ETSI EN 300 953-2000 数字蜂窝通信系统(第2+阶段).呼叫等待(CW)和呼叫保持(HOLD)补充业务.第3阶段.GSM 04.83(版本7.0.1,1998年发布)
Digital Cellular Telecommunications System (Phase 2+); Call Waiting (CW) and Call Hold (HOLD) Supplementary Services; Stage 3 (GSM 04.83 Version 7.0.1 Release 1998)