PSTN Exchange development stages
nRegister-controlled setup
nB-subscriber number receiver by a register
nregister controls all the remaining call setup stages
nDistributed control
nMarkers indicate idle switches
nThus markers control path routing
nStored program control (SPC)
nNew services
nIntegrated charging
nEasier updating and maintenance
n
Text Box: 1960 and before
1960 and before