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:

  1. 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.
  2. 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.
  3. 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

One thought on “Open RAN with Bullets – Part 2”

Leave a Reply

Your email address will not be published. Required fields are marked *