UE behavior when VoNR unsupported, network attempts dedicated bearer

5G NR
1

UE supports VoLTE and SA, but not VoNR. UE capability Info to the n/w clearly indicates that the device does not support VoNR. When a call is triggered in 5G SA, and if the network configures the VoNR bearer (ignoring UE capability) what should the UE do here? Any specification reference would be helpful

2
  • The UE should reject the VoNR bearer establishment attempt with an appropriate cause code.
  • According to 3GPP TS 24.501 (5G NAS protocol), section 6.4.1.3 “UE requested PDU session establishment procedure accepted by the network,” when the network attempts to establish a PDU session with parameters the UE cannot support, the UE should:
  • Send a PDU SESSION ESTABLISHMENT REJECT message
  • Include cause #43 “Invalid PDU session identity” or the appropriate failure cause
  • Additionally, 3GPP TS 38.331 (5G RRC protocol) specifies that when receiving RRC configuration for capabilities the UE doesn’t support, the UE should:
  • Reject the configuration
  • Send an RRC reconfiguration failure message
  • For fallback procedures, 3GPP TS 23.502 section 4.13 details the “EPS Fallback for IMS voice” procedure. The UE should trigger EPS fallback to utilize its VoLTE capability instead.