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My friend: Hi Ibrahim, I have a question for you.
- Me: Please, go ahead.
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My friend: I was wondering if the Open RAN architecture has more interfaces than legacy RAN or not?
- Me: As long as, open RAN added new functionalities more than the legacy RAN, so we should expect to see more interfaces coming to the open RAN architecture. Thus, in open RAN, we have additional interfaces such as A1, E2, O1, O2, and open Fronthaul interfaces. Of course, all these interfaces are open interfaces to allow multi-vendor communication.
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My friend: So, what are the functions of these new interfaces?
- Me: Let’s start with A1 interface which is between the non-RT RIC and the near-RT RIC. So, A1 interface will allow the non-RT RIC to send the policy-based guidance, ML model management and enrichment information to the near-RT RIC to better optimize the RAN performance and at the same time will allow the near-RT RIC to provide policy feedback towards the non-RT RIC, so the non-RT RIC can monitor the usage of the policies sent from his side. And take care that these policies can be for individual UEs or a group of UEs. Also, O2 interface is used between the SMO and the O-cloud to manage the cloud infrastructure resources and deployment operations with O-Cloud infrastructure that hosts the open RAN functions in the network.
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My friend: Ok, what about the other interfaces?
- Me: E2 interface is used between the near-RT RIC and an E2 node (such as O-CU-CP, O-CU-UP, O-DU, and O-eNB), so the near-RT RIC can be connected to multiple E2 Nodes. Also, the E2 interface allows the exposure of selected E2 Node data (e.g., cell configuration, supported slices, network measurements, context information, etc.) towards the near-RT RIC and will enable the near-RT RIC to control and optimize the E2 nodes and the resources they use. Furthermore, note that the protocols that go over the E2 interface are only control plane protocols as simply all the user plane data will go to the core network.
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My friend: But what about the O1 and open Fronthaul interfaces?
- Me: O1 interface is used between the SMO and the RAN managed elements such as near-RT RIC, O-CU-UP, O-CU-CP, O-DU, and O-eNB. So, the management and orchestration functions are sent from the SMO towards the RAN managed elements via the O1 interface and The SMO in turn receives data from the RAN managed elements via the O1 interface for AI model training. While open Fronthaul interface is between the O-DU and O-RU which includes the CUS (Control, User, and Synchronization) plane, while the M (Management) plane will use the Open Fronthaul M-plane interface in case of hierarchical or hybrid modes, also in case hybrid mode is used, then O-RU is controlled from O-DU as mentioned above and also from SMO using the Open Fronthaul M-plane interface as well.
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My friend: Thank you so much. You made it very clear.
- Me: You are most welcome.
LinkedIn: Ibrahim Sayed, PMP on LinkedIn: #5g #openran #oran