UTRAN & GERAN 3G Inter-PLMN Handover

UTRAN & GERAN 3G Inter-PLMN Handover

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The subscriber's home network is France. The visited network where the subscriber is registered in a VLR (Visitor Location Register) is Germany. The signalling connection between HLR (Home Location Register) and VLR is indicated by dotted lines. The calls for the subscriber are controlled by the MSC collocated to the VLR where the subscriber is registered. This MSC (Mobile Services switching Centre) is called "anchor MSC".

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Handover to a different MSC may occur if the cell serving the subscriber after handover is not controlled by the anchor MSC. This MSC is called the "serving MSC". Even after the call has been handed over to a different MSC, the call control function remains in the anchor MSC. The signalling connection and circuit switched connection established between anchor MSC and serving MSC are indicated by a solid line.

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When the French subscriber registered in a German network roams near the border to the Netherlands, inter-PLMN handover may occur. In this case a Dutch network is the target network. After handover, the anchor MSC located in a German network continues to control the call. The German network remains the visited network where the subscriber is registered. The subscriber's location information stored in the HLR remains unchanged. The signalling and circuit switched connections between the anchor MSC and the previously serving MSC in the German network will be released when the User Equipment (UE) is served by a cell within a Dutch network. The Dutch network becomes the serving network. From the Dutch network the subscriber may be handed over to a Belgian network (see Figure 1).

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It is noteworthy. A problem exists for mobile users when commuting across national borders. Whilst manual network selection may be used to ensure that the user can select the HPLMN (Home PLMN)/ EHPLMN (Equivalent Home-PLMN), many users use Automatic Selection mode; and the ME is only permitted to select PLMNs of a higher priority within the same country in automatic mode. This leads to the situation that, having crossed back into its home country and within HPLMN coverage, an ME might remain camped on the VPLMN in the adjacent territory.

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As a consequence, the user will be charged international roaming rates for all calls made or received until such time as an MS either:

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(a) moves out of VPLMN coverage or

(b) manually selects the HPLMN.

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Note: Power cycling the ME does not solve the problem because the mobile will look for the RPLMN (Roaming-PLMN). The reference to ME is infact a reference also to 3G UE (User Equiment).

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These matter can impact when considering Roaming Cell Site Analysis and Call/Billing Records. It is recommend therefore that reviewing the 3GPP Standards aid understanding how UTRAN and GERAN can function under certain UE conditions particularly when dealing with Network Selection Principles.

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Thanks to 3GPP for provision of information used in this discussion.