Page 85 - ITU-T Focus Group IMT-2020 Deliverables

ITU-T Focus Group IMT-2020 Deliverables 3

6.1.1.2.2 Key issue: Network function granularity and interactions between them

A network generation operator’s network is expected to consist of multiple physical and/or virtual network
functions to support diverse service requirements. To achieve flexibility on that network environment, the
next generation system capabilities should be supported such as dynamic deployment of network functions
and function re-usability based on the architecture principles that principles that allow flexible network
function deployment, ease of interfacing, flexible chaining, co-location of network functions.

Please refer to Clauses 5.7 and 6.7 in NextGen TR 23.799 for the detailed non-exhaustive list of solutions for
this key issue.

Table 6.1.1-2 – Work tasks for interconnection NF

Work Task ID Work Task(s) Work Task Description
INF_WT_#1 Network function 1. State assumption and/or applicability of the proposed reference
interconnection model
reference model 2. Depict how the network functions are connected using the
proposed reference model
3. Identifying a mechanism for a NF instance to interconnect to its
peer NFs instances (e.g., via provisioning, selection and discovery
etc.)
INF_WT_#2 Sample call flow 1. Describe sample call flows, e.g. network function A sending a
req/rsp to network function B

Interim agreements for Key issue #7 “Function Granularity and Interconnection of them” are as follows:
1) Any two NFs interacts with each other directly while avoiding the functional and signalling impact
on unrelated NF.
NOTE 1 – This does not preclude to pass information via a third NF if two NFs do not interact directly, e.g. if
MM received subscription information from SDB then it can pass it to SM if there is an interaction between
MM and SM (e.g., during PDU connection establishment procedure).
2) In order to facilitate utilization of the capability (s) of one NF the capability (s) of NFs are exposed as
a service to other NF, wherever applicable, (e.g., by following the guidelines defined in Annex E). As
such the NF provides a service based interface to other NFs.
NOTE 2 – It is expected that SA2 will specify the end to end signalling flow and then deduce the services and
functionalities that one NF supports, and CT WGs define the data model of service interface, i.e. information
elements included in service interface. For more detail refer to Annex X.
NOTE 3 – To support different variants of a service and to enable the invoking NF to discover the expected
service, the service need be uniquely identified.
3) Network functions within the NG Control plane unless determined otherwise during the normative
phase, shall exhibit service based interfaces for services that can be re-used by multiple network
functions. This will be evaluated on a case by case basis when specifying the procedure. The NG1,
NG2, NG4 interface are not considered to support the service based interface.
4) The NF selection and discovery shall be supported to enable NF selection and discovery, including:
– The NF selection and discovery function maintains the function profile of the deployed NF
instances, e.g. the type of the NF, network slice related information which the NF belongs to.
– When deploying/removing one NF instance, the information of the NF instance is updated.
– One NF shall be able to utilize the type of the NF (e.g., SMF, PCF, etc.)and other service
parameters (including network slice related parameters) to discover the expected NF instance
(s), and the NF selection and discovery function provides the IP address or the FQDN of NF
instance(s) to the NF.
NOTE 4 – The network slice related information/parameters are determined in the key issue #1.

79