Paul, In TIA TR41, the proposal was made several times to write such a standard, but it never got off the floor. The good design of a voice switch (the way in which the device determines whether to process incoming signals or whether to ignore the incoming signals and allow transmission of outgoing signals) is a very intricate matter and those who believe they have the best voice switch(es), are not eager to part with that intellectual property.
I know this doesn't help you, but at least it tells you why you have trouble finding that public document. Ciao, Vic
