4 Overview

29.2223GPPCommon API Framework for 3GPP Northbound APIsRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.1 Introduction

In 3GPP, there are multiple northbound API-related specifications. To avoid duplication and inconsistency of approaches between different API specifications and to specify common services (e.g. authorization), 3GPP has considered in 3GPP TS 23.222 [2] the development of a common API framework (CAPIF) that includes common aspects applicable to any northbound service APIs.

The present document specifies the APIs needed to support CAPIF.

4.2 Service Architecture

3GPP TS 23.222 [2], clause 6 specifies the functional entities and domains of the functional model, which is depicted in Figure 4.2-1, in detail.

Figure 4.2-1: CAPIF Functional Model

CAPIF-1 and CAPIF-1e reference points connect an API invoker inside the PLMN Trust Domain and an API invoker outside the PLMN Trust Domain respectively, with the CAPIF core function.

CAPIF-2 and CAPIF-2e reference points connect an API invoker inside the PLMN Trust Domain and an API invoker outside the PLMN Trust Domain respectively, with the API exposing function.

CAPIF-3 reference point connects an API exposing function inside the PLMN Trust Domain with the CAPIF core function.

CAPIF-4 reference point connects an API publishing function inside the PLMN Trust Domain with the CAPIF core function.

CAPIF-5 reference point connects an API management function inside the PLMN Trust Domain with the CAPIF core function.

NOTE: The API exposing function, API publishing function and API management function are part the API provider domain which can be implemented by the Service Capability Exposure Function (SCEF) and/or the Network Exposure Function (NEF).

3GPP TS 23.222 [2], clause 6 specifies functional model for the CAPIF to support 3^rd party API providers, which is depicted in Figure 4.2-2 in detail

Figure 4.2-2: Functional model for the CAPIF to support 3rd party API providers

The CAPIF core function in the PLMN trust domain supports service APIs from both the PLMN trust domain and the 3rd party trust domain having business relationship with PLMN Trust Domain. The API invokers may exist within the PLMN trust domain, or within the 3rd party trust domain or outside of both the PLMN trust domain and the 3rd party trust domain.

CAPIF-3e reference point connects an API exposing function outside PLMN Trust Domain with the CAPIF core function.

CAPIF-4e reference point connects an API publishing function outside PLMN Trust Domain with the CAPIF core function.

CAPIF-5e reference point connects an API management function outside PLMN Trust Domain with the CAPIF core function.

CAPIF-7 and CAPIF-7e reference points connect API exposing functions within PLMN Trust Domain and outside PLMN Trust Domains respectively. 3GPP TS 23.222 [2] specifies functional model for interactions between API exposing functions.

NOTE: CAPIF-7 reference point is not represented in the Figure 4.2-2 which is aligning to TS 23.222 [2].

3GPP TS 23.222 [2], clause 6 specifies functional model to support CAPIF interconnection, which is depicted in Figure 4.2-3 in detail.

Figure 4.2-3: CAPIF interconnection functional model

CAPIF-6 and CAPIF-6e reference points connect two CAPIF core functions located in the same or different PLMN trust domains, respectively. The reference points allows API invokers of a CAPIF provider to utilize the service APIs from the 3rd party CAPIF provider or another CAPIF provider within trust domain.

4.3 Functional Entities

4.3.1 API invoker

The API invoker is typically provided by a 3^rd party application provider who has service agreement with PLMN operator. The API invoker may reside within the same trust domain as the PLMN operator network.

The API invoker supports several capabilities such as supporting

– the authentication and obtaining authorization and discovering using CAPIF-1/CAPIF-1e reference point as defined in 3GPP TS 23.222 [2]; and

– invoking the Service APIs using CAPIF-2/CAPIF-2e referenced point as defined in 3GPP TS 23.222 [2], e.g. the T8 interface as defined in 3GPP TS 29.122 [14] or the NEF Northbound interface as defined in 3GPP TS 29.522 [15].

4.3.2 CAPIF core function

The CAPIF core function (CCF) supports the following capabilities over CAPIF-1/CAPIF-1e reference point as defined in 3GPP TS 23.222 [2]:

– authenticating the API invoker;

– providing the authorization information; and

– service API discovery.

The CAPIF core function supports the following capabilities over CAPIF-3 and CAPIF-3e reference points as defined in 3GPP TS 23.222 [2]:

– providing the service API access policy;

– providing the authentication and authorization information of API invoker for validation;

– providing API routing information;

– providing API topology hiding information;

– logging of service API invocations; and

– charging of service API invocations.

The CAPIF core function supports the following capabilities over CAPIF-4 and CAPIF-4e reference points as defined in 3GPP TS 23.222 [2]:

– publishing and storing the service APIs information.

The CAPIF core function supports the following capabilities over CAPIF-5 and CAPIF-5e reference points as defined in 3GPP TS 23.222 [2]:

– providing the service API invocation log for auditing;

– providing monitoring information the status of service APIs and

– storing configurations of the API provider policies.

– registering of API provider domain functions.

– update registration information of API provider domain functions.

The CAPIF core function supports the following capabilities over CAPIF-6 and CAPIF-6e reference point as defined in 3GPP TS 23.222 [2]:

– publishing of service APIs information with another CAPIF core function; and

– discovery of service APIs information with another CAPIF core function.

4.3.3 API exposing function

The API exposing function (AEF) is the provider of the Service APIs and is also the service communication entry point of the Service API to the API invokers using CAPIF-2/CAPIF-2e reference point as defined in 3GPP TS 23.222 [2]. The API exposing function consists of capabilities such as authenticating the API invoker, validating the authorization provided by the CAPIF core function and logging the Service API invocations at the CAPIF core function using CAPIF-3 and CAPIF-3e reference points as defined in 3GPP TS 23.222 [2].

According to the distributed deployment scenarios specified in 3GPP TS 23.222 [2], it is possible that the CAPIF can be deployed by splitting the functionality of the API exposing function among multiple API exposing function entities, of which one acts as the entry point. The source API exposing function communicates with the destination API exposing function over CAPIF-7/7e reference points.

4.3.4 API publishing function

The API publishing function (APF) enables the API provider to publish the Service APIs information using CAPIF-4 and CAPIF-4e reference points as defined in 3GPP TS 23.222 [2] in order to enable the discovery of Service APIs by the API invoker.

4.3.5 API management function

The API management function (AMF) enables the API provider to perform administration of the Service APIs. The API management function supports several capabilities such as querying the Service API invocation log for auditing, monitoring the events, configuring the API provider policies and monitoring the status of the Service APIs, register and maintain registration information of the API provider domain functions on the CAPIF core function, using CAPIF-5 and CAPIF-5e reference points as defined in 3GPP TS 23.222 [2].