Even though I have already described high level of O-RAN defined Open RAN architecture in the previous post, now I want to give a bit more details about the architecture options including bundling RAN domain elements in terms of O1 and E2 interfaces.
Above illustration depicts:
- External application server which connects to Non-Real Time RIC. Either it can be V2X Server or UAV Server, it depends on the use case. Usually, enrichment information is obtained from the server to use in AI/ML model tuning.
- Even though here it is shown as different cloud infrastructure for each element of RAN domain, it is also possible to be on the same physical resources. So, O-CU, O-DU can be hosted on the same cloud environment. Consequently, it depends on deployment strategy of the service providers.
- We can see RAN protocol stack functional split between elements. Example SDAP is hosted by O-CU-UP and RLC, MAC are hosted by O-DU. General idea of the RAN functional split comes from the 3GPP and it has multiple suggestions (Option 1, Option 2, Option 3 etc.). But the O-RAN Alliance obtained Option 7 and Option 2 and specified it in Open RAN.
Which functional split to be used depends on service deployment scenarios such as URLLC, but O-RAN Alliance supports most optimal one as depicted above.
4. Even though 5G Core network is not mandatory to be presented while explaining the Open RAN, but I think it would be better if we can see big picture like connection of O-CU UP with UPF which carries user plane traffic and O-CU CP with AMF which carries control plane traffic.
Open RAN Elements Bundling Options
Although O-RAN specified elements in Open RAN architecture as different nodes and individual E2 and O1 connections to those elements:
- Near-Real Time RIC
- O – CU – CP
- O – CU – UP
- O – DU
- O – RU
It is also possible to bundle these nodes in different deployments options (so far it is specified 7 options by O-RAN), and in this case O1 and E2 interfaces will be connected to the bundle (as group) and manage them as single element.
- Aggregation O-CU-CP and O-CU-UP
- Aggregation Near-RT RIC, O-CU-CP and O-CU-UP
Click on image to enlarge
- Aggregation O-CU-CP, O-CU-UP and O-DU
- Aggregation O-CU-CP, O-CU-UP, O-DU and O-RU
Click on image to enlarge
- Aggregation O-DU and O-RU
- Aggregation Near-RT RIC, O-CU-CP, O-CU-UP, O-DU and O-RU
Click on image to enlarge
References:
- Toward Next Generation Open Radio Access – IEEE Network Magazine 2022
- O-RAN-Architecture-Description, Technical Specification
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