High speed communications system for analog subscriber connections

In a communication system that includes an encoder and a decoder, wherein the encoder has a digital connection to a digital portion of a telephone network and the digital portion of the telephone network is connected by an analog loop to the decoder, wherein the analog loop converts digital information from the network into analog voltages for transmission to the decoder, a method of detecting the presence of robbed-bit signaling within the digital portion of the telephone network comprising the steps of:

• sending a predetermined pattern of PCM codewords from the encoder to the digital portion of the telephone network;
• receiving said predetermined pattern of PCM codewords in the form of analog voltages at the decoder;
• determining an error measurement at the decoder in response to said received analog voltages;
• and
• determining whether robbed-bit signaling is present based upon said error measurements.