J2 meaning

The second level in the Japanese J-carrier digital hierarchy. J-2 runs at two signaling rates. At 6.312 Mbps, J-2 mimics the North American T2, comprising four J-1s at 1.544 Mbps each, plus 132 kbps of overhead and justification, or bit stuffing, to adjust for variations in the clocking rates of the incoming J-1s. Multiplexing is performed by M12 (Multiplex J1-to-J2) terminals that multiplex four J-1 signals, which yields 96 DS-0 channels at 64 kbps per channel. At 7.786 Mbps, J-2 supports 120 DS-0 channels, which maps J-2 into E-2, the European version. Despite similarities in terms of signaling rates and channel capacities, J-carrier is not compatible with either E-carrier or T-carrier. See also bit stuffing, digital signal hierarchy, DS-0, E-2, E-carrier, J-carrier, T2, and T-carrier.
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