PD 6561-1992
修改件(草案):BS 6789 Pt.1-84"英国长途通信公共交换电话网连接用单功能或多种特别功能装置.第1部分:一般要求规范"
A draft amendment to BS 6789:Part 1:1984 "Apparatus with one or more particular functions for connection to the British Telecommunications public switched telephone network. Part 1. Specification for general requirements"