Method for subscriber identity determination, network elements and wireless communication system thereof
A method and network elements for obtaining a subscriber identity of a User Equipment ( 105 ) being served by a LTE cell ( 104 ) exploits a conventional handover procedure by generating a “fake” handover request at the LTE (source) cell ( 104 ) designating a 3G cell ( 102 ) as the target. The target 3G cell is arranged to forward the subscriber identity which is included in a relocation request message received from a core network ( 107 ) to the LTE cell and to send a relocation failure message back to the core network.
1. A method for determining a subscriber identity of a wireless communication unit located in a first cell of a wireless communication system comprising a plurality of network elements and a core network, the method comprising, at a first network element:
serving the first cell,
obtaining an identity of a second network element,
initiating a handover procedure by generating a handover required message that designates the second network element as a handover target cell and that includes information to identify the first cell, and
sending the handover required message to the core network,
and the method comprising, at the second network element:
receiving, from the core network, a relocation request message requesting handover of the wireless communication unit from the first cell to the second network element that includes information to identify the first cell and the subscriber identity of the wireless communication unit,
sending to the first network element a message including the received subscriber identity, and
sending to the core network, a relocation failure message.
2. The method of claim 1 , wherein obtaining an identity of the second network element comprises provisioning the first network element with the identity of the second network element.
3. The method of claim 1 , wherein obtaining an identity of the second network element comprises, at the second network element, sending a message to the first network element containing the identity of the second network element.
4. The method of claim 1 , wherein the handover required message comprises an S1 Handover Required message comprising a Source to Target Transparent Container that includes the identity of the first cell in a last visited cell list of User Equipment History Information.
5. The method of claim 1 , wherein a cause code included in the handover required message is one that will not result in an attempt by the core network to modify the behaviour of a handover process.
6. The method of claim 1 , including, at the first network element sending an alert message to the second network element indicating that a fake handover is being attempted.
7. The method of claim 6 , wherein said alert message comprises a copy of the handover required message.
8. The method of claim 6 , wherein said alert message includes an identifier that facilitates identification of the handover required message.
9. The method of claim 1 , wherein the subscriber identity included in the relocation request message received at the second network element and included in the message sent by the second network element to the first network element comprises a Permanent Non-Access Stratum, NAS, User Equipment identity.
10. A first network element for determining a subscriber identity of a wireless communication unit located in a first cell of a wireless communication system comprising a plurality of network elements and a core network, the first network element serving a first cell comprising:
a first memory configured to store an identity of a second network element, and
a first signal processor configured to:
generate a handover required message for transmission to the core network, wherein the handover required message designates the second network element as a handover target and includes information to identify the first cell, and
receive a subscriber identity message from the second network element containing the subscriber identity of the wireless communication unit that was generated in response to the subscriber identity message and a subscriber identity received at the second network element.
11. The first network element of claim 10 , wherein the first signal processor is arranged to include a cause code in the handover required message that helps to identify the handover required message as being a fake handover attempt.
12. The first network element of claim 10 , wherein the first signal processor is arranged to generate an alert message for transmitting to the second network element which indicates that a fake handover is being attempted.
13. A second network element for determining a subscriber identity of a wireless communication unit located in a first cell of a wireless communication system comprising a plurality of network elements and a core network, the second network element comprising:
a receiver configured to receive a relocation request message, which includes information to identify a first cell served by a first network element and a subscriber identity of a wireless communication unit, from the core network,
a transmitter configured to transmit a subscriber identity message to the first network element containing the subscriber identity of a wireless communication unit, and
a second signal processor configured to:
generate a subscriber identity message for transmission to the first network element in response to receiving the relocation request message, and
generate a relocation failure message for transmission to the core network.
14. The second network element of claim 13 , wherein the transmitter is further configured to transmit a message containing the identity of the second network element to the first network element.
15. A wireless communication system comprising:
a core network,
at least one wireless communication unit,
a second network element, and
a first network element serving a first cell comprising:
a first memory configured to store an identity of the second network element, and
a first signal processor configured to:
generate a handover required message for transmission to the core network wherein the handover required message designates the second network element as a handover target and includes information to identify the first cell, and
receive a subscriber identity message from the second network element containing the subscriber identity of the wireless communication unit, and
wherein the second network element comprises:
a second signal processor configured to:
generate a subscriber identity message for transmission to the first network element on receiving a relocation request message including information to identify the first cell and the subscriber identity, from the core network, and
generate a relocation failure message for transmission to the core network.
16. The wireless communication system of claim 15 , wherein the first cell is a Long Term Evolution, LTE, cell.