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In Personal Communications Services (PCS) networks, subscribers' current locations are usually maintained using a two-level hierarchical strategy with two types of databases, specifically, VLRs and HLRs. Location records might be lost due to the malfunction of mobility databases. GSM uses aggressive restoration to restore the HLR data from the VLRs. However, previous work on aggressive restoration is based on periodic checkpointing and might not be feasible in general. This paper proposes a novel aggressive approach, based on aperiodic checkpointing, to back up HLRs and VLRs. The aperiodic checkpointing scheme could use the number of uncheckpointed location records as the threshold value to trigger a backup process. Performance analysis shows that aperiodic checkpointing is more feasible than periodic checkpointing for aggressive restoration.

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