# Fusion of Telecommunications and IT Services Boosted by Application Programming Interfaces
## 4 Fusion of Telco and IT Services
### Evolution Path of API Services in Telecommunications
Even though IMS and Internet services have several common features, they differ in some fundamental points, such as access control or business models. To expose telecom abilities to the Internet world, the Telco TM Initiative was born with the emergence of the web. Telco 2.0 offered new telecom business models, and WIMS 2.0 (Web 2.0 & IMS) was proposed as a solution to enable convergence between the mobile world and the web. The exposure of IMS capabilities to the outer world was by Open Web APIs, as described in that paper. In article [1], the authors presented a set of APIs used as part of machine-to-machine communication as a REST-based web service. With the help of these APIs, e.g., it was possible to send SMS/e-mail/Twitter messages to devices registered in the M2M network, showing the early convergence of Telco and IT services already in 2012. As specific use cases, the authors mentioned smart home applications, whereby the subscribers received notifications on their phones about the temperature and light conditions in their homes or when an unauthorized person was intruding, based on inputs from motion sensors. In 2015, [PERSON] et al. [54] reported on two Hackathon events, where new telecommunication-related applications were implemented using a set of Open APIs, combined with datasets provided by Open Data APIs. With the help of APIs provided by a mobile network operator, it was possible to send and receive SMS, MMS, and USSD (Unstructured Supplementary Service Data) notifications, initiate calls, and manage location-, charging-, and SIM card-related data as a REST web service. In addition, detailed maps of several cities (including public transport networks and major institutions, such as hospitals, etc.) could be accessed via an Open Data API. At these two events, an impressive number of more than 100 applications was developed, which also demonstrated the attractiveness of telecommunications services. The Hackathon organizers measured thousands of API calls during the use of the developed applications. The authors also concluded that it is very beneficial to work with interdisciplinary teams during API development, in such a way combining the knowledge of telecommunications and, e.g., the real estate market. In 2019, the authors of [55] outlined a testing framework used for 5G performance and use case testing purposes. In the 5G-VINNI project, it was important to utilize the Open API to access certain elements in the network infrastructure, and this method was also recommended to manage the life cycle of network slices. The project mentioned specific APIs discussed in later articles [56, 57]. According to [8, 17, 58], the Open API concept plays an important role in 5G core networks. The services of different new user groups (called verticals) can be integrated into mobile networks with standard RESTful API calls via the Northbound Interface provided by the Network Exposure Function (NEF). The authors of [4] outlined that the efficient programmability and dynamic shaping of 5G and 6G networks (e.g., management of network slices) are also possible with the invocation of API services, emphasizing the principles of a Software-Defined Network and Network Function Virtualization (NFV). A recent paper from 2021 focused on the security aspect of 5G core networks, emphasizing that the APIs themselves must be protected [59]. This is primarily true in relation to Network Exposure Function, where it is necessary to consider the level of accessibility to the operator's network provided to a third-party through an API [8, 17]. Access has three levels: passive, semi-active, and fully active. At the fully active level, the API developer is authorized to install new network elements within the given network slices. The article also discussed the security risks related to Network Virtualization and Edge Computing; in the latter, the Multi-Access Edge Computing (MEC) cloud-based IT service can also use the Open API, and the authors warn that security risks must also be avoidedat the edge of the network [59; 60; 61].