5G紧急呼叫流程分析

目前5GNR网络还不支持紧急呼叫走VoNR

再看3GPP R16 TS 24.501，UE在紧急呼叫回落情况下disable N1，目的就是在紧急呼叫过程中不会handover到5G网络。紧急呼叫结束，打开N1 mode，终端快速重选到5G网络。

UE disable N1 for emergency service fallback; and UE re-enable N1 after the emergency service ends.

本文分析两种5G NR下紧急呼叫流程

紧急呼叫EPSFB到LTE

[log]

[ATP_AT_I_0,ch3, s00003f8f]ATDE120

[NW->MS] NR_RRCRelease (NARFCN[633984], PCI[131]) (redirectedCarrierInfo[1], suspendConfig[0])

MSG_ID_NAS_SV_NRRC_RAT_CHANGE_IND     //5G->4G

PLMN:46011f RAT_NR is disabled because of NWSEL_EMC_EPSFB

[MS->NW] EMM_Tracking_Area_Update_Request(EPS update type="EMM_UPDATE_TYPE_TAU", active flag="KAL_TRUE")     // N1 mode:Not sup