+ The term refers to a resource that enables the creation\r
+ of virtual environments on top of the physical resources, e.g.\r
+ hypervisor, OpenStack, etc.\r
+\r
+Upgrade Campaign\r
+ The term refers to a choreography that describes how the upgrade should\r
+ be performed in terms of its targets (i.e. upgrade objects), the\r
+ steps/actions required of upgrading each, and the coordination of these\r
+ steps so that service availability can be maintained. It is an input to an\r
+ upgrade tool (Escalator) to carry out the upgrade.\r
+\r
+Upgrade Duration\r
+ The duration of an upgrade characterized by the time elapsed between its\r
+ initiation and its completion. E.g. from the moment the execution of an\r
+ upgrade campaign has started until it has been committed. Depending on\r
+ the upgrade method and its target some parts of the system may be in a more\r
+ vulnerable state.\r
+\r
+Outage\r
+ The period of time during which a given service is not provided is referred\r
+ as the outage of that given service. If a subsystem or the entire system\r
+ does not provide any service, it is the outage of the given subsystem or the\r
+ system. Smooth upgrade means upgrade with no outage for the user plane, i.e.\r
+ no VNF should experience service outage.\r
+\r
+Rollback\r
+ The term refers to a failure handling strategy that reverts the changes\r
+ done by a potentially failed upgrade execution one by one in a reverse order.\r
+ I.e. it is like undoing the changes done by the upgrade.\r
+\r
+Restore\r
+ The term refers to a failure handling strategy that reverts the changes\r
+ done by an upgrade by restoring the system from some backup data. This\r
+ results in the loss of any data persisted since the backup has been taken.\r
+\r
+Rollforward\r
+ The term refers to a failure handling strategy applied after a restore\r
+ (from a backup) opertaion to recover any loss of data persisted between\r
+ the time the backup has been taken and the moment it is restored. Rollforward\r
+ requires that data that needs to survive the restore operation is logged at\r
+ a location not impacted by the restore so that it can be re-applied to the\r
+ system after its restoration from the backup.\r
+\r
+Downgrade\r
+ The term refers to an upgrade in which an earlier version of the software\r
+ is restored through the upgrade procedure. A system can be downgraded to any\r
+ earlier version and the compatibility of the versions will determine the\r
+ applicable upgrade strategies and whether service outage can be avoided.\r
+ In particular any data conversion needs special attention.\r