A digital subscriber link data network incorporates a throughput test server (TTS) to provide fault identification, isolation, and verification of DSL service availability and data rates. An asymmetric digital subscriber line (ADSL) terminal unit-remote (ATU-R) is connected to an ADSL terminal unit-central office (ATU-C) over a conventional copper loop or equivalent. Data connectivity via a packet switch provides access to high speed data networks, TTS connectivity and interfaces to service providers (SPS). Upon receiving a test request, a technician routes a customer to the TTS. The customer uses a web browser to access the TTS and download executable testing software, e.g., a JAVA applet. The applet causes test messages to be sent to and received from the TTS and computes upstream and downstream data rates that is displayed to the customer together with whether the measured data rates are consistent with a specified class of service.