Method and apparatus for recovery from fallback for cellular internet of things device

Abstract

There is disclosed a first method for a UE, wherein the UE is in 5GMM-CONNECTED mode with RRC inactive indication. The first method comprises: establishing a PDU session for sending data over the control plane; determining that there is data to be sent in an UL NAS TRANSPORT message; in response to the determining, requesting lower layers to resume an RRC connection; and upon receiving a fallback indication from the lower layers in response to the requesting, entering 5GMM-IDLE mode. Also disclosed is a second method for a UE, wherein the UE is in 5GMM-CONNECTED mode with RRC inactive indication. The second method comprises: establishing a PDU session for sending data over the user plane; determining that there is user data to be sent over the user plane; determining that there is no pending NAS procedure; and upon receiving a fallback indication from the lower layers, in response to the determining, entering 5GMM-IDLE mode. Also disclosed is a third method for a UE, wherein the UE is in 5GMM-CONNECTED mode with RRC inactive indication. The third method comprises: in response to receiving, from lower layer, a suspend indication, determining the type of the suspend indication; and entering a NAS mode according to the determined type of the suspend indication.