms may be employed to reduce the bandwidth needs for the voice circuits. At the central office, the DSLAM processes an extra VC for each VoDSL customer. Since voice-telephony service is sensitive to time delays, it is important that the system gives priority to voice calls.

Voice traffic is carried within the VC through the regional ATM network to the carrier’s voice switch; and, at this location, the second component of the VoDSL network is employed. The voice gateway terminates the ATM VC and connects the voice circuits onto the traditional voice switch using a standardized digital interface, such as V5 or TR-303 (U.S.A.).

The true integration of voice service onto a broadband data access network offers many benefits. For CLECs who previously targeted data access, it opens up an enormous new revenue opportunity, as well as dramatic savings in operating costs. Only a single unbundled copper pair is needed to serve voice and data to most customers. In central office buildings, the cost of installing and maintaining separate TDM voice equipment is completely avoided, since nothing more than a DSLAM is needed. Both voice and data traffic can be multiplexed by the DSLAMs. Voice traffic is carried from the IAD within VCs through the existing DSLAM equipment, which may even be already under deployment for data-access services. Fiber-optic backbone connections also benefit, since only a single common back-haul circuit is needed to the regional point-of-presence or switching location. Furthermore, the regional network can enjoy the greater bandwidth efficiency of packet or cell networks compared to TDM networks, resulting in lower overall backbone network operating costs.

ATTRACTIVE NEW SERVICE PACKAGES

There is considerable past evidence that bundling voice and data services together in a single package results in improved customer acquisition and retention rates. The customer can also enjoy one-stop shopping for voice and data needs, as well as consolidated billing. However, the greatest weapon—and one where the enormous potential has yet to be unleashed—is to offer bundled service packages that dramatically undercut the prices of the incumbents while still maintaining good profitability. In the past, most bundled packages have been little more than exercises in tariffs. The true integration of voice and data on a common, bandwidth efficient access infrastructure enables the CLEC to offer some extremely attractive packages. One such example is free always-on high-speed Internet access to customers who switch to competitive long-distance telephone service carriers.

Once a carrier establishes a broadband access connection to a user, it becomes possible to offer narrowband services at a small incremental cost. This axiom may be about to radically modify the traditional economic model for narrowband access. Competitive carriers who have begun to deploy networks using unbundled user connections for data-access services are suddenly taking a much broader look at the opportunity to target voice service. The resultant integrated network benefits from maximum bandwidth efficiency and, hence, minimum costs at all points, including the access transmission connection, central-office equipment requirements, and fiber-optic back-haul connection. A business case analysis shows that multiline voice services can be added with only very modest cost increments to a DSL access network infrastructure, yielding large increases in revenue and a dramatic improvement in return-on-investment. These advantages, when compared to traditional separated voice and data architectures, are expected to result in yet a further acceleration in the battle for the customer and bring some very dramatic changes in our future telecommunications landscape.

Cole is vice president of business development in North America for Orckit, San Folsom, Calif. www.orckit.com