The interchange circuits conform to CCITT recommendation X20
Interchange Interchange Circuit Num. Name G Signal ground or common return Ga DTE common return Gb DCE common return T transmitted data R Received data
The electrical characteristics conform to CCITT recommendation V.11 (X.27/RS422/RS485) "Electrical characteristics for balanced double-current interchange circuits for general use with integrated circuit equipment in the field of data communications".
Despite that statement, quite a few system use V24/RS232; Gordon
The connector specification conforms to ISO 4903, 15 way 'D' type.
Don't trust that people comply to that. Many are 9 or 25-way 'D' types; Gordon
Pinout is defined in ISO4903, not sure how widely used (we had a 25-way D-type with other services on it also); Gordon
600 Ohms balanced with respect to earth, Signal adjustable between -6dBm and -20dBm.
Many (most?) systems working via Espa 4.4.4 have no speech or speech paths; Gordon
All standard Baud rates between 300 and 9600 are available.
I think most default to 1200; Gordon