DIN ETS 300283-1994 商务电信(BTC).与公共网络数字连接的专用网络用响度值和回波值的设计; 英文版本 ETS 300283:1994
Business TeleCommunications (BTC) - Planning of loudness rating and echo values for private networks digitally connected to the public network; English version ETS 300283:1994