An integral part of ISDN (integrated-services digital network) is the provision of full-duplex digital transmission capability at the basic access information rate of 144 kb/s over voice-grade metallic subscriber lines with all the associated disturbances from echo, intersymbol interference, and crosstalk, among other things. The authors provide an overview of the transmission environment and discuss the structure of transceivers for such use. Line coding, equalization, echo cancellation, and timing recovery are discussed at some length. A few numerical examples are given to illustrate the theoretically optimal transmission performance that can be attained with minimum mean-squared error equalization. Considerations regarding VLSI implementation of transceivers are briefly addressed.