out+of+use
131fall out of use — cease to be used …
132out-of-band signaling — Use of narrowband filters to place the voice signal on a carrier channel below 3,400 cps, reserving the 3400 3700 cps band for supervisory signals …
131fall out of use — cease to be used …
132out-of-band signaling — Use of narrowband filters to place the voice signal on a carrier channel below 3,400 cps, reserving the 3400 3700 cps band for supervisory signals …