ETSI ETR 252-1996 公用交换电话网(PSTN).信令系统R2.线路信令的模拟和数字版本之间的转换(CEPT建议T/CS 42-04 E(1984))
Public Switched Telephone Network (PSTN); Signalling System R2; Conversion between Analogue and Digital Versions of Line Signalling (CEPT Recommendation T/CS 42-04 E (1984))