It describes generic procedures, network specific facilities and end-to-end signalling methods.
它描述了通用程序、网络特定的性能和端到端的信令方法。
Low voltage surge protective devices - part 21: surge protective devices connected to telecommunications and signalling networks - Performance requirements and testing methods.
低压电涌保护装置。第21部分：与电信和信令网络连接的电涌保护装置。性能要求和试验方法。
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