Why MME sets RestrictDCNR bit in ENDC?

5G NR
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1

Hi All,

In this scenario:
If the UE indicates support for dual connectivity with NR in the Attach Request / Tracking Area Update Request Message, and the MME decides to restrict the use of dual connectivity with NR for the UE, then the MME set the RestrictDCNR bit to “Use of dual connectivity with NR is restricted” in the EPS network feature support IE of the Attach Accept / Tracking Area Update Accept Message.

Here UE indicates support of ENDC in attach request. Bu here also MME sets RestrictDCNR. Why?

2

Because Core network does not support EN-DC.

3

Yes, so we need to be careful from UE and MME end as well.
I find from HSS end as well, there is IE Handover Restriction list which can barred ENDC usage.

4

Yes, this is Absolutely correct statement, this is as per the spec.
Suppose some eNB may be advertising Upper layer indication as true but may not be mapped or any neighbour NR cells are not defined for NSA, then MME can send this.

5

Hi,

we are facing something similar:

  1. UE sends to the MME: …1 … = Dual connectivity with NR: Supported
  2. I can see on the Network Signal Guru that it tries to get 5G NSA, but it drops a few seconds later, and the phone will be connected only in LTE, than it will try again to connect to 5G NSA and so on.
  3. I can see the 5G icon on the phone, even though it is only connected to the LTE.

My assomptions are that the 5G coverage is there, the phone sees it, it tries to do DCNR, but something happens. Would you think this is only a problem of SIM card that was not provisioned in the HSS to support 5G NSA?

Thanks!