They should not be relied upon to provide an error free method of relaying tone signalling to other decoders, such as a telephone exchange DTMF detector, for example.

它不应该被依赖用做提供一种无错的传送方法，传送双音频信号到另一解码器。例如：电话交换机的DTMF侦察器。

youdao

To this end, the requirements of the telephone service, the data transmission service and the signalling network management, in particular, were investigated.

为此，专门调查了电话业务、数据传输业务和信令网络管理的要求。

youdao

The report said that because of the layout of the rail line and signalling operators, anyone using the telephone line to discover if it was safe to cross could be told to wait up to 20 minutes.

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