| 单词 | J-1 |
| 释义 | J-1 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 × 8,000 per second = 64,000 bps). Taken together, the 24 8-bit TDM channels at 8,000 fps yields an aggregate payload transmission rate of 1.536 Mbps. Adding the 8,000 framing bits (one per frame) per second, yields the aggregate signaling rate of 1.544 Mbps. J-1 was initially designed to operate over a physical four-wire twisted-pair copper circuit, but is considered medium independent and will run over coaxial cable, optical fiber, microwave, satellite, and free space optics (FSO) just as well. J-1 generally is used in local loops and other short-haul applications. In long-haul applications, J-3 and other, higher speed, standards generally are employed. See also carrier, CSU, DS-0, DSU, FDX, four wire, frame, framing bit, J-3, J-carrier, payload, signaling rate, synchronization, T1, T-carrier, TDM, time slot, and transmission rate. |
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