System Y

System Yis the terminology used byBT,the main operator of the telephone network in theUnited Kingdom,to refer to theEricsson AXEdigital switching system.

In the mid-1980s, British Telecom chose the well establishedAXE10digital switch to provide competition forSystem Xdeveloped by a consortium ofPlessey,General Electric Company(GEC) (companies later combined as GPT),STCand BT's state owned predecessor, theGPO.The newly privatised BT brought in Ericsson as a competitive alternative supplier ending Plessey/GEC's monopoly on the provision of switching systems.

Initially, the AXE systems installed in the UK were partially locally manufacturered in partnership withThorn EMIand later directly by Ericsson. While System X exchanges were more widespread in BT's network, AXE10 (and subsequent versions) remain common in the classic BTPSTNuntil their eventual replacement when the network is closed, which at the time of the writing is expected to be in 2025^[1]

AXE10 covers two main types ofdigital telephonyswitching equipment: the remote subscriber switch (RSS) and the AXE10 local switch. RSS acts as aremote concentratorand deals with the conversion of analogue telephony signals used in theaccess network,which is the copper pairs between exchange buildings and customer premises, also calledlocal loop,and the multiple xing 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,^[2]is maintained in house by its own engineers althoughEricssonstill provide high-level support, software upgrades and repairs at component level.

AXE/System Y, System X and otherTDMtechnologies are already being be phased out as BT, in common with many networks around the world, implements its next generation access network, which will ultimately be based predominantly on fibre to premises (FTTP), with voice services provided usingVoIPtechnology.^[3]