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diff --git a/docs/requirements/usecase.rst b/docs/requirements/usecase.rst deleted file mode 100644 index bdf8888..0000000 --- a/docs/requirements/usecase.rst +++ /dev/null @@ -1,121 +0,0 @@ -.. This work is licensed under a Creative Commons Attribution 4.0 International License. -.. http://creativecommons.org/licenses/by/4.0 - -======================= -Use cases and scenarios -======================= - -Use cases -========= - -Resource reservation is a basic feature in any virtualization-based network -operation. In order to perform such resource reservation from NFVO to VIM, NFVI -capacity information is also necessary at the NFVO side. Below, four use cases -to show typical requirements and solutions for capacity management and resource -reservation is presented. A typical use case as considered for the Brahmaputra -release is described in :ref:`uc-brahmaputra`. - -#. Resource capacity management -#. Resource reservation for immediate use -#. Resource reservation for future use -#. Co-existence of reservations and allocation requests without reservation - -Resource capacity management ----------------------------- - -NFVO takes the first decision on in which NFVI it would instantiate a VNF. Along -with NFVIs resource attributes (e.g. availability of hardware accelerators, -particular CPU architectures etc.), NFVO needs to know available capacity of an -NFVI in order to make an informed decision on selecting a particular NFVI. Such -capacity information shall be in a coarser granularity than the respective VIM, -as VIM maintains capacity information of its NFVI in fine details. However a -very coarse granularity, like simply the number of available virtual CPU cores, -may not be sufficient. In order to allow the NFVO to make well founded -allocation decisions, an appropriate level to expose the available capacity may -be per flavor. Capacity information may be required for the complete NFVI, or -per partition or availability zone, or other granularities. Therefore, VIM -requires to inform the NFVO about available capacity information regarding its -NFVI at a pre-determined abstraction, either by a query-response, or in an -event-based, or in a periodical way. - -Resource reservation for immediate use --------------------------------------- - -Reservation is inherently for the future. Even if some reserved resources are to -be consumed instantly, there is a network latency between the issuance of a -resource reservation request from the NFVO, a response from the VIM, and actual -allocation of the requested resources to a VNF/VNFM. Within such latency, -resource capacity in the NFVI in question could change, e.g., due to failure, -allocation to a different request. Therefore, the response from a VIM to the -NFVO to a resource reservation request for immediate use should have a validity -period which shows until when this VIM can hold the requested resources. During -this time, the NFVO should proceed to allocation if it wishes to consume the -reserved requested. If allocation is not performed within the validity period, -the response from VIM for a particular resource reservation request becomes -invalid and VIM is not liable to provide those resources to NFVO/VNFM anymore. -Reservations requests for immediate use do not have a start time but may have -an end time. - -Resource reservation for future use ------------------------------------ - -Network operators may want to reserve extra resources for future use. Such -necessity could arise from predicted congestion in telecom nodes e.g. due to -local traffic spikes for concerts, natural disasters etc. In such a case, the -NFVO, while sending a resource reservation request to the VIM, shall include a -start time (and an end time if necessary). The start time indicates at what -time the reserved resource shall be available to a designated consumer e.g. a -VNF/VNFM. Here, the requirement is that the reserved resources shall be -available when the start time arrives. After the start time has arrived, the -reserved resources are allocated to the designated consumer(s). An explicit -allocation request is needed. How actually these requested resources are held -by the VIM for the period in between the arrival of the resource reservation -request and the actual allocation is outside the scope of this requirement -project. - -Co-existence of reservations and allocation requests without reservation ------------------------------------------------------------------------- - -In a real environment VIM will have to handle allocation requests without any -time reference, i.e. time-unbound, together with time-bound reservations and -allocation requests with an explicitly indicated end-time. A granted -reservation for the future will effectively reduce the available capacity for -any new time-unbound allocation request. The consequence is that reservations, -even those far in the future, may result in denial of service for new -allocation requests. - -To alleviate this problem several approaches can be taken. They imply an -implicit or explicit priority scheme: - -* Allocation requests without reservation and which are time-unbound will be - granted resources in a best-effort way: if there is instant capacity, but the - resources may be later withdrawn due to the start time of a previously - granted reservation -* Both allocation requests and reservation requests contain a priority which - may be related to SLAs and contractual conditions between the tenant and the - NFVI provider. Interactions may look like: - - * A reservation request for future use may cancel another, not yet - started, reservation with lower priority - * An allocation request without reservations and time-unbound [#unbound]_ - may be granted resources and prevent a future reservation with lower - priority from getting resources at start time - * A reservation request may result in terminating resources allocated to a - request with no reservation, if the latter has lower priority - -.. [#unbound] In this case, the consumer (VNFM or NFVO) requests to immediately - instantiate and assign virtualized resources without having - reserved the resources beforehand - -Scenarios -========= - -This section describes the expected behavior of the system in different -scenarios. - -As we are targeting a cloud platform with the above use cases, it is crucial to -keep the flexibility in the system. By this means it is hard to explicitely -block hardware resources for the future and ensure their availablility for -allocation therefore it can happen that the reservation plan cannot be fulfilled -due to certain changes in the underlying environment. We need to ensure that we -are prepared for error and edge cases during the design period. |