ssion class provides methods which can be used for authoriza- tion, depending on the nature of the authorization scheme for any particular user. There are also classes that extend ConfigPermission which have been defined so that more specific methods can be accessed while checking the permission for task, device list and data source. 41 11.2.7 Rollback The rollback functionality allows any user-specific operation to be performed, such as restoration of older configuration data, when any single device cannot be config- ured. Rollback can occur for a device either by using current configuration or by using a rollback document. Suppose a task is executed over 10 devices and the task is intended to change the location of those devices. If the task is executed, then all 10 devices will be config- ured so that they have the modified location value. While executing the task, if a device cannot be configured or accessed, then it may be desirable to restore the older values to all the devices. This is a case where current configuration is used. "Current configuration" is where the server collects and stores older configura- tion data from the devices before configuring them. The task is then applied to the 41 Such a class is known as a sub-class. OSS for Telecom Networks set of devices, either sequentially or in parallel, as specified. If configuration of any one of the devices fails, then the CMS will attempt rollback to restore the older con- figuration values to those devices which have already been configured. After this, the configuration of other devices in the set will not be attempted. It may be desirable to execute a task if any of the devices refuses configuration. In this case, an existing task can be set as a "rollback document". In this scenario, CMS starts the configuration and if any device's configuration fails, further configuration ceases and the rollback document will be applied to the already configured devices. When configuring a large number of devices, if one device fails then the rollback will be a