# A Survey on Open Radio Access Networks: Challenges, Research Directions, and Open Source Approaches
## 6 Challenges and Future Research Directions
### Open RAN Field Issues
Different vendors will use a wide range of components. It would be difficult to establish the location of bottlenecks that reduce the overall performance while using the heterogeneous components. In addition to the multiple vendor challenge, the requirement that Open RAN should also be able to interact with legacy 4G equipment will rocket the challenge even higher. Some questions are also raised regarding the multivendor environment in Open RAN. When the RAN experiences a problem, how do MNOs decide which vendor should solve it? What is needed and how the operator decides in a multivendor environment remain open. There is also a concern about whether MNOs should directly deploy multivendor Open RAN or start working with a single vendor before reorganizing the supply chain to a multivendor environment at a future stage. Survey shows that about 40% MNOs expect to work with only one to-two established vendors at the beginning [88]. Integration challenge is the next issue relating to Open RAN implementation. Ericsson mentioned that it concerned Open RAN's hardware integration [16]. With the complex multivendor ecosystem Open RAN offers, MNOs ranked integration issues as the second major obstacle with a 55% vote [89]. We know that openness has become a fundamental pillar of Open RAN from the very start [15], where in an OpenRAN architecture, hardware and software come from many different vendors, thus making it a multivendor architecture. Because the architecture involves components from different vendors, every service provider and mobile operator has to ensure that their networks continue to operate smoothly with all these different parties in their network [16]. There are four different Open RAN system integration models to tackle this challenge [16]. In the first model, MNO will do the integration, just like Rakuten and Vodafone did. However, this approach requires the MNO to possess great in-house expertise. Integration will be carried out by the service provider in the second model. This model would perform well if the service providers have extensive experience working with multiple resources. The third model assigns the integration role to the hardware or software vendor. Fujitsu shows an example of this, providing support in RU to DU integration for Dish [16]. Even so, it would be a challenge to ask vendors to integrate on behalf of their competitors [16]. The use of a service from a system integrator, a new actor, is the last model. The system integrator is a third party not associated with a certain hardware or software vendor, yet that works closely with the vendors to ensure their heterogeneous products work together [16]. Telefonica has provided an example by using services from Everis, a Spanish system integrator [16]. The appearance of this new role opens fresh business opportunities for companies who want to join the ecosystem. NEC, currently the most engaged system integrator, and others have sensibly taken this opportunity [90]. The RAN needs a new approach to guarantee that all MNOs can operate their networks smoothly in an Open RAN. This approach should prioritize a software-driven and open-minded ecosystem from hardware vendors, software vendors, system integrators, tower companies, real estate owners, regulators, industry bodies, and MNOs. The integration of Open RAN needs to be built for a software-centric world. In this software-centric world, each software talks to all physical components to deliver scalability and innovation and change how open networks are integrated. This approach will be mostly focused on Open RAN software, where the software will make those components smarter and interoperable. This approach will also help those components be integrated and maintained remotely by using a software upgrade, so MNOs and vendors no longer need to climb network towers. To integrate Open RAN, two levels of integration need to be carried out: Open RAN ecosystem integration and Open RAN software system integration.