A hierarchy of standards for digital transmission that essentially is the Japanese version of the United States T-carrier digital carrier system.At levels one and two, J-carrier mimics T-carrier with respect to the signaling rates, but diverges at level three and beyond. J-carrier also uses a different PCM companding technique (A-law rather than µ-law). As J-carrier is medium-independent, it can be provisioned over any of the transmission media, at least at the J-1 rate of 1.544 Mbps. (At the J-3 rate of 32.064 Mbps, twisted pair is unsuitable due to issues of signal attenuation.) The fundamental building block of J-carrier is a 64-kbps channel, referred to as DS-0 (Digital Signal level Zero).Through time division multiplexing (TDM), J-carrier interleaves DS-0 channels at various signaling rates to create the services that comprise the Japanese digital hierarchy, as detailed in Table J-1.

Table J-1: Japanese Digital Hierarchy: J-carrier

J-carrier Level	Data Rate	64-kbps Channels (DS-0s)	Equivalent J1s
0	64 kbps	1	Not applicable
J-1	1.544 Mbps	24	1
J-2			4 5
J-3	32.064 Mbps	480	20
J-4	97.728 Mbps	1,440	60
J-5	565.148 Mbps	7,680	320

See digital signal hierarchy for a side-by-side comparison of the North American, European, and Japanese digital hierarchies. See also A-law, carrier, channel, companding, digital, DS-0, E-carrier, J-1, J-2, J-3, J-4, J-5, µ-law, PCM, signaling rate, T-carrier, and TDM.