Public Switched Telephone Network (PSTN); Subscriber Line Protocol over the Local Loop for Display (and Related) Services; Part 2: Off-Hook Data Transmission
"This second part of ETS 300 659 specifies the subscriber line protocol for the support of PSTN display services at Local Exchange in ""off-hook"" state by using asynchronous voice-band FSK signalling. This specification is a complement of part 1 that deals with ""on-hook data transmission associated or not associated with ringing"". This ETS contains only differences and extensions to ETS 300 659-1 [1]."