ETSI PRETS 300 084-1990 综合业务数字网(ISDN).可用于3.1 KHz音频信息传输端到端兼容性的电路模式结构承载业务分类(T/TE12-08)
Integrated Services Digital Network (ISDN): Circuit Mode Structural Bearer Service Category Usable for 3.1 KHz Audio Information Transfer End-to-End Compatibility (T/TE 12-08)