Setup Multiple DUs with 1 CU

[hpate063]

Hi,

I am wondering if I can setup multiple DUs (all connected to one CU). I see mentions of using cell configurations to do this but I am wondering if there is any documentation which explains how to set this up clearly. If so, can someone please share? If not, can someone share any guidelines?
(Note: It is okay if UE can not handover between the 2 cells)

Further, can I connect these different DUs to the same RU (USRP) or do I need different RUs?

[pgawlowicz]

you can check our HO tutorial: https://docs.srsran.com/projects/project/en/latest/tutorials/source/handover/source/index.html

[hpate063]

Thanks. This is helpful.

[s21sm]

Hi @pgawlowicz ,
Thanks for the HO tutorial. I followed the given instruction. My connection with COTS UE is ok, I can browse the Internet. I changed tx / rx gain, UE physical location, but hand over never triggered. The problem that I am facing is if I put a3_report_type: rsrp in the configuration file, gNB can not parse it, says INI was not able to parse a3_report_type. In srsRAN code I found they are using event_triggered_report_type: a3. I used that, and gNB parsed that. Here is my configuration file and gNB output.

x310.txt
gNB.txt

Kindly help!

[pgawlowicz]

There was a change in the configuration structure. We are currently updating the docs. Please check here: https://github.com/srsran/srsRAN_Project/blob/main/configs/mobility.yml

[frankist]

@hpate063, I got a bit confused by your question. I understood that you want to work with a CU/DU split instead of a monolithic gNB (CU and DU co-located) and you want to have 2 or more DUs connected to a single CU, correct? If that's the case, you cannot share one RU across multiple DUs. Each DU has its own RU. From the perspective of the connection between the DUs and the CU (F1 interface), the main thing you have to ensure is that the F1 bind IP address of the DUs does not collide if they are in the same machine, and that the DUs have different gnb_du_id and pci values. This is very easy to ensure this via the config file.

[hpate063]

Yes, correct. So two things here:

1. Ensure connection between DUs and CU: I can do that via config and that seems good.
2. Connection between RU and DU: If an RU can not be shared across DUs, this is where I would like to inquire further.

I want to have a system where 1 RU can be connected to multiple DUs. It is okay if it is 1 DU divided into 2 logical DUs or 2 separate DUs. The aim is to serve a UE via the RU-DU1-CU and move it's service to the RU-DU2-CU (while the session is active).
I am thinking of implementing a module (possibly between the OFH and DU-low) to accomplish this. Another idea I am thinking of is to duplicate the creation of DU in software and manage states to realize the necessary functionality.

I understand that my question is a bit abstract but I would like to understand the feasibility of either option and avoid one or the other in case the srsRAN architecture does not allow me. Can you tell me what option is feasible? Or if there an another way you suggest I can design?

[frankist]

If you do not have the requirement that the two DUs are in separate machines, what you are asking should be possible. We already support "RU-DU1-CU + RU-DU2-CU" when using the monolithic gNB app. You just need to increase the number of cells to 2 and the RU will treat the 2nd DU as an extra cell of a single DU. I don't see any conceptual impediment to do the same with the split CU/DU. The standalone DU app could also contain an "RU-DU1 + RU-DU2".

I have to be honest though that I've not tested this yet, so I will have a look next week.

[hpate063]

That is great to hear. I will try to set it up as well and see what are the challenges.

Thanks again and looking forward to your update.

[hpate063]

@frankist Were you able to test this setup? Can you provide me any guidelines on the same?

[Urojtariq]

Hi @hpate063
I am also trying to make two DUs(connected to single CU), in the same machine. and I have tried all the optione mentioned above, but my USRP(single) does not seems to connect with two DUs, I want to make sure that I am creating 2 DUs in the right format. Did you get any success in that, and Can you provide me with the guidelines.

[s21sm]

@Urojtariq quick question, what is your USRP model?

[ulopezindra]

Hi,
I'm trying to use 1 CU along with 2 DUs and 2 RUs. Is this possible? Could you provide me with some guidance on how to do it?

                             DU - RU ----- UE    
                          /      
 CORE ----CU -
                          \ 
                             DU - RU ----- UE

[natthapolpetch]

This git #1256 try to do what you are looking for. Please see how to setup for a CU and both DUs here.
I am also doing this CU-DU split setup with 2 bladeRFs as RU connected to separate DU (DU1 and DU2), and one CU.