What is the difference between T1 and J1?
A3. J1 commonly refers to the derivation of the North American T1 standard that is used exclusively in Japan. Differences exist between J1 and T1 in the yellow alarm generation for superframe (SF) and extended superframe (ESF) modes. Also, the CRC-6 calculation in ESF mode is different. In J1 SF mode, the yellow alarm is generated when a ‘1’ is transmitted in the 12th F-bit, as opposed to T1 SF mode in which a ‘0’ is transmitted in the 2nd bit of all timeslots. In J1 ESF mode, the yellow alarm is generated by transmitting ‘FFFF’ in the data link (DL) section of the F-bits, as opposed to T1 ESF mode in which ‘FF00’ is transmitted in the data link. In J1 ESF mode the CRC-6 calculation includes the frame alignment signal and data link F-bits. However, for T1, all of the F-bits are set to ‘1’ when the CRC-6 calculation is performed.
