UE fails to attach: srsUE + srsRAN gNB + Open5GS 5G Core (ZMQ)

[AMINEF1]

I am trying to run srsRAN Project gNB together with Open5GS (5G Core) using ZMQ-based virtual RF, and connect an srsUE (from srsRAN_4G) as the UE.
The gNB starts correctly, derives SSB parameters, and successfully connects to the AMF (N2: Connection to AMF completed). ZMQ ports (2000/2001) are open and traffic is visible, and both gNB and UE PHY layers initialize without errors.

However, the UE remains stuck at Attaching UE... and never transitions to RRC_CONNECTED. No PRACH attempt, no Found SSB, and no RRC or NAS signaling appears on the gNB or Open5GS side. The tun_srsue interface is never created.

I am using FDD Band 3 (n3) with prach_config_index = 1, matching PLMN/TAC/APN/IMSI across gNB, UE, and Open5GS. I have verified ZMQ port direction, sample rates, bandwidth (20 MHz), and namespace setup. Logs show no explicit errors—only inactivity after PHY initialization.

The UE gets stuck and keeps waiting to connect ("Attaching UE...") and never completes the attachment procedure.
The gNB connects to the AMF successfully, but the UE does not proceed beyond the initial attach step

Could you please help me understand why the UE is not completing the connection?

[s5uishida]

@AMINEF1

There may not be enough CPU cores.
If you are using a virtual machine, try setting the number of CPU cores to 5.

Below are my notes.

https://github.com/s5uishida/build_srsran_5g_zmq

FYI.