Abstract: A method and apparatus for determining whether a sufficiently clear digital path exists from a first end user to a second end user when connecting a call over a switched telephone network. Once the determination is made, the type of connection that is possible (high speed digital or analog compatible rates) can be determined. The present invention determines the characteristics of a path between two subscribers on a telephone network by transmitting a digital probe along the path. In cases in which an answering subscriber or the intermediate path are incapable of supporting a digital call, communication in accordance with a standard analog modulation scheme can proceed without having to redial the call.