The all digital loop: benefits of an integrated voice-data access network

With the evolution towards the multi-service network, voice and data, today's most important services, will be transported over a single network infrastructure. Although digital subscriber line (xDSL) systems can already transport both services simultaneously over a single twisted telephone pair, they still use separate frequency bands. There is a tendency to carry the telephony signal in-band, as part of the digital data stream. This paper discusses several benefits of an integrated voice-data access network based on xDSL. In a DSL-based solution carrying voice in-band, the bulky plain old telephone service (POTS) splitter that is normally required to separate voice and data becomes superfluous, resulting in higher density. An all-digital loop can use the lower part of the frequency spectrum that was reserved for POTS. Simulations have shown that the flexibility and high spectral efficiency of discrete multitone modulation (DMT) increase the capacity or reach. The lifeline service for voice is also considered. A DSL low-power mode, which only uses the elements needed to support voice service, can help achieve this goal