为此，我们引入了后备模式的概念。

So, the concept of fallback mode is presented.

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介绍城市轨道交通中，移动闭塞系统的后备模式的由来、定义及其功能。

This paper describes the origin, definition and function of fallback mode of moving block system for urban rail transit.

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如果扩展了LDAP模式，那么必须维护修改，并在修改之前和之后备份整个目录。

If you have extended LDAP schema, you must maintain the changes and back up the entire directory prior to and after the change.

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