# On End-to-End Intelligent Automation of 6G Networks
## 3 5G Orchestration: Related Works and Limitations
### Related Works  
[PERSON] et al. focused on the problem of network service provisioning and orchestration in 5G networks [70]. More specifically, the authors proposed a multi-domain orchestrator (MdoO) prototype based on the 5G exchange (5 GEx) project [70]. The goal is to be able to orchestrate services across multi-domain and multi-technology 5G networks. To that end, the authors built on the functionalities offered by SDN and NFV paradigms to design and implement the 5 GEx-MdoO prototype that is capable of [70]:  
* Discovering other operators' orchestrator and related capabilities/resources;
* Receiving and deploying network services and resource requests from other orchestrators;
* Monitoring the deployed requests/services' performance. Experimental results showed that the proposed prototype is able to deploy new orchestrators in less than two minutes and instantiate new network services and requests in less than 2 s [70]. Similarly, [PERSON] et al. also built on the functionalities of SDN and NFV as part of their 5G network orchestration solution [71]. However, the authors focused on the orchestration of the transport network and radio access network (RAN) [72]. To that end, the authors proposed a hierarchical cross-domain orchestrator that offers network programmability and flexibility. To make the required decisions, the orchestrator monitors the radio resources at the network access edge level, the transport resources at the access and aggregation levels across multiple domains (e.g., optical, packet, and microwave networks), and the cloud resources at the network core level. Experimental results using their testbed showed that the proposed orchestrator improved the service agility and efficiency of resource utilization, particularly in the case of multiple service providers [71]. [PERSON] et al. also addressed the problem of multi-domain multi-technology 5G network orchestration [73]. More specifically, the authors focused on orchestrating 5G crosshaul (integrated fronthaul and backhaul) transport resources with the goal of providing automated, integrated, and flexible 5G network management. To that end, a hierarchical approach that exploited a developed application programming interface (API) was adopted to automate network resource orchestration. Accordingly, the authors deployed a complete 5G crosshaul network instance on a geographically distributed testbed. Experimentalresults showed that the proposed orchestrator was able to set up a complete service in around 10 s. Additionally, it reduced the local service recovery time to around 0.3 s and the centralized service recovery time to around 6.6 s. Hence, the proposed orchestration solution met the 5G network service setup time target of minutes [73]. [PERSON] et al. also adopted an SDN-based approach for 5G network orchestration [74]. The authors focused on integrating edge-centric computing (ECC) and content-centric networking (CCN) paradigms, two promising technologies in 5G networks, into a hierarchical structure titled ECCN [74]. To that end, the authors proposed a heterogeneous RAN architecture that supports both ECC and CCN paradigms. Additionally, the authors designed a specific SDN-based protocol that decoupled the data forwarding and network control of ECC and CCN. Simulation results showed that the proposed ECCN orchestration scheme improved the hit ratio of CCN networks and reduced the amount of redundant traffic sent from the cloud core to the edge devices. As such, more network resources are available for users to request new services and content [74]. On the other hand, [PERSON] et al. focused on the problem of 5G transport network resource orchestration for vertical industries [75]. To that end, the authors proposed an orchestrator architecture that supports the underlying vertical services with the goal of meeting their diverse resource and service requirements.