The first level of the Japanese J-carrier digital hierarchy. J-1 mimics the North American T1 system. A J-1 system comprises circuit terminating equipment in the form of a combination of a channel service unit (CSU) and a data service unit (DSU) that jointly serve to interface a device to a full duplex (FDX) four-wire digital circuit and to perform various signal formatting, signal timing, monitoring, and diagnostic functions. J-1 operates at a signaling rate of 1.544 Mbps, which supports a frame rate of 8,000 frames per second (fps), with each frame comprising a framing bit followed by 192 bits of user payload.The framing bits are used for synchronization and, in some cases, for monitoring, diagnostic, and other network management purposes. The 192 bits of user payload are organized into 24 time-division multiplexed (TDM) time slots, each of which is 8 bits wide.At a rate of 8,000 fps, each time slot is repeated 8,000 times per second, which translates into a DS-O channel at 64 kbps (8 bits.