This single-width port adapter provides two T3 interface connections using BNC connectors. Each T3 interface can be independently configured to be either channelized or unchannelized. A channelized T3 provides 28 T1 lines multiplexed into the T3. Each T1 line can be configured into one or more serial interface data channels. An unchannelized T3 provides a single serial interface data channel that may be configured to use all of the T3 bandwidth or a fractional portion of it. This mode is compatible with several vendors of fractional (subrate) DS3 data service units (DSUs).