الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The lost calls are the major problem that hardly degrades the performance of Personal Communication Service (PCS) of networks. Lost calls arise when the location information of mobile users stored in Home Location Register (HLR) is corrupted or outdated. In order to tackle this situation, it is becoming necessary to tolerate HLR failure by implementing efficient recovery schemes. Traditionally, HLR mobility database is periodically checkpointed and restored after failure by reloading the backup. However, choosing the optimal checkpointing interval is still a challenge, then, backup information may be obsolete. On the other hand, to our best of knowledge, none of mobility database failure restoration techniques take the hardware crashes into consideration. This thesis proposes a reliable HLR failure detection and recovery strategy based on using a double edged mobility database (HLR, and BC). The proposed strategy is a fault tolerant as it examines the availability of both the main HLR of the system as well the backup (BC) continuously, then take the suitable actions to keep the system working with relatively no lost calls. from another point of view, the proposed architecture is double edged as both HLR and BC are employed in the system operation all the time. Experimental results have shown that the proposed failure detection and recovery strategy outperforms traditional checkpointing techniques as it introduces better performance with relatively no lost calls.