A network monitoring probe for tracking identifiers corresponding to a user device, wherein the network monitoring probe connected with a source base station, a target base station, a source mobility management entity device (MME) and a target MME in wireless communication network, the network monitoring probe comprising:
- a control plane message monitor, configured to monitor the source base station for receipt of a first control plane packet data unit (PDU) comprising at least a first control plane message transmitted from the source base station to the source MME, which comprises at least a first control plane identifier of the source base station, and a first user device identifier of the user device;
- the control plane message monitor, further configured to monitor the source MME for receipt of a second control plane message transmitted from the source MME to the target MME, the second control plane message including at least a second control plane identifier of the source base station, a second user device identifier and a third user device identifier wherein the second and the third user device identifiers uniquely identify the user device in the wireless communication network;
- the control plane message monitor, further configured to determine whether the first control plane message is a handover required message;
- an identifier comparator, configured to compare the first control plane identifier of the source base station to the second control plane identifier of the source base station and compare the first user device identifier to the second user device identifier;
- an identifier output, configured to output to a storage unit within the network monitoring probe or a management device external to the network monitoring probe, the first user device identifier of the first control plane message and the third user device identifier of the second control plane message as identified first user device identifier and identified second user device identifier of the user device, in response to a determination that the first control plane identifier is identical to the second control plane identifier and the first user device identifier is identical to the second user device identifier;
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- the identifier comparator, further configured to determine that the user device with the identified first and the second user device identifiers commences a S1-based handover, in response to the determination that first control plane identifier is identical to the third control plane identifier, the first user device identifier is identical to the second user device identifier, and the first control plane message is the handover required message;
- the first control plane identifier is a cell global identifier (CGI) of the source base station;
- the second control plane identifier is a CGI of a base station;
- the first control plane message further comprises a third control plane identifier which is a CGI of the target base station to which the user device is to be handed over;
- the first user device identifier is a radio network temporary identifier (RNTI) of the user device;
- the second user device identifier is a RNTI of a user device;
- the first control plane PDU is a S1 Application Protocol PDU;
- the first control plane message is a handover request message transmitted from the source base station to the source MME;
- the second control plane message is a forward relocation request message transmitted from the source the source MME to the target MME;
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- the third user device identifier is an International Mobile Subscriber Identity (IMSI) of a user device.