GB/T 7720-1987 in English

《GB/T 7720-1987长途电话半自动对端设备技术要求和测试方法》由339-2（工业和信息化部（通信））归口，主管部门为工业和信息化部（通信）。
本标准适用于长途电话半自动对端设备。该设备作为终端设备用于两城市的长途电话局间，通过长途直达电路，实现长途电话半自动接续，也可经长途电话在交换机纳入全国长途自动电话网。

Scope

This standard applies to semi-automatic peer equipment for long-distance calls. This device is used as a terminal device between the long-distance telephone offices of the two cities. Through the long-distance direct circuit, the long-distance telephone connection can be realized semi-automatically, and it can also be included in the national long-distance automatic telephone network through the long-distance telephone exchange.