1)local central office,市话局2)SPC local exchange,程控市话局3)SXS local exchange,步进制市话局4)local exchange,市话交换机（局）;市话局;本地交换局5)central office(CO),telephone central office,中央电话局，中心局，市话局6)line,市话
用法和例句
Application of radio and line mixed transmission in automatic delivery of barreled water;