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Core network aspects 1

to each SDN application. The AL-MSO functional component obtains resource quality of service information
in order to measure and record key performance indicators (KPIs) for the SDN applications. Computing and
storage resources required for executing an SDN application are allocated or de-allocated based on these
KPIs. In case virtual networks have been created, they are built with the support of the SDN-CL, and may use
the same application layer, or attach an SDN-AL instance to each virtual network.

7.2 SDN control layer

The SDN-CL provides programmable means to control the behaviour of SDN-RL resources (such as data
transport and processing), following requests received from the SDN-AL and according to MMF policies. The
SDN-CL is operating on resources provided by the SDN-RL and exposes an abstracted view of the controlled
network to the SDN-AL.
The SDN-CL interacts with the SDN-RL using the resource control interfaces (RCI) reference point, and with
MMF using the MMF control layer (MMFC) reference point. It also interacts with the SDN-AL at the ACI
reference point, as described in clause 7.1.

Figure 7-3 shows the SDN-CL functional components.

Figure 7-3 – SDN-CL functional components

7.2.1 CL application support functional component
The control layer application support (CL-AS) functional component provides an ACI reference point that is
used by the SDN-AL to access network information and to request the SDN-CL to perform application-specific
behaviour. The information exposed by the CL-AS functional component to the SDN-AL is abstracted by
means of information and data models. In case of network virtualization, the CL-AS functional component
may expose a subset of network resources which can be used for exclusive control by additional, external
SDN control and application layers. Specification of such operations is out of scope of this Recommendation.

NOTE – The control layer resource abstraction (CL-RA) functional component of the SDN-CL hides the configuration and
technology-specific details of potentially heterogeneous network elements whereas the CL-AS functional component
hides details of the underlying network topology by providing a global and abstracted view of that network.
7.2.2 Control layer management support and orchestration functional component

The control layer (CL) management support and orchestration (CL-MSO) functional component provides
management support and orchestration of functional components of the SDN-CL and, if delegated by the
MMF, the management and orchestration of network resources based on the policies provided by the MMF.
The CL-MSO functional component provides capabilities for provisioning CL services, both in terms of the
provisioning of CL services' implementations and of their access endpoints and the workflow required to
ensure that CL services' components are provisioned in the correct sequence. A catalogue of CL services
provides a list of all available CL services that can be provisioned by the CL-MSO functional component. This

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