Steps 408 to 410 may be summarized as follows: The RAN node returns a Bearer Setup Response to the MME, and the MME creates a Create Bearer Response message to the PGW.

In this embodiment, during the resource requesting process, the MME may assign the TI to the UE, enabling the UE to obtain the TI, so that the UE can still perform normal processing after moving to the GERAN/UTRAN.

A4. PDN Connection Request Process Initiated by a UE

In a fourth embodiment, as shown in FIG. 5, a flow chart of requesting the PDN connection by the UE is described.

In step 501, the UE establishes a PDN Connectivity Request, and sends the PDN Connectivity Request to an RAN.

In step 502, the RAN forwards the PDN Connectivity Request established by the UE to an MME.

In step 503, the MME creates a Default Bearer Request and sends the Default Bearer Request to an SGW.

In step 504, the SGW forwards the Default Bearer Request created by the MME to a PGW.

In step 505, the PGW creates a Default Bearer Response to the SGW.

Steps 501 to 505 may be summarized as follows: The UE sends a PDN Connectivity Request message to the MME, the MME initiates a default bearer establishing procedure to the PGW after selecting the PGW and the SGW, and the PGW responds and creates a Default Bearer Response message and sends it to the MME.

In step 506, the SGW forwards the Default Bearer Response created by the PGW to the MME.

In the step, after receiving the created Default Bearer Request message, the MME sends a Bearer Setup Request to an RAN node.