Method and wireless device for transmitting RRC message when using CP CIOT EPS optimization

A wireless device configured to transmit a non-access stratum (NAS) signaling request message, the wireless device comprising:

• a transceiver;
• at least one processor;
• and
• at least one computer memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:
• transferring, by an NAS layer of the wireless device, an NAS signaling request message to an access stratum (AS) layer of the wireless device to transmit the NAS signaling request message to a network node, wherein the NAS signaling request message includes an indication indicating at least one preferred or required optimization method among (i) optimizing an evolved packet system (EPS) using a control plane (CP) and (ii) optimizing the EPS using a user plane (UP) for a cellular Internet of things (CIoT);
• receiving, by the NAS layer of the wireless device from the AS layer, an NAS signaling accept message or an NAS signaling reject message from the network node, wherein based on the at least one preferred or required optimization method not being supported by the network node, the NAS signaling accept message or the NAS signaling reject message further includes a cause field, wherein based on receiving the NAS signaling reject message, the cause field indicates that the optimization method required by the CIoT device is not supported by a network;
• after the NAS signaling reject message is received, reattempting, by the NAS layer of the wireless device, to transfer the NAS signaling request message to the AS layer until a threshold number of re-attempts is reached;
• and
• performing, by the NAS layer of the wireless device, to select a public land mobile network (PLMN) that supports the optimization method required by the CIoT device.

A processing apparatus configured to control a wireless device to transmit a non-access stratum (NAS) signaling request message, the processing apparatus comprising:

• at least one processor;
• and
• at least one computer memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:
• transferring, by an NAS layer of the wireless device, an NAS signaling request message to an access stratum (AS) layer of the wireless device to transmit the NAS signaling request message to a network node, wherein the NAS signaling request message includes an indication indicating at least one preferred or required optimization method among (i) optimizing an evolved packet system (EPS) using a control plane (CP) and (ii) optimizing the EPS using a user plane (UP) for a cellular Internet of things (CIoT);
• receiving, by the NAS layer of the wireless device from the AS layer, an NAS signaling accept message or an NAS signaling reject message from the network node, wherein based on the at least one preferred or required optimization method not being supported by the network node, the NAS signaling accept message or the NAS signaling reject message further includes a cause field, wherein based on receiving the NAS signaling reject message, the cause field indicates that the optimization method required by the CIoT device is not supported by a network;
• after the NAS signaling reject message is received, reattempting, by the NAS layer of the wireless device, to transfer the NAS signaling request message to the AS layer until a threshold number of re-attempts is reached;
• and
• performing, by the NAS layer of the wireless device, to select a public land mobile network (PLMN) that supports the optimization method required by the CIoT device.