Demand for faster Internet access and for cheaper and more flexible access via the normal analog telephone is getting higher and higher. Terms like Voice over IP (VoIP), Voice over ATM (VoATM), and Voice over DSL (VoDSL) are becoming more and more popular. This paper describes the requirements for the analog POTS interface in such systems, like Integrated Access Devices (IAD) and xDSL-Network Termination (xDSL-NT).