Browsing by Author "Chang, Hung-Hsin"

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An analysis of location record checkpointing interval for mobility database in PCS networks
(2009-11-01)
Chang, Hung-Hsin
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Chang, Ming-Feng
;
Tseng, Chien-Chao
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資訊工程學系
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Department of Computer Science
Mobility database that stores the users' location records is very important to connect calls to mobile users on personal communication networks. If the mobility database fails, calls to mobile users may not be set up in time. This paper studies failure restoration of mobility database. We study per-user location record checkpointing schemes that checkpoint a user's record into a non-volatile storage from time to time on a per-user basis. When the mobility database fails, the user location records can be restored from the backup storage. Numeric analysis has been used to choose the optimum checkpointing interval so that the overall cost is minimized. The cost function that we consider includes the cost of checkpointing a user's location record and the cost of paging a user due to an invalid location record. Our results indicate that when user registration intervals are exponentially distributed, the user record should never be checkpointed if checkpointing costs more than paging. Otherwise, if paging costs more, the user record should be always checkpointed when a user registers.
An integrated call agent of the converged VoIP network
(2007-05-01)
Chang, Hung-Hsin
;
Hsu, Meng-Ta
;
Chang, Ming-Feng
;
Tseng, Chien-Chao
;
資訊工程學系
The traditional circuit-switched telecommunication network and the packet-switched data network are converging to a single packet-switched network. One important application of the converged network is telephony communications, also referred to as VoIP (Voice over IP). Call signaling protocols, such as H.323, SIP and MGCP, have been developed to support VoIP communications. To enable devices using different VoIP protocols to communicate, gateways are needed to translate messages of one protocol to messages of another. In this paper, we present a simple, flexible framework for this interworking function. The framework is based on a half-call model where a call is controlled by two half-call finite state machines (FSMs), one representing the state of the caller and the other representing the state of the callee. The interworking function has been implemented such that the caller FSM of one VoIP protocol can interact with the callee FSM of any VoIP protocol. The development effort of the interworking function is minimized since only two half-call FSMs for each VoIP protocol are needed and they can be developed independently as long as the design conforms to the same interface specification. We have developed an integrated call agent (ICA) that contains the half-call FSMs of H.323, SIP and MGCP. Calls between devices using these VoIP protocols can be set up, maintained and terminated by the ICAs.