Browsing by Author "Chen, GC"

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A new locking-based protocol for mobile transactions
(2001)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Due to long network delay of wireless links, transactions will be long-lived transactions in mobile computing environments. In such a situation, the occurrence of handoff is inevitable and thus a wireless link held by a mobile unit crossing cell boundaries might be forced to terminate. It is undesirable that an active transaction is forced to terminate. A queueing scheme has been proposed to solve the problem of forced termination of transactions in our previous research. In the queueing scheme, the execution of a transaction which cannot get a channel when handoff occurs, is suspended and is resumed when it gets a channel again. However when two-phase locking (2PL) protocol is employed, suspending an active transaction will elongate the lock, holding time and thus degrade the system performance. In this paper we propose a new locking-based protocol to improve the performance of 2PL in mobile environments.
An analytic model for performance analysis of concurrency control strategies in mobile environments
(1999-01-01)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Many performance studies have shown that locking based protocols outperform other concurrency control protocols in most database configurations and workloads. However, in mobile environments there are many special characteristics, such as long network delay and the expensive wireless communication. Besides, transactions may be aborted:due to forced termination when handoff occurs for the consideration of concurrency control. The performances of concurrency control strategies should be re-evaluated in such environments, In this paper, we develop an analytic model to evaluate the performances of concurrency control strategies. The accuracy of this model is verified by simulation. According to the experimental results we show that the behavior of mobile users and the degree of data contention have a significant impact on the relative performances of the concurrency control strategies. In particular, we point out that the optimistic concurrency control strategy outperforms other strategies over a wide range of system configurations. We also explain why the optimistic algorithm is well suited in mobile environments.
An analytic model for performance analysis of concurrency control strategies in mobile environments
(1999-01-01)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Many performance studies have shown that locking based protocols outperform other concurrency control protocols in most database configurations and workloads. However, in mobile environments there are many special characteristics, such as long network delay and the expensive wireless communication. Besides, transactions may be aborted:due to forced termination when handoff occurs for the consideration of concurrency control. The performances of concurrency control strategies should be re-evaluated in such environments, In this paper, we develop an analytic model to evaluate the performances of concurrency control strategies. The accuracy of this model is verified by simulation. According to the experimental results we show that the behavior of mobile users and the degree of data contention have a significant impact on the relative performances of the concurrency control strategies. In particular, we point out that the optimistic concurrency control strategy outperforms other strategies over a wide range of system configurations. We also explain why the optimistic algorithm is well suited in mobile environments.
Clustering databases for user location management in PCS network
(1999)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Personal Communication Service (PCS) network is the integration of cellular Network and conventional wired network. To support user mobility, the location information of the mobile stations (MSs) should be constantly tracked using a database. The widespread deployment of PCS will lead to a tremendous increase in the number of updates and queries to the location database. The centralized stand-alone Home Location Register (HLR) in GSM can be a potential bottleneck. Besides, in case of the location database failure, incoming calls may be lost Replicating a HLR cart increase the capacity and reliability of the HLR. However replicating the HLR will cause extra cost because the location update must be executed in each replica. In this paper; we propose a clustering technique to reduce the cost of location updating in replicated HLR. The performance evaluation model is also presented.
Evaluation of distributed and replicated HLR for location management in PCS network
(2003-01-01)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Personal Communication Service (PCS) network is the integration of cellular Network and conventional wired network. To support user mobility, the locations of the mobile stations (MSs) should be constantly tracked using a database. The widespread deployment of PCS will lead to a tremendous increase in the number of updates and queries to the location database. The centralized, stand-alone Home Location Register (HLR) in GSM can be a potential bottleneck. In case of the location database failure, incoming calls may be lost. According to the analysis of the load in HLR, we suggest replicating the HLR in order to increase its capacity and reliability. In this paper we evaluate the effects of the number of replicas in terms of query response time, misrouting probability of incoming calls and average cost per query. Another issue incurred in the replicated databases is data consistency. A concurrency control protocol called preemptive Read-One-Write-All (PROWA) protocol is also proposed.
Modeling the static and dynamic guard channel schemes for mobile transactions
(1998)
Chen, GC
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
There are more and more information services provided on the wireless network. Due to long network delay of wireless link, the transaction will be a long-lived transaction. In such situation, the occurrence of handoff is inevitable, and thus wireless link held by the mobile unit crossing the cell boundaries might be forced to terminate. It is undesirable that an active transaction is forced to terminate. In this paper, we propose two guard channel schemes (GCS), static and dynamic, to reduce the probability of forced termination of transactions. In dynamic GCS, the number of reserved channels of a base station is dynamically assigned according to the number of transaction calls which may handoff to this cell while the number of guard channels is fixed in the static GCS. An analytic model based on Markov chain is derived to evaluate the system performance. The correctness of this model is verified by a simulation program. The experimental results show that a significant improvement is achieved by using the dynamic GCS.