loop signaling repeater 环路信令中继器

DC loop signaling 直流环路信令

LSR Loop Signaling Repeater 环路信令中继器

Telephone Instruments with Loop Signaling 带环路信令的电话设备

loop signaling detail 环路发信

Signaling Loop Interruption LD 信令回路中断

Loop start signaling 回路起动讯号

loop disconnect signaling system 环路断续信系统

Signaling Loop Interruption LDj 信令回路中断