Browsing by Author "Chang, Ming-Feng"

Now showing 1 - 17 of 17

A callback mechanism for Private Telecommunications Networks
(2010-03-15)
Chang, Ming-Feng
;
Lu, Fang-Sun
;
Chia, Chung-Yung
;
資訊工程學系
;
Department of Computer Science
Private Telecommunications Networks (PTNs), such as enterprise telephony and Voice over IP (VoIP), have been widely deployed. A common limitation of PTNs is that PTN users are usually not assigned with Public Switched Telephone Network (PSTN) EA 64 numbers. A PTN user is usually identified by an extension number or a URI (universal resource identifier). When a PTN user initiates a call to a PSTN user, it is not possible to use the PTN calling party's identifier as the caller ID; instead, an E.164 number of the PBX or VoIP gateway is used. As a result, the PSTN called party cannot use the caller ID received to call back to the PTN calling party later, if the PTN user's extension number or URI is unknown. This paper proposes a callback table approach to solve this problem. We describe how the call-out information is stored into and retrieved from a callback table maintained in the PBXs; or VoIP gateways to provide callback service. Numeric analysis has been performed to evaluate the performance of this callback solution. The numeric results indicate that the callback method provides a satisfactory solution when there is sufficient voice traffic served by a VoIP gateway. (C) 2009 Elsevier B.V. All rights reserved.
A flexible organic pentacene nonvolatile memory based on high-kappa dielectric layers
(2008-12-08)
Chang, Ming-Feng
;
Lee, Po-Tsung
;
McAlister, S. P.
;
Chin, Albert
;
電子工程學系及電子研究所
We report a pentacene thin film transistor nonvolatile memory fabricated on a flexible polyimide substrate. This device shows a low program/erase voltage of 12 V, a speed of 1/100 ms, an initial memory window of 2.4 V, and a 0.78 V memory window after 48 h. This has been achieved by using a high-kappa dielectric as charge trapping, blocking, and tunneling gate insulator layers.
An analysis of location record checkpointing interval for mobility database in PCS networks
(2009-11-01)
Chang, Hung-Hsin
;
Chang, Ming-Feng
;
Tseng, Chien-Chao
;
資訊工程學系
;
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.
Analyze the Performance of the Cyclic Indexing Schemes for the Wireless Data Broadcast
(2010-04-01)
Li, Long-Sheng
;
Chang, Ming-Feng
;
Lee, Gwo-Chuan
;
資訊工程學系
;
Department of Computer Science
Wireless data broadcast is an effective approach to disseminate information to a massive number of users. Indexing techniques for broadcasting data can reduce the battery power consumptions of mobile terminals by decreasing the tuning time. The organization of the indexes affects the efficiency of data searching. We investigate how the degree of the index node affects the tuning time, and thus minimize the power consumption of user's terminals. We proposed a performance measurement for the tuning time and a cyclic indexing algorithm. The numerical results suggest the degree of an index node be 3 when the access probabilities of the data tend to be uniformly distributed so that the expected tuning time is minimal. When the access distribution of the data nodes is skewer, the tuning time can be minimized by setting the degree in the index node 2.
Channel allocation for priority packets in the GPRS network
(2006-08-01)
Chia, Chung-Yung
;
Chang, Ming-Feng
;
資訊工程學系
;
Department of Computer Science
As the General Packet Radio Service (GPRS) network begins to provide such as "push-to-talk" (PTT) service, delay-sensitive packets should be given higher priority in transmission. In this paper, we study two channel allocation schemes that implement priority queues for priority packets in the GPRS network: Bitmap Channel Allocation (BCA) and Uplink State Flag Channel Allocation (USFCA). Our study shows that the transmission delay of priority packets in the GPRS network can be better guaranteed using USFCA.
Derivation of Cell Residence Times from the Counters of Mobile Telecommunications Switches
(2011-12-01)
Lin, Yi-Bing
;
Chang, Ming-Feng
;
Huang-Fu, Chien-Chun
;
資訊工程學系
;
Department of Computer Science
In mobile telecommunications, the residence times of users at a cell or a location area are an important input parameter for network planning and performance evaluation of a mobile network. However, measurement of cell residence times in a commercially operated mobile network is not trivial, which typically requires tracing the movement of individual users. In this paper, we show how to use the standard counter values (number of handovers and call traffic) measured in a mobile telecommunications network to derive the cell residence times. These counter values can be obtained directly from telecommunications switches. Therefore, we can provide a quick and simple solution to compute cell residence times.
Deriving the Vehicle Speeds from a Mobile Telecommunications Network
(2013-09-01)
Liou, Ren-Huang
;
Lin, Yi-Bing
;
Chang, Yu-Long
;
Hung, Hui-Nien
;
Peng, Nan-Fu
Vehicle speeds are often measured by intelligent transportation systems (ITSs) by utilizing sensors or software solutions. Our previous work proposed the Lin-Chang-Huangfu (LCH) scheme to compute the cell residence times by the standard counter values in mobile telecommunications switches. In this paper, we use mathematical and statistical developments to investigate the accuracy of the LCH scheme by deriving the bias of the cell residence times computed in this scheme. Then, we extend the LCH scheme with some filtering and compensation techniques for vehicle speed estimation and validate our approach with vehicle detector (VD) measurements at National Highway 3, Longtan Township, Taoyuan County, Taiwan. Our study indicates that the LCH scheme is an effective approach to vehicle speed estimation.
Deriving the Vehicle Speeds from Mobile Telecommunications Network
(2012-01-01)
Liou, Ren-Huang
;
Lin, Yi-Bing
;
Chang, Yu-Long
;
Chang, Ming-Feng
;
資訊工程學系
Vehicle speeds of roads are measured by the Intelligent Transportation Systems (ITS) through some sensors or software solutions. Our previous work proposed the Lin-Chang-Huangfu (LCH) scheme to compute the cell residence times by the standard counter values in the mobile telecommunications switches without any modification to the telecommunications network. In this paper, we extend the LCH scheme and some filtering techniques to estimate the vehicle speeds, and validate our approach with the vehicle detector measurements at National Highway 3, Longtan Township, Taoyuan County, Taiwan. Our study indicates that the LCH scheme can provide accurate vehicle speeds.
Flat-Rate Packet Scheduling for the WCDMA Systems with HSDPA
(2010)
Chia, Chung-Yung
;
Chang, Ming-Feng
;
資訊工程學系
;
Department of Computer Science
To attract more users to use mobile packet services, mobile operators have begun to provide flat-rate packet services in the WCDMA system with High Speed Downlink Packet Access (HSDPA). Since usage does not incur extra cost, flat-rate users may always stay on line and occupy most of the radio channel resources. In this paper, we consider a HSDPA network serving two types of user packets: charged packets (CPs) and flat-rate packets (FRPs). We consider the balance between serving the FRPs and CPs. Four downlink packet scheduling methods were studied in this paper. Our study using Markov process shows that Dynamic Discard Timer for FRPs and Dynamic Guard Slots for CPs methods are more effective in transmitting downlink CPs especially when the downlink FRP traffic is high. Therefore, they are better in guaranteeing the system throughput for CPs, and thus the operator revenue can be better protected.
Inelastic electron tunneling spectroscopy study of ultrathin Al(2)O(3)-TiO(2) dielectric stack on Si
(2010-11-15)
Liu, Zuoguang
;
Cui, Sharon
;
Kornblum, Lior
;
Eizenberg, Moshe
;
Chang, Ming-Feng
We report the properties of an ultrathin Al(2)O(3)-TiO(2) dielectric stack with the equivalent-oxide thickness=1.0 nm. The stack exhibits nondiscernable interfacial layer on Si, and absence of serious Al(2)O(3)-TiO(2) intermixing. Inelastic electron tunneling spectroscopy (IETS) has been used to provide a wealth of information concerning the phonons, bonding vibration modes, and traps in the Al(2)O(3)-TiO(2) gate dielectric stack as well as its interfaces in a metal-oxide-Si structure. The IETS spectra before and after forming gas annealing suggest that the reduction of traps is related to the formation of Si-H bonds at the oxide-Si interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3518478]
Inelastic electron tunneling spectroscopy study of ultrathin Al2O3-TiO2 dielectric stack on Si
(2010-11-15)
Liu, Zuoguang
;
Cui, Sharon
;
Kornblum, Lior
;
Eizenberg, Moshe
;
Chang, Ming-Feng
We report the properties of an ultrathin Al2O3-TiO2 dielectric stack with the equivalent-oxide thickness=1.0 nm. The stack exhibits nondiscernable interfacial layer on Si, and absence of serious Al2O3-TiO2 intermixing. Inelastic electron tunneling spectroscopy (IETS) has been used to provide a wealth of information concerning the phonons, bonding vibration modes, and traps in the Al2O3-TiO2 gate dielectric stack as well as its interfaces in a metal-oxide-Si structure. The IETS spectra before and after forming gas annealing suggest that the reduction of traps is related to the formation of Si-H bonds at the oxide-Si interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3518478]
Method and apparatus for telephone routing between PTN and PSTN
(2007-05-31)
Chang, Ming-Feng
;
Lin, Yi-Bing
;
Liang, Ching-Feng
Disclosed is a method and apparatus applicable to an interface between PSTN and PTN for telephone routing. The interface includes a branch switch, a key system, a network branch switch, and media gateway, etc. The telephone routing method and apparatus of the present invention creates, maintains, and utilizes a call-back routing table to enable a specified PSTN user to call the callback external leased line to reach a specified PTN user in a one-stage dialing manner. The process of one-stage dialing includes PTN call origination to PSTN, PSTN call origination to PTN, and callback tag insertion in the call-back routing table. The call-back routing table consists of a plurality of call-back tags. Each call-back tag consists of at least a data triple, i.e. PTN user identifier, PSTN called party telephone number, and callback leased line identifier.
Performance modeling of integrated mobile prepaid services
(2007-03-01)
Yang, Wei-Zu
;
Lu, Fang-Sun
;
Chang, Ming-Feng
;
資訊工程學系
;
Department of Computer Science
Prepaid personal communication service users have outnumbered postpaid users. This paper studies the charging issues of an integrated Global System for Mobile Communications (GSM) and General Packet Radio Service (GPRS) prepaid service, where a single prepaid account provides a user both voice and data services. The call setup and charging procedures for GSM and GPRS are presented using the Customized Applications for Mobile network Enhanced Logic network architecture. To reduce the probability of terminating both ongoing voice and data calls, we suggest that no new call be admitted when the user credit is below a threshold. An analytic model has been developed to evaluate the performance of the approach. Computer simulations have also been used to verify the results. The numeric results indicate that the force-termination probability can be significantly reduced by choosing an appropriate threshold of the user credit.
Temporary Call-back Telephone Number Service
(2012)
Chang, Ming-Feng
;
Chen, Chi-Hua
;
資訊工程學系
;
Department of Computer Science
Conventional temporary telephone number (TTN) service provides a secondary telephone number to a service subscriber. The subscribers can protect privacy by sharing their TTNs without revealing their private numbers. However, TTN service is rarely provided because it requires a large amount of temporary telephone numbers. In this paper, we present a restricted form of TTN service - temporary call-back telephone number (TCN) service - to reduce the amount of telephone numbers needed. A TCN is assigned only for the communications between a subscriber and the correspondent parties specified by the subscriber. Other users, except for the specified correspondent parties, cannot reach the subscriber through the assigned TCN. A TCN assignment can be specified by a telephone number mapping record that consists of a subscriber's number, a TCN, and a correspondent party's number. A TCN can be assigned to more than one subscriber, as long as the subscribers' specified correspondent parties are different. Analytic models using Markov chains have been developed to show that the TCN service significantly reduces the amount of temporary numbers required. The TCN service can be implemented using the Intelligent Network (IN) service architecture as a value-added service. TCN Subscribers can initiate calls to and receive calls from the specified correspondent parties without revealing their private telephone numbers. However, the TCN service is not a replacement of the conventional TTN service because only the specified correspondent parties can reach the subscriber by the assigned TCN.
The frequency of CFVD speed report for highway traffic
(2015-04-10)
Chang, Ming-Feng
;
Chen, Chi-Hua
;
Lin, Yi-Bing
;
Chia, Chung-Yung
;
資訊工程學系
The control signals of cellular networks have been used to infer the traffic conditions of the road network. In particular, consecutive handover events are being used to estimate the traffic speed. During traffic congestion, consecutive handover events may be rare because vehicles move slowly, and thus very few or no speed reports would be generated from the congested area.However, the traffic speed report rate during traffic congestion has not been investigated in the literature. In this paper, we present an analytic model to estimate the speed report rate from cellular network signaling in steady traffic conditions, that is, the traffic speed and flow are assumed constant. Real field trial data were used to validate our analytic model. In addition, computer simulations were conducted to study how speed reports are generated in dynamic traffic conditions when traffic speed and flow change rapidly. Our study indicates that in a typical cell of length 1.5km with a typical expected call holding time of 1min, no speed report was generated from a congested three-lane highway. Our study demonstrates that the lack of speed reports from consecutive handover events during rush hours indicates severe traffic congestion, and new methods that can estimate traffic speed from cellular network data during severe traffic congestion need to be developed. Copyright (c) 2013 John Wiley & Sons, Ltd.
Uplink Connection Scheduling for Flat-Rate Data Services in the UMTS Network
(2009-06-01)
Chia, Chung-Yung
;
Chang, Ming-Feng
;
資訊工程學系
;
Department of Computer Science
To attract more users to mobile packet services, universal mobile telecommunication system (UMTS) operators have been prompting flat-rate packet services. Since usage does not incur cost, flat-rate users tend to stay online longer and occupy most of the radio channel resources. We consider a UNITS network serving two types of user connections: normal user connections (NUCs) and flat-rate user connections (FRUCs). Our goal is to maximize the revenue of the operator by giving a priority to NUCs over FRUCs without discontenting the flat-rate users, in order not to lose the flat-rate users to other operators. Uplink FRUCs may be asked to subrate or suspend transmission when the radio network is fully utilized. Four combinations of scheduling techniques, including queueing, guard channels (GCs), preemption, and rate adaptation, have been studied, and analytic models using Markov processes were used to evaluate their performances. We proposed a cost function representing the revenue loss due to both blocked NUCs and lost flat-rate users. The system parameters used in our analysis are based on realistic operation data. Our analytic results indicate that the revenue loss can be minimized by using waiting queues (WQs) and preemption. Rate adaptation is ineffective in minimizing the revenue loss because subrated connections are less efficient in using the radio spectrum. GCs for NUCs are unnecessary when a WQ or preemption is used. This paper may be valuable for UMTS operators in serving flat-rate users.