UE attach failure on ORAN experimental profile — srsRAN 4G UE + srsRAN Project gNB + ZMQ
Yoon Jae Hwang
I'm running an experiment on the ORAN experimental profile and
cannot get a srsRAN 4G UE to attach to a srsRAN Project gNB over ZMQ. The 5G core and
RIC come up cleanly, but the UE never reaches "Network attach successful".
--- Stack (startup order followed exactly) ---
Component | Version / Source
-------------------|------------------------------------------------------------------
5G Core | Open5GS via Docker (srsRAN_Project/docker/docker-compose.yml)
Near-RT RIC| FlexRIC br-flexric branch, built with GCC-12 / SWIG 4.2.1
gNB | srsRAN Project (latest main), ZMQ mode, Band 3, 20 MHz, dl_arfcn=369460
UE | srsRAN 4G (srsue), ZMQ mode, NR SA, Band 3
--- gNB config key parameters ---
dl_arfcn: 369460
band: 3
channel_bandwidth_MHz: 20
common_scs: 15
coreset0_index: 6
ss0_index: 0
prach_config_index: 1
AMF addr: 10.53.1.2:38412 (Open5GS Docker bridge)
E2 RIC addr: 127.0.0.1:36421
--- UE config key parameters ---
ssb_arfcn: 367450
bands: 3 (NR SA, nof_carriers=1)
srate: 23.04e6
ZMQ: tx -> tcp://127.0.0.1:2001, rx <- tcp://127.0.0.1:2000
IMSI: 001010123456780
K/OPC: matching Open5GS default subscriber
--- What I observe ---
- Open5GS AMF comes up and gNB connects:
"N2: Connection to AMF on 10.53.1.2:38412 completed"
- FlexRIC nearRT-RIC connects to gNB:
"E2AP: Connection to Near-RT-RIC on 127.0.0.1:36421 completed"
- srsue starts and attempts attach but not attaching, the terminal indicates
"UE Attaching..." But not progressing
--- What I have already tried ---
- coreset0_index: 6 (docs indicate 12 causes PDCCH incompatibility with srsUE)
- srate = 23.04e6 set in both gNB and UE configs (required for NR SA)
- Port 9999 remapped to 19999 to avoid conflict with nginx/K8s OSC stack
- Subscriber pre-provisioned in Open5GS (IMSI, K, OPC match)
--- Questions ---
1. Is there a known incompatibility between srsRAN Project gNB and srsRAN 4G UE
in the current ORAN profile environment (kernel version, UHD version, etc.)?
2. Does the ORAN profile's pre-installed OSC RIC stack interfere with ports or
networking in a way that affects ZMQ transport or NGAP connectivity?
3. Are there profile-specific gNB or UE config constraints (e.g., required ARFCN,
PRACH index, PLMN, TAC) that differ from the srsRAN defaults?
Any guidance would be appreciated.
Thank you,
Yoonjae Hwang
David M Johnson
I ran a quick test of the O-RAN profile this morning, and its
installation of srsRAN_Project gnb, srsRAN 4G UE, and Open5GS, and
associated instructions work fine and allow the UE to attach over ZMQ.
If you're following the profile instructions and using the profile's
config to get your srsue connected to the gnb, please point me to your
experiment so I can attempt to reproduce, thanks!
That said, I can't quite tell from your message if you manually
installed all the pieces you mention below; although certainly the
dockerized open5gs and flexric you installed manually, since the profile
does not automatically install them. In any case, if you manually
installed and configured srsRAN or open5gs, there could be a number of
conflicts (config files, ports already in use, connections to the
"other" 5G core), so could be tricky to debug.
You can disable some of what the profile automatically installs to avoid
conflicts with your custom configuration: deselect
* Install O-RAN SC RIC
* Install Open5GS
* Build srsRAN_Project
* Build srsRAN_4G
(although you might consider using the profile's install/config of
srsRAN_Project and srsRAN_4G, since those are well-tested in the
installed config.)
David
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Yoon Jae Hwang
Hi,
Thank you for the previous guidance. We followed your advice and created a fresh experiment with the following profile options deselected: Install O-RAN SC RIC, Install Open5GS, Build srsRAN_Project, Build srsRAN_4G. We then manually built all components from source.
The gNB connects to both the Open5GS AMF and FlexRIC RIC successfully. The ZMQ TCP connections between gNB and UE are established (ESTAB on ports 2000 and 2001). However, the UE is still stuck at "Attaching UE..." and the gNB log shows the following:
[zmq:tx:0:0] [I] Waiting for data.
[zmq:rx:0:0] [I] Waiting for reading samples. Completed 0 of 23040 samples.
After reading the srsRAN_Project ZMQ source, we believe the root cause is a timing deadlock:
- The gNB ZMQ RX is receiving 0-byte UL responses from srsRAN_4G UE (before cell sync, the UE TX sends empty packets)
- This stalls the gNB's internal timing loop, preventing it from generating DL samples
- Without DL, the UE cannot sync → deadlock
We have tried:
- srsRAN_4G built from latest master (commit 6bcbd9e5b)
- srsRAN_4G built from release_23_11
Both exhibit the same behavior. Our gNB config uses Band 3, 20 MHz, ZMQ, dl_arfcn=369460, coreset0_index=6.
Questions:
1. What exact version/commit of srsRAN_4G and srsRAN_Project does the ORAN profile install?
2. Is there a specific gNB ZMQ config that differs from the standard setup for use with srsUE?
3. Is there a known workaround for the ZMQ UL-stalls-DL issue between these two codebases?
Thank you,
Yoonjae Hwang
Dustin Maas
Repeating the same message will not result in faster answers ;)
On 7 May 2026, at 15:53, Yoon Jae Hwang wrote:
Hi,
Thank you for the previous guidance. We followed your advice and created a fresh experiment with the following profile options deselected: Install O-RAN SC RIC, Install Open5GS, Build srsRAN_Project, Build srsRAN_4G. We then manually built all components from source.
The gNB connects to both the Open5GS AMF and FlexRIC RIC successfully. The ZMQ TCP connections between gNB and UE are established (ESTAB on ports 2000 and 2001). However, the UE is still stuck at "Attaching UE..." and the gNB log shows the following:
[zmq:tx:0:0] [I] Waiting for data.
[zmq:rx:0:0] [I] Waiting for reading samples. Completed 0 of 23040 samples.
After reading the srsRAN_Project ZMQ source, we believe the root cause is a timing deadlock:
- The gNB ZMQ RX is receiving 0-byte UL responses from srsRAN_4G UE (before cell sync, the UE TX sends empty packets)
- This stalls the gNB's internal timing loop, preventing it from generating DL samples
- Without DL, the UE cannot sync → deadlock
We have tried:
- srsRAN_4G built from latest master (commit 6bcbd9e5b)
- srsRAN_4G built from release_23_11
Both exhibit the same behavior. Our gNB config uses Band 3, 20 MHz, ZMQ, dl_arfcn=369460, coreset0_index=6.
Questions:
1. What exact version/commit of srsRAN_4G and srsRAN_Project does the ORAN profile install?
2. Is there a specific gNB ZMQ config that differs from the standard setup for use with srsUE?
3. Is there a known workaround for the ZMQ UL-stalls-DL issue between these two codebases?
Thank you,
Yoonjae Hwang
On Monday, May 4, 2026 at 6:59:52 AM UTC-7 john...@flux.utah.edu wrote:
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Yoon Jae Hwang
Kirk Webb
think he was just trying to get through.
-Kirk
Dustin Maas
Ah.. apologies for the misunderstanding Yoon!
On 8 May 2026, at 16:46, Kirk Webb wrote:
To be fair, Yoon's messages were held up pending admin review, so I
think he was just trying to get through.-Kirk
On Fri, May 8, 2026 at 4:40 PM Dustin Maas dusti...@gmail.com wrote:
Repeating the same message will not result in faster answers ;)
On 7 May 2026, at 15:53, Yoon Jae Hwang wrote:
Hi,
Thank you for the previous guidance. We followed your advice and created a fresh experiment with the following profile options deselected: Install O-RAN SC RIC, Install Open5GS, Build srsRAN_Project, Build srsRAN_4G. We then manually built all components from source.
The gNB connects to both the Open5GS AMF and FlexRIC RIC successfully. The ZMQ TCP connections between gNB and UE are established (ESTAB on ports 2000 and 2001). However, the UE is still stuck at "Attaching UE..." and the gNB log shows the following:
[zmq:tx:0:0] [I] Waiting for data.
[zmq:rx:0:0] [I] Waiting for reading samples. Completed 0 of 23040 samples.
After reading the srsRAN_Project ZMQ source, we believe the root cause is a timing deadlock:
The gNB ZMQ RX is receiving 0-byte UL responses from srsRAN_4G UE (before cell sync, the UE TX sends empty packets)
This stalls the gNB's internal timing loop, preventing it from generating DL samples
Without DL, the UE cannot sync → deadlock
We have tried:
srsRAN_4G built from latest master (commit 6bcbd9e5b)
srsRAN_4G built from release_23_11
Both exhibit the same behavior. Our gNB config uses Band 3, 20 MHz, ZMQ, dl_arfcn=369460, coreset0_index=6.
Questions:
What exact version/commit of srsRAN_4G and srsRAN_Project does the ORAN profile install?
Is there a specific gNB ZMQ config that differs from the standard setup for use with srsUE?
Is there a known workaround for the ZMQ UL-stalls-DL issue between these two codebases?
Thank you,
Yoonjae Hwang
On Monday, May 4, 2026 at 6:59:52 AM UTC-7 john...@flux.utah.edu wrote:
Hi Yoonjae,
I ran a quick test of the O-RAN profile this morning, and its
installation of srsRAN_Project gnb, srsRAN 4G UE, and Open5GS, and
associated instructions work fine and allow the UE to attach over ZMQ.
If you're following the profile instructions and using the profile's
config to get your srsue connected to the gnb, please point me to your
experiment so I can attempt to reproduce, thanks!That said, I can't quite tell from your message if you manually
installed all the pieces you mention below; although certainly the
dockerized open5gs and flexric you installed manually, since the profile
does not automatically install them. In any case, if you manually
installed and configured srsRAN or open5gs, there could be a number of
conflicts (config files, ports already in use, connections to the
"other" 5G core), so could be tricky to debug.You can disable some of what the profile automatically installs to avoid
conflicts with your custom configuration: deselect
- Install O-RAN SC RIC
- Install Open5GS
- Build srsRAN_Project
- Build srsRAN_4G
(although you might consider using the profile's install/config of
srsRAN_Project and srsRAN_4G, since those are well-tested in the
installed config.)David
On 5/1/26 14:57, Yoon Jae Hwang wrote:
Hi POWDER team,
I'm running an experiment on the ORAN experimental profile and
cannot get a srsRAN 4G UE to attach to a srsRAN Project gNB over ZMQ.
The 5G core and
RIC come up cleanly, but the UE never reaches "Network attach successful".--- Stack (startup order followed exactly) ---
Component Version / Source
- Open5GS AMF comes up and gNB connects:
"N2: Connection to AMF on 10.53.1.2:38412 completed"
- FlexRIC nearRT-RIC connects to gNB:
"E2AP: Connection to Near-RT-RIC on 127.0.0.1:36421 completed"
- srsue starts and attempts attach but not attaching, the terminal indicates
"UE Attaching..." But not progressing
--- What I have already tried ---
- coreset0_index: 6 (docs indicate 12 causes PDCCH incompatibility with
srsUE)
- srate = 23.04e6 set in both gNB and UE configs (required for NR SA)
- Port 9999 remapped to 19999 to avoid conflict with nginx/K8s OSC stack
- Subscriber pre-provisioned in Open5GS (IMSI, K, OPC match)
--- Questions ---
- Is there a known incompatibility between srsRAN Project gNB and
srsRAN 4G UE
in the current ORAN profile environment (kernel version, UHD
version, etc.)?
- Does the ORAN profile's pre-installed OSC RIC stack interfere with
ports or
networking in a way that affects ZMQ transport or NGAP connectivity?
- Are there profile-specific gNB or UE config constraints (e.g.,
To view this discussion visit https://groups.google.com/d/msgid/powder-users/CAFKO4CHD_k45bDEbLkt8xBXfcrHeDwCdxMH-6z8_uS80fWJLEA%40mail.gmail.com.