 TXE4E (Enhancement) was developed by STC and introduced in the late 1980s to update both TXE4 and TXE4A exchanges to provide similar features to those available on System X exchanges, including 'Star Services', CCITT 7 common-channel signalling and itemised call-logging.Analogue signalling on transmission circuits was replaced with the SS7 signalling system that was used on System X and AXE10.This provided the call gapping control that stopped exchanges being overloaded by too many incoming calls (an example being when newspaper competitions misprinted winning numbers).