A coding technique that transmits T1 data at 1.536Mbps by inserting the pattern 00011011, with BPV´s in the fourth and seventh positions, wherever ones density requirements are not met by the unmodified data.  It requires the CSU to not remove bipolar violations, and works only where the phone company equipment can tolerate it. This allows 64Kbps channels on a T1 (for example) rather then the base 56Kbps.