Method and apparatus for avoiding denial of services in mobile communications

1. 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.

2. The method of claim 1 , wherein at least one of the first reject cause and the second reject cause indicates that a general packet radio service (GPRS) is not allowed.

3. The method of claim 1 , wherein at least one of the first reject cause and the second reject cause indicates that an international mobile subscriber identity (IMSI) is unknown in a home location register (HLR).

4. The method of claim 1 , wherein one of the first reject cause and the second reject cause is a reject cause number 7 as defined in a 3 rd Generation Partnership Project (3GPP) specification, and wherein the other one of the first reject cause and the second reject cause is a reject cause number 2 as defined in the 3GPP specification.

5. The method of claim 1 , wherein the network apparatus supports both CS domain services and PS domain services.

6. The method of claim 1 , wherein at least one of the first reject message and the second reject message also comprises a location area update reject message.

7. The method of claim 1 , further comprising:

recording, by the processor, that the first reject cause is received from the first location area.

8. The method of claim 1 , wherein the first reject cause comprises a reject cause in the PS domain, wherein the second reject cause comprises a reject cause in the CS domain, and wherein the storing of the identification of the first location area in the forbidden location area list comprises storing the identification of the first location area in the forbidden location area list upon receiving the reject cause in the PS domain and the reject cause in the CS domain.

9. A method, comprising:

receiving, by a processor of an apparatus, system information broadcasted by a network apparatus in a first location area;

receiving, by the processor, a reject message from the network apparatus;

determining, by the processor and based on the system information, that the network apparatus supports solely single domain services in either a circuit switch (CS) domain or a packet switch (PS) domain; and

in response to receiving the reject message and determining that the network apparatus supports solely the single domain services and that an access to either the CS or the PS domain is denied:

storing, by the processor, an identification of the first location area in a list of forbidden location areas for roaming;

ignoring, by the processor, the network apparatus in the first location area; and

searching, by the processor, for a cell from 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.

10. The method of claim 9 , wherein the reject message comprises a respective reject cause.

11. The method of claim 10 , wherein the reject cause indicates that a general packet radio service (GPRS) is not allowed.

12. The method of claim 10 , wherein the reject cause indicates that an international mobile subscriber identity (IMSI) is unknown in a home location register (HLR).

13. The method of claim 10 , wherein the reject cause is a reject cause number 7 as defined in a 3 rd Generation Partnership Project (3GPP) specification or a reject cause number 2 as defined in the 3GPP specification.

14. The method of claim 9 , wherein the network apparatus supports solely CS domain services or PS domain services.