multi UEs+ZeroMQ+multi gnbs +open5gs

[wmwwimor]

I would like to know if it is possible to implement this architecture:multi UEs+ZeroMQ+one gnb +open5gs. Can it currently be achieved using GNU Radio? Is it possible to further expand it into such an architecture:multi UEs+ZeroMQ+multi gnbs +open5gs? I don't want to use physical devices. Is there something similar to ZeroMQ available now that can assist in simulating radio frequencies?

[brendan-mcauliffe]

See answer to the same question here: srsran/srsRAN_4G#1203 (comment)

[jonniebeeb]

Can I ask a follow up question here please.

I have tried implementing the above suggestion, using a GNURadio flowgraph to connect two UEs. I am running a 5G SA gNB using the srsRAN_Project. I can connect a single UE to the gNB, using ZeroMQ. It connects, my UE gets an IP address and I can ping the UE from the UPF and vice versa so my basic setyup is working.

I have configured a second UE, setup a second namespace, allocated a second IMSI etc.

When I start the flowgraph, the UEs attach and I get RRC connected. However neither gets an IP address - I don't see "PDU Session Establishment successful". The issue seems to be that each UE gets the same ra-rnti and c-rnti number as below :

UE1
Random Access Transmission: prach_occasion=0, preamble_index=0, ra-rnti=0xf, tti=171
Random Access Complete. c-rnti=0x4601, ta=32
RRC Connected

UE2
Random Access Transmission: prach_occasion=0, preamble_index=0, ra-rnti=0xf, tti=171
Random Access Complete. c-rnti=0x4601, ta=32
RRC Connected

I think this is because each UE is connecting at the same time to the gNB. If I add a delay block into one of the UE paths in the flowgraph, I can get one UE to successfully get an IP address, although both UEs still get the same ra-rnti and c-rnti numbers.

UE1
Attaching UE...
Random Access Transmission: prach_occasion=0, preamble_index=0, ra-rnti=0x39, tti=334
Random Access Complete. c-rnti=0x4601, ta=0
RRC Connected

UE2
Attaching UE...
Random Access Transmission: prach_occasion=0, preamble_index=0, ra-rnti=0x39, tti=334
Random Access Complete. c-rnti=0x4601, ta=0
RRC Connected
PDU Session Establishment successful. IP: 10.45.0.3
RRC NR reconfiguration successful.

Is there something else I need to configure? My understanding was that if two UEs try to connect to the gNB at the same time, they should each implement a random back off and try again.

Thanks

[jonniebeeb]

I save the srsue binary and name it srsue1 before changing anything. Then I change prach.cc, rebuild and the new srsue binary I call srsue2. You need to run two different binaries to make this work.

[jonniebeeb]

Not sure why you are seeing a tti=334 on both UEs. If the change in prach.cc is successful, it should cause the tti to increase. It's as if the changes you've made aren't being used. I'd say check when you rebuild srsRAN_4G that it is rebuilding the srsue binary.

[wmwwimor]

I check the cmakelist in srsRAN_4G，and I'm sure the prach.cc is included in makefile. Besides ,I check the log printed when I remake the srsRAN_4G ，it also include the file prach.cc.
So I think there is sth wrong when I rebuild the project.
I removed the old binary files ,and followed your guide again, I got the same result as yours. Thanks so much !!!
You are right . After sorting out this problem, maybe more gnbs can be expanded.
Thanks for your help again!!

[jonniebeeb]

I’m puzzled as to why it’s not working for you. I have repeated this on a virtual machine I have in the cloud and it works for me, although I have another issue here in that UE3 failed to establish a PDU session which I can see in the amf logs. But the UE does get a unique c-rnti number. Can you put a printf statement in the prach.cc to check what the hold_off count is doing?

[jonniebeeb]

In prach.cc have you included the conditional statement
If(hold_off > 50)

[pgawlowicz]

Could you share configs that you use for each UE?

You can also have a look at this tutorial:
https://openaicellular.github.io/oaic/multi_ue_example.html

It uses the srsenb (4G), but it should be possible to connect the new gnb (5G) using the same approach.

[pgawlowicz]

@wmwwimor @jonniebeeb Please check the new section of our gnb+srsUE tutorial that describes how to emulate multiple-UEs:
https://docs.srsran.com/projects/project/en/latest/tutorials/source/srsUE/source/index.html#multi-ue-emulation

Please remember to clone the newest version of the srsRAN-4G repository.