Page 156 - 5G Basics - Core Network Aspects

1 Core network aspects

I.3 Adaptation to large-scale networks

SDN should provide connectivity from a local area to a wide area, as current networks do. Because SDN
provides logically centralized control of networks, adaptation to large-scale networks is important. A large-
scale network has two aspects: a single SDN domain composed of many network elements, and multiple SDN
domains managed by different network providers. While SDN may support many network elements in a wide
area, the number of network elements that a single SDN controller can accommodate is limited. In this
regard, scalability needs to be considered. One way to provide scalability is to have SDN controllers logically
centralized but physically distributed, to correspond to a wide area.
In large-scale networks, reliability is a particularly important issue. As a characteristic of logically centralized
control in SDN, an SDN controller tends to become a single point of failure. The SDN controller may be
replicated to improve reliability.

I.4 Design of resource abstraction
To make programmability of SDN easier and more efficient, it is important that resource abstraction is
appropriately designed and adopted for the best practice and performance of networks. It is important that
resource abstraction be provided with the following points:
– Common resource abstraction model
It is important that a common resource abstraction model be applied to similar network resources
regardless of the underlying technology, since a common information model simplifies the
programming for the resources. Widely applicable standard information and data models require
the appropriate abstraction of various capabilities, such as packet forwarding, wireless interfaces,
and path computation-related information (e.g., routing metrics).
– Appropriate granularity of abstraction
It is not appropriate to show all network resources and their characteristics to SDN applications. On
one hand, not all the details and characteristics of the network resources are necessary for SDN
application programming. On the other hand, excessive abstraction prevents SDN applications from
utilizing network resources to the maximum because it hides the details of the resources. It is
therefore important that SDN provides an appropriate and balanced granularity of abstraction.
– Performance tuning of network resources
When network resources are abstracted, an SDN application may not be able to access some
network resource-specific parameters, and this may degrade the performance. Suitable abstraction
or some mechanisms to tune the performance of network resources automatically are necessary.

I.5 Virtualization of network elements
Network elements, which can be abstracted resources, may be shared among multiple applications. But each
SDN application does the programming of network elements according to the SDN application requirements.
In that case, it is necessary that these networks and network elements are mutually isolated. Toward this
end, network elements should be virtually partitioned to support each application network.

SDN applications may require network resources, e.g., bandwidth and packet processing, whereas the
applications' requirements cannot be satisfied with a single network element. In that case, multiple network
elements can be virtually combined to appear as a single resource to the applications to satisfy the
requirements without further management efforts of multiple network resources.
For the above two cases, virtualization techniques can provide an appropriate solution because they assume
network element partition and aggregation, as well as a single interface to such virtualized network
resources.

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