Page 54 - ITU-T Focus Group IMT-2020 Deliverables

2 ITU-T Focus Group IMT-2020 Deliverables

and the access type used. And functional entities are likely to be distributed on-demand basis over the
infrastructure. Therefore, in the IMT-2020 architectures, there shall be a clear decoupling of service, network,
and infrastructure, allowing them to be offered separately and to evolve independently. The separation is
represented by three strata in the figure.

In general, each stratum will have its own set of roles, players and administrative domains (refer to
[b-ITU-T Y.110]). The roles involved in service(s) provision are independent from those involved in network
connectivity provision. Each stratum needs to be treated separately from a technical point of view. In the
figure, Multi-domain orchestration refers to the automated management of services and resources in multi-
technology (multiple domains involving different cloud and networking technology) and multi-operator
(multiple administrative domains) environments [b-ITU-T IMT-O-047].

I.1.1.1 IMT-2020 network stratum
By virtue of softwarization and pervasive deployment of computing infrastructure, network function
instances can be distributed on-demand basis. This brings IMT-2020 network architecture a shift in
networking paradigms: a transition from deployment of network entities with fixed functionalities
(e.g., PGW, SGW, etc.) to deployment of network functions as necessary.

IMT-2020 network stratum provides network services requested by service stratum using network functions
instantiated at right place. IMT-2020 infrastructure stratum provides required infrastructure resources to
instantiate the network functions.

The functional architecture of IMT-2020 network stratum shall provide a complete set of network functions
required to support all IMT-2020 services. Reference points and information flows between interacting
functions will be defined in the architecture, too. As new services emerge in the future, interconnection
model between network functions needs to allow easy insertion of new network functions while maintaining
the existing network function interconnection path without increasing complexity of the system.

Network operators can provision and operate many different network slices according to their business
strategies. A network slice is comprised of only necessary network functions. They are collected from a
complete set of network functions in the IMT-2020 network functional architecture, and orchestrated for the
particular service and purpose.
Life cycle management including orchestration and instantiation of network slices is performed by
management plane network functions (e.g., NSMF). Management plane is also responsible for the life cycle
management of network functions.
Network functions in control plane and user plane operate on instantiated network slices, i.e. network slice
instances. Fundamental control plane network functions include ANCF (Access Network Control Function),
NSCF (Network Slice Control Function), MMCF (Mobility Management Control Function), SMCF (Session
Management Control Function), PCRF (Policy and Charging Rule Function), and AAAF (Authentication
Function), etc.
Figure 5-3 shows IMT-2020 network architecture framework. High level functional architecture of IMT-2020
is defined in clause 6. Each network function is comprised of one or more functional entities.

48