The term refers to making a copy of the system persistent data to a storage, so that it can be used to restore the system or a given part of it to the same state as it was when the backup was created. Restoring from backup will lose volatile states like CPU and memory content. Changes made to the system from the moment the backup was created to the moment it is used to restore the (sub)system are also lost in the restoration process.
The term refers to an upgrade operation in which an earlier version of the software is restored through the upgrade procedure. Compared to rollback, Downgrade is normally initiated with Operator, and it is allowed to select any earlier version, providing the compatibility of the versions is met or upgrade strategies are allowed (whether service outage or data lost can be tolerant.)
The term refers to a subscriber of the Operator’s services.
High Availability(HA)
High Availability refers to a system or component that is continuously operational for a desirably long length of time even a part of it is out of service. HA system is popular in Operator’s data center for critical tasks. Non-HA system is normally deployed for experimental or in-critical tasks in favor of its simplicity.
Infrastructure Services
The term refers to services provided by the NFV Infrastructure to the VNFs as required by the Management & Orchestration functions and especially the VIM. I.e. these are the virtual resources as perceived by the VNFs.
Infrastructure Resource Model
The term refers to the representation of infrastructure resources, namely: the physical resources, the virtualization facility resources and the virtual resources.
Network Service
The term refers to a service provided by an Operator to its end-users using a set of (virtualized) Network Functions
The term refers to network service providers and Virtual Network Function (VNF) providers.
The terms refers to the period of time when a given service is not available to End-Users.
Parallel Universe Upgrade
The term refers to an upgrade strategy, which creates and deploys a new universe - a system with the new configuration - while the old system continues running. The state of the old system is transferred to the new system after sufficient testing of the new system.
Physical Resource
The term refers to a piece of hardware in the NFV infrastructure that may also include firmware enabling this piece of hardware.
The term refers to a failure handling strategy that reverts the changes done, for example, by an upgrade by restoring the system from some backup data. This results in the loss of any change and data persisted after the backup was been taken. To recover those additional measures need to be taken if necessary (e.g. Rollforward).
The term refers to a failure handling strategy that reverts the changes done by a potentially failed upgrade execution one by one in a reverse order. I.e. it is like undoing the changes done by the upgrade.
The term refers to a failure handling strategy applied after a restore (from a backup) operation to recover any loss of data persisted between the time the backup has been taken and the moment it is restored. Rollforward requires that data that needs to survive the restore operation is logged at a location not impacted by the restore so that it can be re-applied to the system after its restoration from the backup.
Rolling Upgrade
The term refers to an upgrade strategy, which upgrades a node or a subset of nodes at a time in a wave style rolling through the data centre. It is a popular upgrade strategy to maintain service availability.
Smooth Upgrade
The term refers to an upgrade that results in no service outage for the end-users.
The term refer to the state of a system at a particular point in time, or the action of capturing such a state.
Upgrade Campaign
The term refers to a choreography that describes how the upgrade should be performed in terms of its targets (i.e. upgrade objects), the steps/actions required of upgrading each, and the coordination of these steps so that service availability can be maintained. It is an input to an upgrade tool (Escalator) to carry out the upgrade.
Upgrade Duration
The duration of an upgrade characterized by the time elapsed between its initiation and its completion. E.g. from the moment the execution of an upgrade campaign has started until it has been committed. Depending on the upgrade strategy, the state of the configuration and the upgrade target some parts of the system may be in a more vulnerable state with respect to service availability.
Virtualization Facility
The term refers to a resource that enables the creation of virtual environments on top of the physical resources, e.g. hypervisor, OpenStack, etc.
Virtual Resource
The term refers to a resource, which is provided as services built on top of the physical resources via the virtualization facilities; in particular, virtual resources are the resources on which VNFs are deployed. Examples of virtual resources are: VMs, virtual switches, virtual routers, virtual disks.


The term is an abbreviation for Network Function Virtualization Infrastructure; sometimes it is also referred as data plane in this document. The NFVI provides the virtual resources to the virtual network functions under the control of the VIM.
The term is an abbreviation for Virtual Infrastructure Manager; sometimes it is also referred as control plane in this document. The VIM controls and manages the NFVI compute, network and storage resources to provide the required virtual resources to the VNFs.