Error handling on missing configuration for inter-system change in mobile communications

1. A method, comprising:

performing, by a processor of an apparatus implemented in a user equipment (UE), a protocol data unit (PDU)-related procedure with a wireless network;

detecting, by the processor while the UE is in a 5th Generation System session management (5GSM) procedure, whether there is an error in the PDU-related procedure; and

handling, by the processor, the error before switching to an Evolved Packet System (EPS) from a 5th Generation System (5GS) responsive to detecting the error in the PDU-related procedure,

wherein the PDU-related procedure comprises a PDU session modification procedure,

wherein the detecting whether there is an error in the PDU-related procedure comprises:

checking whether an operation code indicates creating a new EPS bearer or modifying an existing EPS bearer; and

detecting an error in an EPS Session Management (ESM) parameter by:

checking whether a mapped EPS bearer context includes an invalid or missing mapped EPS quality of service (QoS) parameter or an invalid or missing traffic flow template; or

checking whether the mapped EPS bearer context includes an invalid mapped extended EPS QoS parameter, an invalid access point name aggregate maximum bit rate (APN-AMBR) or an invalid extended APN-AMBR, and

wherein the handling of the error comprises:

transmitting a PDU SESSION MODIFICATION COMPLETE message to the wireless network for an ongoing PDU session modification procedure; and

initiating a new PDU session modification procedure by transmitting a PDU SESSION MODIFICATION REQUEST message to the wireless network to delete the mapped EPS bearer context with a 5GSM cause number.

2. The method of claim 1 , wherein the detecting whether there is an error in the PDU-related procedure further comprises:

receiving a 5GSM message from the wireless network, the 5GSM message comprising parameters for an inter-system change; and

determining whether at least one of the parameters is invalid or missing.

3. An apparatus implemented in a user equipment (UE), comprising:

a transceiver configured to wirelessly communicate with a wireless network; and

a processor coupled to the transceiver, the processor configured to perform operations comprising:

performing, via the transceiver, a protocol data unit (PDU)-related procedure with a wireless network;

detecting, via the transceiver and while the UE is in a 5th Generation System session management (5GSM) procedure, whether there is an error in the PDU-related procedure; and

handling, via the transceiver, the error before switching to an Evolved Packet System (EPS) from a 5th Generation System (5GS) responsive to detecting the error in the PDU-related procedure,

wherein the PDU-related procedure comprises a PDU session establishment procedure,

wherein the detecting whether there is an error in the PDU-related procedure comprises:

checking whether an operation code indicates creating a new EPS bearer or modifying an existing EPS bearer; and

detecting an error in an EPS Session Management (ESM) parameter by:

checking whether a mapped EPS bearer context includes an invalid or missing mapped EPS quality of service (QoS) parameter or an invalid or missing traffic flow template; or

checking whether the mapped EPS bearer context includes an invalid mapped extended EPS QoS parameter, an invalid access point name aggregate maximum bit rate (APN-AMBR) or an invalid extended APN-AMBR, and

wherein the handling of the error comprises initiating a new PDU session modification procedure by transmitting a PDU SESSION MODIFICATION REQUEST message to the wireless network to delete the mapped EPS bearer context with a 5GSM cause number.

4. The method of claim 3 , wherein the detecting whether there is an error in the PDU-related procedure further comprises:

receiving a 5GSM message from the wireless network, the 5GSM message comprising parameters for an inter-system change; and

determining whether at least one of the parameters is invalid or missing.