Method for performing a tracking area update procedure when MINT service is supported, and user equipment therefor

A user equipment (UE), the UE comprising:

• at least one processor;
• and
• at least one computer memory operably connectable to the at least one processor and storing instructions that, when executed by the at least one processor, perform operations comprising:
• if the UE supports a minimization of service interruption (MINT)-evolved packet system (EPS), setting a MINT-EPS bit to “MINT-EPS supported” in capability information;
• upon selecting a public land mobile network (PLMN) for disaster roaming in an EPS, performing a tracking area update procedure with an EPS update type set to “disaster roaming update”;
• transmitting the capability information during the tracking area update procedure;
• receiving a response message,
• wherein if the response message is a tracking area update accept message, the tracking area update accept message includes at least one a disaster roaming wait range and a disaster return wait range, and
• wherein if the response message is a tracking area update reject message, the tracking area update reject message includes a cause value to “roaming not allowed in this tracking area” and includes the disaster return wait range;
• generating a first random number within the disaster roaming wait range;
• starting a first timer based on the generated first random number;
• generating a second random number with the disaster return wait range;
• starting a second timer with the generated second random number value;
• and
• upon expiry of the second timer based on the disaster return wait range, not starting the second timer with the disaster return wait range again until the UE selects any PLMN for a disaster roaming service,
• wherein upon determining that a disaster condition has ended, the UE stops the first timer based on the disaster roaming wait range and performs a PLMN selection, except if the UE already selected an allowable PLMN.

A semiconductor chipset, comprising:

• at least one processor;
• and
• at least one memory capable of storing instructions and being connected electrically to the at least one processor operably,
• wherein operations, performed when the instructions are executed by the at least one processor, includes:
• if an UE supports a minimization of service interruption (MINT)-evolved packet system (EPS), setting a MINT-EPS bit to “MINT-EPS supported” in capability information;
• upon selecting a public land mobile network (PLMN) for disaster roaming in an EPS, performing a tracking area update procedure with an EPS update type set to “disaster roaming update”;
• transmitting the capability information during the tracking area update procedure;
• receiving a response message,
• wherein if the response message is a tracking area update accept message, the tracking area update accept message includes at least one a disaster roaming wait range and a disaster return wait range, and
• wherein if the response message is a tracking area update reject message, the tracking area update reject message includes a cause value to “roaming not allowed in this tracking area” and includes the disaster return wait range;
• generating a first random number within the disaster roaming wait range;
• starting a first timer based on the generated first random number;
• generating a second random number with the disaster return wait range;
• starting a second timer with the generated second random number value;
• and
• upon expiry of the second timer based on the disaster return wait range, not starting the second timer with the disaster return wait range again until the UE selects any PLMN for a disaster roaming service,
• wherein upon determining that a disaster condition has ended, the UE stops the first timer based on the disaster roaming wait range and performs a PLMN selection, except if the UE already selected an allowable PLMN.