UE support single or dual registration support in 5G SA

5G NR
1

Hi Experts,
i could not find any IE inside UE capability or Registration or Attach request indicating the support of “single or dual registration”.
Could you please tell me how to understand that?
Thanks!

2

Check for dcnr bit in “UE Network Capability” in Attach Request.

3

dcnr is about ENDC capability (NSA) while UE is accessing to 4G.
Here is the topic about 5G SA

Unfortunately under 23.502 dual registration is mentioned under mobility section only but what I am looking for the procedure of devices working in dual registration mode.

4

Dual registration in N1 mode/SA?

What are the use cases of this scenario?

5

One is, If there is no N26 interface AMF and MME.

6

That’s in S1 mode.

What I asked for is any use case of dual registration in SA.

In NSA, ENDC is a use case.

7

Use case: UE is SA preferred mode and sends both registration request / attach req in one message to AMF, so UE is at both n1 / s1 mode.

I am asking the procedure for this use case.

UE normally should send dual registration if n26 isnt configured…

8

Sorry but there is no use case in SA in my understanding, where equipment is registered in Core networks simultaneously using eutran and nr-ran at the same time.

9

There is use case.

I am asking the procedure for dual registration devices in terms of authentication, how Core network handles that?

Should AMF send identity request to UE upon receiving registration requests?

10

It depends on use case to make practical reasoning. As per documentation available online, UE manages these dual registrations using separate Radio Resource Control (RRC) connections. So registering in EPC through 5G nr-ran or vice virca is out of debate. Its done independently as if a UE is in lte or its in 5G. (Standard Initial Registration).
Further thoughts:

  • Considering N1 mode without N26 interface, such devices must be able to have at least 2 modems to communicate separately and simultaneously in 5G and Lte.
  • Such devices are able to transit the independently running sessions in coverage gaps as required if the networks indicate the support for dual registrations. So such devices play driving role. Each LTE or 5G network doesn’t know by some IE that the device is dual registration mode supporting.
  • Such transitions without N26 interface are conducted through common subscriber information databases, which is udm/hss.
  • Further details on interworking can be learnt here: inside TS 23.502: 5GS to EPS Mobility
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