Short message transmission and handover procedures

1. A connectivity-related network entity comprising:

a receiver, which, in operation, receives, from a Packet Data Network (PDN) gateway and a Serving Gateway (SGW), a Short Message Service (SMS) message to be sent in a downlink;

circuitry, which is coupled to the receiver and which, in operation,

determines to use a control plane only, out of the control plane and a user plane, to transfer the SMS message, and

encapsulates the SMS message in a security protected Non-Access Stratum (NAS) message; and

a transmitter, which is couple to the circuitry and which, in operation, transmits a trigger message to a user equipment to initiate establishment of connectivity with the user equipment via the control plane only and not via the user plane, wherein the user equipment starts a timer when the establishment of the control plane connectivity is initiated;

wherein,

the receiver, in operation, receives a response message from the user equipment; and

the transmitter, in operation, transmits the security protected NAS message to the user equipment, in receipt of which the user equipment stops the timer.

2. The connectivity-related network entity according to claim 1 , wherein the timer is stopped in response to one or both of:

a) establishment of a bearer for the user plane; and

b) release of a Radio Resource Control (RRC) connection.

3. The connectivity-related network entity according to claim 1 , wherein the response message from the user equipment to the connectivity-related network entity is a Non-Access Stratum (NAS) service request to establish the connectivity.

4. The connectivity-related network entity according to claim 1 , which is a Mobility Management Entity (MME).

5. The connectivity-related network entity according to claim 1 , wherein the timer is a control-plane establishment timer or a radio resource release timer.

6. The connectivity-related network entity according to claim 1 , wherein the timer is T3417 timer defined in 3rd Generation Partnership Project (3GPP) standards.

7. The connectivity-related network entity according to claim 1 , wherein the transmitted security protected NAS message is transferred by a base station, via a Radio Resource Control (RRC) interface, to the user equipment.

8. A method performed by a connectivity-related network entity, the method comprising:

receiving, from a Packet Data Network (PDN) gateway and a Serving Gateway (SGW), a Short Message Service (SMS) message to be sent in a downlink;

determining to use a control plane only, out of the control plane and a user plane, for transferring the SMS message;

transmitting a trigger message to a user equipment to initiate establishment of connectivity with the user equipment via the control plane only and not via the user plane, wherein the user equipment starts a timer when the establishment of the control plane connectivity is initiated;

receiving a response message from the user equipment;

encapsulating the SMS message in a security protected Non-Access Stratum (NAS) message; and

transmitting the security protected NAS message to the user equipment, in receipt of which the user equipment stops the timer.

9. The method according to claim 8 , wherein the user equipment stops the timer in response to one or both of:

a) establishment of a bearer for the user plane; and

b) release of a Radio Resource Control (RRC) connection.

10. The method of claim 8 , wherein the response message from the user equipment to the connectivity-related network entity is a Non-Access Stratum (NAS) service request to establish the connectivity.

11. The method of claim 8 , wherein the connectivity-related network entity is a Mobility Management Entity (MME).

12. The method of claim 8 , wherein the timer is a control-plane establishment timer or a radio resource release timer.

13. The method of claim 8 , wherein the timer is T3417 timer defined in 3rd Generation Partnership Project (3GPP) standards.

14. The method of claim 8 , wherein

the transmitted security protected NAS message is transferred by a base station, via a Radio Resource Control (RRC) interface, to the user equipment.