D-channel voice communications

Abstract

A number of proposals have been developed to provide data communications over two-wire copper circuits at rates equivalent to a number of combined ISDN B-channels. For example, for an ISDN rate digital subscriber line (IDSL), the circuit between the network termination at the customer premises and the channel bank carries data on two combined B-channels. An IDSL circuit cannot carry voice communications. Some such services carry the lower rate signaling D-channel only on the subscriber line circuit. Normal ISDN services carry voice services on one of the two B-channels, limiting data communications to the other B-channel. Normal ISDN services do carry the lower rate D-channel through the network, but this channel is used only for call set-up signaling, low speed data communications and the like. The invention uses two or more B-channels on the DSL circuit for data communications and transports voice telephone communications on the low speed signaling D-channel. The bearer (B) channels typically connect to a high speed data network, such as SMDS, for services such as Internet access. The voice communications on the D-channel utilize in-band call set-up signaling and appropriate CODECs for digital communications compressed to the low D-channel rate. The channel bank includes a multiplexer/demultiplexer to combine four active D-channels voice communications into one DS0 for transport to a switch module, for example, in an end office telephone switch.