The first level of the European E-carrier digital hierarchy. An E-1 system comprises circuit terminating equipment in the form of a combination of a channel service unit (CSU) and 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. E-1 operates at a signaling rate of 2.048 Mbps, which supports a frame rate of 8,000 frames per second (fps), with each frame comprising 32 eight-bit time slots, 30 of which are for user payload and 2 of which are set aside for signaling and control data. As illustrated in Figure E-1, time slot 0 (zero) is used for synchronization and alarming.Time slot 16 is used by the equipment for all signaling functions, such as circuit monitoring and diagnostics. 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.
Webster's New World Telecom