Browsing by Author "Haas, ZJ"

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Demand re-registration for PCS database restoration
(2000)
Haas, ZJ
;
Lin, YB
;
資訊工程學系
;
Department of Computer Science
In a Personal Communications Services (PCS) network, mobility databases such as Home Location Register (HLR) and Visitor Location Register (VLR) are utilized to support mobility management for Mobile Stations (MSs). If the location databases fail, the location information loss or corruption will seriously degrade the service offered to the subscribers. In this paper, we propose a new VLR failure recovery scheme called demand re-registration. In this scheme, the VLR broadcasts a re-registration request to all MSs after the VLR failure. When an MS receives the re-registration request, it sends a registration message to the VLR to recover the location record. Since all MSs will re-register after receiving the broadcasting request, traffic jam (and thus collisions) may occur. If a collision occurs, then the involved MSs must re-send the registration messages. This paper studies the performance of demand re-registration by investigating how effectively the re-registration can recover the location record for an MS before the first MS call termination occurs. Our results indicate that demand re-registration can effectively recover VLR failure.
On optimizing the location update costs in the presence of database failures
(1998-01-01)
Haas, ZJ
;
Lin, YB
;
資訊工程學系
;
Department of Computer Science
This paper studies the database failure recovery procedure for cellular phone networks as part of the Electronic Industries Association/Telecommunications Industry Association Interim Standard 41 (EIA/TIA IS-41). Before the location information of the database is recovered, phone calls may be lost. The restoration process can be sped up by having the mobile phones to periodically confirm their existence by radio contact with the cellular network. We show that, under some cost assumptions, periodic update interval should be chosen to be approximately equal to the call interarrival time, with more frequent updates for more unreliable system. We also show that the cost of an optimized system is relatively small and stable, if the system is even moderately reliable. Finally, if the system is at least moderately reliable, the effects of call origination rate and the rate at which Location Areas are crossed are rather small, assuming that the periodic update interval was chosen as stated above. Thus, in such cases, optimization of the size of the Location Area can be made independent of the optimization of the periodic update process.
On optimizing the location update costs in the presence of database failures
(1998-01-01)
Haas, ZJ
;
Lin, YB
;
資訊工程學系
;
Department of Computer Science
This paper studies the database failure recovery procedure for cellular phone networks as part of the Electronic Industries Association/Telecommunications Industry Association Interim Standard 41 (EIA/TIA IS-41). Before the location information of the database is recovered, phone calls may be lost. The restoration process can be sped up by having the mobile phones to periodically confirm their existence by radio contact with the cellular network. We show that, under some cost assumptions, periodic update interval should be chosen to be approximately equal to the call interarrival time, with more frequent updates for more unreliable system. We also show that the cost of an optimized system is relatively small and stable, if the system is even moderately reliable. Finally, if the system is at least moderately reliable, the effects of call origination rate and the rate at which Location Areas are crossed are rather small, assuming that the periodic update interval was chosen as stated above. Thus, in such cases, optimization of the size of the Location Area can be made independent of the optimization of the periodic update process.
TTL prediction schemes and the effects of inter-update time distribution on wireless data access
(2004-09-01)
Fang, YG
;
Haas, ZJ
;
Liang, B
;
Lin, YB
;
資訊工程學系
Modern mobile networks, such as GPRS and UMTS, support wireless data applications. One successful example is the ever popular i-Mode in Japan. Wireless data services ( wireless Internet) become more important as more and more customers of handheld devices enjoy the convenience of the ubiquitous computing. To improve the effective wireless data access, the time-to-live (TTL) management for data entries becomes important due to its use in effective caching design. In this paper, we study three TTL prediction schemes and investigate the effects of the inter-update time distribution on the wireless data access. Performance analysis is carried out via simulations as well as analytical modeling. We expect our results will be useful for the future wireless data access systems, in which transmission power for mobile devices is more limited.