A common technique for transporting call control signals over a digital telecommunication network, such as, but not limited to a T-1 data rate network, is the use of `robbed`-bit signaling, in which least significant bits are `robbed` from selected DS0 communication channels and used instead for the transport of in-band signaling information (termed ABCD bits). Although in-band, robbed bit signaling allows the service provider to use all of the available TDM channels for customer traffic, and has been found to be generally acceptable for the transport of quantized voice, it can constitute a significant impairment to the quality of transported data traffic.
This data traffic degradation problem can become particularly exacerbated in networks containing a plurality of concatenated signaling discontinuities, such as repeaters and/or cross-connect nodes--that do not allow DS1 extended superframe alignment to maintained. Since the robbed bits cannot be tracked across these discontinuities, a series of three dB noise penalties may be incurred. One possible alternative of using one of the (twenty-four) communication channels as an out-of-band channel for the transport of signaling information for the remaining twenty-three `clear` DS0 communication channels is unacceptable to telecommunication service providers as a cost prohibitive allocation of resources and usurping of useful DS0 bandwidth.