RM520N-GL - How to set Follow-On Request (FoR) = 1

IoT Modules 5G Module
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1

Hello Quectel Support,

I’m working with an RM520N module connected to a Free5GC 5G SA core network, and I’ve encountered an issue related to the Follow-On Request (FoR) bit in the NAS Registration Request message.

Problem description

When my UE registers to the 5G core, the FoR bit is always 0 in the 5GS registration type field of the NAS message.

As a result, the AMF sends a UE Context Release Command immediately after completing registration (since FoR=0 implies no more NAS messages are expected).

This causes the N2 connection to be released before I can initiate a PDU Session Establishment Request, so the session setup fails.

Example NAS trace (decoded):

5GS registration type:
Follow-on request bit = 0
Value = 1 (initial registration)

From the AMF log:

Send UE Context Release Command
Release UE Context: N2 Connection Release

What I’ve tried

Attempted to enable “Always-on” via
AT+CGDCONT=1,"IP","internet",,0,0,0,0,,,,,,,,,,,,,,,,1

but this returns ERROR even though the minimal form
AT+CGDCONT=1,"IP","internet"

works fine.

Reference / Expected behavior

From forum discussions and 3GPP behavior:

If FoR=0, AMF will release N2.

Solutions: (1) enable IMS function in the core, or (2) disable IMS APN in the modem.

I would like to know how to configure the RM520N so that it sets FoR=1 during registration or at least keeps the N2 context active after registration to allow immediate PDU Session Establishment.

Questions

  1. Is there an AT command or QCFG parameter that controls the FoR bit or the “Always-on” / persistent PDU session behavior?
  2. Does enabling or disabling IMS via AT+QCFG=“ims”,1 / 0 affect FoR?
  3. Is there any firmware version that exposes a direct control for this behavior?

Environment

  • Module: RM520N-GL
  • Firmware: RM520NGLAAR03A04M4G
  • Network: Free5GC (SA mode, Amarisoft gNB)
  • APNs:
    • CID1: internet
    • CID2: ims (I ve removed this)
    • CID3: sos (I ve removed this)

Any guidance on how to ensure the modem keeps FoR=1 or maintains the N2 signalling connection for PDU session establishment would be very helpful.

Thank you!

2

Dear @stratis_miritzis
Actually, we don’t have AT command to FoR.
It should configure this via base station.
I will send firmware to your email, please check later.