ITU-T Q.25 1988 Edition, November 1, 1988
SPLITTING ARRANGEMENTS AND SIGNAL RECOGNITION TIMES IN "IN-BAND" SIGNALLING SYSTEMS
Published By:International Telecommunications Union -Telecommunication Standardization Sector (ITU-T)
In each "in-band" signalling system precautions should be taken so that, when the signalling in that system is taking place:
no interference in the voice-frequency range from outside the system can pass into the system (i.e. into the transmission path between the sending end and the receiving end of the voice-frequency signals), and
as far as possible, no signalling current used in the system can pass into other systems, connected in tandem.