Page 176 - ITU-T Focus Group IMT-2020 Deliverables

3 ITU-T Focus Group IMT-2020 Deliverables

Although there could be some gains to use these technologies in some portion of the network, it is important
that corresponding control plane mechanisms are necessary to efficiently integrate and coordinate this kind
of technologies in the whole transport network.
8.2.6.2 Control plane for guaranteed bandwidth

5G network will provide diversified services on the same physical infrastructure, some of these services
require strict bandwidth guarantee, while some others have flexible bandwidth requirement and can adapt
via statistical multiplexing. It will be a challenge for existing transport networks to meet the bandwidth
requirements for both kinds of services simultaneously.
Some technologies such as FlexE can provide guaranteed bandwidth on an Ethernet data link for a specific
service. However in order to achieve the bandwidth guarantee on the end-to-end transport network, some
additional control plane mechanisms are needed.
8.2.6.3 Control plane for very large scale network

Widespread deployment of small-size cells is required to support high-speed and large-capacity mobile
communications. For instance, assuming that a macro cell of 2km radius is replaced with small cells of 200m
radius, the number of cells calculated based on the surface area would increase 100 times. As a result the
scale of the transport networks need to increase accordingly. The control planes must also be sufficiently
scalable for such large scale transport network. It is anticipated that neither totally centralized control nor
completely distributed control could meet such requirement, thus a hybrid control mode should be
considered. Enhancements to both the existing distributed protocols and the centralized SDN mechanisms
would be needed, and the control plane would make use of the advantages of both approaches.
8.2.6.4 Control plane for flexible connectivity and topology

With the evolution of distributed mobile Core, and the introduction of C-RAN and MEC, 5G services will have
diversified connectivity requirements. The connections will not only be between the RF sites and the
centralized mobile core, but would also include various connectivity among the RF sites, C-RAN, MEC, the
distributed Core (or edge located Core) and other DCs. This requires the transport network to provide flexible
connectivity among all these entities. In addition, since network slicing will be used to provide dedicated
slices for different services, in each slice it is necessary to provide specific service with the customized
network topology. Potential control plane mechanisms need to be investigated to establish the customized
network topologies and set up the required connections in a flexible manner.

8.2.6.5 Control plane for flexible resources assignment and sharing

With the network slicing mechanism, when a virtual or physical network slice is created, the control plane
should be used to dynamically assign the required resources for the slice on the physical network. Since
different market segments and verticals such as mobile broadband, MVNO and various IoT services will use
different network slices, the control plane needs to support flexible resource assignment to meet diverse
resource requirements. Typically the network resources assigned to network slices can belong to two
categories: dedicated or shared. Dedicated resources can only be consumed by the assigned slice, and should
be isolated with other slices, while the shared resources can be shared among several slices. Control plane
should provide mechanisms to support both resource isolation and sharing.

In addition, when a dedicated resource has been allocated to a slice, a mechanism must exist so that the
actual resource usage can be monitored and can grow or shrink as required. In this manner the control plane
could provide a slow adaptive method to allow resources to move from slice to slice without having to use
statistical multiplexing. Ideally this should be done in a make-before-break manner.

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