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All analog circuits use ground start. For T1, channelized (CAS) and ISDN PRI. E1 uses ISDN PRI only. For T1 CAS the protocols are Loop Start, Ground Start, E&M Immediate Start, and E&M Wink Start. For T1 ISDN PRI or ISDN BRI, the protocols are ETSI (on E1), Lucent Custom, Nortel Custom, and National NI2 (on T1).
