available time of a service

The service provider guarantees that the services it provides will be available for a certain percentage of time (for example, 99.9%).

服务提供者保证它提供的服务在一定百分比的时间内(例如，99.9%)是可用的。

Once a new version of the service becomes available, the old version is declared deprecated, indicating that it will be decommissioned after certain period of time.

服务的新版本可用后，将旧版本声明为已弃用，表明在一段时间后将使其退役。

Prevent denial of service attacks: Using XKMS to get key information is useful if it is available when needed and within a reasonable amount of time.

防止服务的抵赖攻击(denial of service attack)：使用XKMS来获取密钥信息比较有用，前提是XKMS在需要的时候可用，并且这一过程能在合理的时间内完成。