System Y

System Y is an electronic switching system and digital telephone exchange used by BT, the operator of the telephone network in the United Kingdom. 
In the mid-1980s, British Telecom decided to use the AXE10 digital switch to end its reliance on System X from Plessey and General Electric Company (GEC) (companies later combined as GPT). This kept Plessey/GEC from using a position of dominance to charge BT unfair costs of provisioning System X equipment parts. Although System X is more abundant in BT's network, AXE10 is still widespread in Britain.
AXE10 covers two main types of digital telephony switching equipment: the remote subscriber switch (RSS) and the AXE10 local switch. RSS acts as a remote concentrator and deals with the conversion of analogue telephony signals used in the access network, which is the copper pairs between exchange buildings and customer premises, also called local loop, and the multiplexing of customer lines over cabling to the AXE10 local switching unit. The AXE10 local switch uses a processor-controlled switch to route calls and data depending on the destination of the telephony transmission.
BT's AXE10 network, which has been in service since 1986, is maintained in house by its own engineers although Ericsson still provide high-level support, software upgrades and repairs at component level.
Both System Y and System X are likely to be phased out as BT implements its 21st Century Network based on VoIP and replacing existing switches, ADSL and analogue equipment with fully digital multi-service access nodes (MSAN).