Method and apparatus for avoiding denial of services in mobile communications

A method, comprising:

• transmitting, by a processor of an apparatus, a first kind of request and a second kind of request to a network apparatus of a network, wherein the first kind of request and the second kind of request are transmitted separately, and wherein the network is a Network Operation Mode II (NMO-II) network;
• receiving, by the processor, a non-integrity protected first reject message with a first reject cause from one of a circuit switch (CS) domain and a packet switch (PS) domain of the network apparatus in a first location area as a result of transmitting the first kind of request to the network apparatus;
• receiving, by the processor, a non-integrity protected second reject message with a second reject cause different than the first reject cause from the other one of the CS domain and the PS domain of the network apparatus in the first location area as a result of transmitting the second kind of request which is different from the first kind of request and separately transmitted to the network apparatus;
• determining, by the processor responsive to receiving the first and the second reject messages, that an access to the PS domain and the CS domain in the first location area is not allowed;
• storing, by the processor, an identification of the first location area in a list of forbidden location areas for roaming responsive to the first and the second reject messages being respectively received from the CS domain and the PS domain of the network apparatus of the first location area;
• and
• searching, by the processor, for a second location area or tracking area different from the first location area,
• wherein the storing of the identification of the first location area comprises:
• maintaining a flag to record whether a reject cause in the PS domain or another reject cause in the CS domain is received;
• setting the flag when one of the PS domain and the CS domain is rejected;
• and
• storing the identification of the first location area responsive to the flag being set and receiving the reject cause from the other one of the CS domain and the PS domain.