With DSL technologies, the same cables that provide plain old telephone service (POTS) to customers are also used to provide high-bit-rate digital services to the end users. Because the bandwidths used in DSL systems are significantly greater than the voice band, so considerably higher bit rates are achieved. In the cable, these wideband signals radiate energy that is absorbed by other pairs in the cable, and the energy appears as crosstalk. Crosstalk is one of the key impairments that limit the performance of DSL systems.

Different DSLs in the cable utilize different bandwidth. Depending on the energy of the signals and the spectral placement, the different types of DSL systems may or may not be compatible with each other. The crosstalk effect that one DSL system has on another in the cable defines their spectral compatibility. In the design of DSL systems, spectral compatibility is important because the deployment of any new DSL services should not degrade the performance of other services in the cable. Likewise, the existing services in the cable should not prevent the new DSL from meeting its performance objective.

The tutorial describes the spectral compatibility of the echo-canceled (EC) transmission DSL systems relative to other DSLs deployed in the loop plant. The transmission DSLs included are ISDN, HDSL, and SDSL. For all spectral compatibility studies done in this tutorial, only 50-pair cables with 26-gauge wire are assumed in each case.