ETSI ETR 254-1996
公用交换电话网(PSTN).信令系统R2.通过欧洲通信卫星(ECS)进行的信令和电路监控(CEPT建议T/CS 42-09 E(1985))
Public Switched Telephone Network (PSTN); Signalling System R2; Signalling and Circuit Supervision Via the European Communications Satellite (ECS) (CEPT Recommendation T/CS 42-09 E (1985))