Apple patents 5G-to-4G handoff method for stable data connections

1. An apparatus, comprising: a processor configured to cause a wireless device to: establish a fifth generation new radio (5G NR) cellular link that provides access to a fifth generation core (5GC) network; establish a protocol data unit (PDU) session with the 5GC network; and determine that inter-radio access technology (inter-RAT) mobility from the 5G NR cellular link to a long term evolution (LTE) cellular link is triggered; determine one or more quality of service (QoS) flow descriptions for the PDU session; determine whether to handover the PDU session to the LTE cellular link or re-establish the PDU session via the LTE cellular link based at least in part on the one or more QoS flow descriptions for the PDU session; determine that one or more QoS flow descriptions of the PDU session are not supported by the LTE cellular link; provide a PDU session modification request based at least in part on determining that inter-RAT mobility from the 5G NR cellular link to a LTE cellular link is triggered and determining that one or more QoS flow descriptions of the PDU session are not supported by the LTE cellular link, wherein the PDU session modification request comprises a request to modify the QoS flow descriptions of the PDU session; when a PDU session modification command message is received in response to the PDU session modification request and when the PDU session modification command message indicates to modify the QoS flow descriptions of the PDU session as requested, the process or is further configured to cause the wireless device to: perform PDU session handover when performing inter-RAT mobility from the 5G NR cellular link to a LTE cellular link based at least in part on the PDU session modification command message indicating to modify the QoS flow descriptions of the PDU session as requested; and when a PDU session modification reject message is received in response to the PDU session modification request, the processor is further configured to cause the wireless device to: re-establish the PDU session via the LTE link when performing inter-RAT mobility from the 5G NR cellular link to a LTE cellular link based at least in part on the PDU session modification reject message.