The use of bit interleaving, and the presence of stuffing bits in the multiplexed data stream, means that it is virtually impossible to extract data belonging to an individual channel or tributary without de-multiplexing the high-level data stream down to the required level. To extract a single 64 kbps channel from a 565.148 Mbps trunk, the complete hierarchy of de-multiplexers is required as shown in the illustration below. The same principle applies to inserting a channel or tributary into a multiplexed data stream.