Bellcore Technical Reference TR-303 requires that SONET- based Remote Digital Terminals (RDTs) use the Common Signaling Channel (CSC) for timeslot management of DSOs that are transported bytesynchronously in SONET virtual tributaries. However, initial switch offerings of the TR-303 Interface are expected to only support the Timeslot Management Channel (TMC) for timeslot management of DSOs that are transported via standard Extended-Super-Frame (ESP) DSls. This marketplace reality forces telephone companies, on the one hand, to deploy a SONET network element in the central office to convert the OC-N (currently N - 1, 3, or 12) signal into DSls and transmission vendors, on the other hand, to support additional capabilities associated with TMC. This paper discusses two transitional interoperability concerns associated with byte-synchronous SONET-based RDTs. The first concern is with the availability of needed SONET byte-synchronous capabilities in the central office. The second concern is with the complexities that arise when the TMC method for timeslot management is utilized until the CSC capability becomes available via a direct SONET-IDLC interface to the switch. This paper also discusses the transitional Digital Loop Carrier (DLC) solutions being offered by transmission vendors to address these transitional interoperability concerns. Steps involving any changes in the SONET mapping/format requirements have been ruled out, thus not jeopardizing SONET-equipment availability and allowing industry to move forward on the Generic SONET-IDLC Interface at the switch.