| 单词 | E-1 |
| 释义 | E-1 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 × 8,000 per second = 64,000 bps, or 64 kbps).Taken together, the 32 8-bit time division multiplexed (TDM) channels at 8,000 fps yields an aggregate payload signaling rate of 2.048 Mbps (32 channels × 64 kbps = 2.048 Mbps). Of that total, the two signaling and control channels consume 128 kbps (2 × 64 kbps = 128 kbps), leaving the user payload transmission rate at 1.920 Mbps. E-1 was designed to operate over an unshielded twisted-pair (UTP) circuit comprising two two-wire pairs, each of which operates in simplex mode. One pair supports transmission in one direction and the other pair, in the opposite direction. In the aggregate, the physical four-wire circuit supports full-duplex (FDX) transmission. The line coding technique employed in traditional E-1 is alternate mark inversion (AMI), which yields 2.048 Mbps at a nominal carrier frequency of 1.168 MHz, which is exactly half the TDM TDM MUX MUX 31 31 ... 2 0 31 ... 2 0 31 ... 2 0 31 CSU CSU DSU DSU 0 2 ... 31 0 2 ... 31 0 2 ... 31 0 2 Frame = 32 octets = 256 bits 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Synchronization Signaling 1 0 0 1 1 0 0 1 Byte = Octet |
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