This document describes a communication interface between a channel and I/O control units that utilize the Single-Byte Command Code Sets (SBCCS) as implemented in a wide range of data processing systems. It employs information formats and signaling protocols that provide a uniform means for communicating with various types of I/O control units, facilitating a high-bandwidth, high-performance, and long-distance information exchange environment. The signaling protocols and information exchanges are defined at a layer (FC-4) to compatibly utilize the link services and other functions provided by the INCITS Fibre Channel Framing and Signalling (FC-FS-3) and the INCITS Fibre Channel Link Services (FC-LS-2) specifications. This FC-4 Upper Level Protocol is referred to as the Fibre Channel-Single-Byte-4 Command Code Sets Mapping Protocol (or for brevity, SB-4). FC-SB-4 modifies FC-SB-3 to include optional support for the transport mode of operation that allows multiple, single- byte I/O commands to be sent to a control unit in a single Information Unit. Transport-mode operations utilize device-level protocols similar to those described in the FC-4 Fibre Channel Protocol (FCP-4) specification.