Forced Termination Research Articles

A buffered-bandwidth approach for supporting real-time video streaming over cellular networks

In this paper, we study the admission and bandwidth allocation problems in real-time video streaming in a cellular network. Admission control in a cellular network is a complex issue due to the mobility of the clients, and the additional workload imposed by incoming clients could exceed the network capacity of a cell and seriously degrade the quality of services provided to the resident clients. To minimize the number of forced terminations of real-time video playback, we incorporate the notion of buffered bandwidth in the admission test for handoff client. Using this approach, we can balance the video workload among adjacent cells to minimize the impact of overloading as the result of handoff operations. We also examine techniques to maintain fairness in services especially under overload situations even though the requested videos from various types of clients could generate very different workload. Simulation experiments confirm the effectiveness of our approach compared to widely used schemes.

Handover Optimization in Wireless Microcellular ATM Networks

Microcellular solutions in wireless ATM networks increase the network traffic control as a result of frequent handover requests. The blocking probability or the forced termination probability presents a quality of service criterion for evaluation of certain handover techniques. This paper presents a handover protocol that can avoid cell loss and guarantee cell sequence, and a two layer wireless call admission control is studied, using Markov state diagrams, in order to optimize the performance of wireless ATM networks.

Resource management and QoS control in multiple traffic wireless and mobile Internet systems

AbstractEnd‐to‐end quality of service (QoS) control for multiple traffic in wired networks is carried out through Differentiated services (DiffServ). Edge routers in DiffServ domain classify incoming flows into different per‐hop behavior (PHB) groups and give a policy‐based QoS guarantee to these behavior aggregates. As Internet extends into the wireless and mobile section, different traffic flows should be treated differently not only in wired core network, but also in wireless resource allocations. In this paper, we propose a preemptive priority handoff and adaptive resource allocation scheme. DiffServ PHB groups are mapped into different wireless and mobile QoS classes. Traffic flows are categorized into these classes in order to allow the system to allocate different bandwidth and make resource reservation according to their priorities. Higher priority traffic flows are permitted to preempt lower priority flows in service. Lower ones, on the contrary, can expand their bandwidth into areas reserved for higher priority traffic flows for better resource utilization. We use both analytical model and simulation to evaluate the system performance in terms of blocking probabilities, forced termination probabilities, and delay. The forced termination probability of high priority traffic flows can be decreased significantly by introducing the preemptive priority scheme. Therefore, this scheme can be used in wireless part of the system along with DiffServ to give further guarantee for low delay, low jitter, and low loss services to high priority services. Copyright © 2005 John Wiley & Sons, Ltd.

Performance analysis of a guard channel reservation handoff scheme for wireless and mobile networks using smart antennas†

In this paper, we propose and analyze a novel wireless and mobile network which employs smart antennas. Using smart antenna techniques, the physical channels (frequency, time slot, code or combinations of them) can be reused in the same cell. In the proposed system, the capacity is increased by reusing channels in a cell. The service quality is improved by inherent properties of smart antennas, such as reducing bit error rate (BER), multipath fading etc. We establish the traffic model and provide an analytical model for the proposed system. The system is modeled and analyzed by a two-dimensional Markov chain. A new algorithm is derived to obtain the equilibrium state probabilities. We also investigate the system in terms of the blocking probability of originating calls and the forced termination probability of handoff calls. As we expect, system capacity and performance are highly improved by employing smart antennas. We believe that the proposed system can be a candidate for future wireless and mobile networks to provide service with high capacity and quality.

Performance analysis of a service-dependent handoff scheme in voice/data integrated cellular mobile systems

In this paper, we propose and analyze a service-dependent handoff and channel allocation scheme in voice and data integrated cellular mobile systems, which combines the ideas of “Variable Bandwidth” and “Preemptive Priority” together. In the scheme, voice and data traffic are considered. According to the variations of the offered traffic intensity at each cell, both a voice and a data call in service can occupy a full-rate channel or a half-rate channel. In order to guarantee the Quality of Service (QoS) for both voice and data traffic, channel resources are fairly shared between voice and data calls according to an optimal channel allocation scheme, which minimizes the difference between the average bandwidth of a voice call in service and that of a data call in service. To minimize the forced termination of a voice call, a voice call can preempt a data call in service if all the calls in the channel pool of the current cell are already assigned with half-rate service. The interrupted data call returns back to the queue specially prepared for data traffic. By analysis, we obtain the most important system performance measures. Comparisons with the scheme, which only supports “Preemptive Priority” without “Variable Bandwidth” supporting, shows that if the total arrival rate for originating calls is not very heavy, the new scheme can provide lower blocking probability and forced termination probability for both voice and data traffic, and shorter average total transmission time for a successfully completed data call.

Optimal Call Admission Control for Voice Traffic in Cellular Mobile Communication Networks

We propose a new call admission control (CAC) scheme for voice calls in cellular mobile communication networks. It is assumed that the rejection of a hand-off call is less desirable than that of a new call, for a hand-off call loss would cause a severe mental pain to a user. We consider the pains of rejecting new and hand-off calls as different costs. The key idea of our CAC is to restrict the admission of new calls in order to minimize the total expected costs per unit time over the long term. An optimal policy is derived from a semi-Markov decision process in which the intervals between successive decision epochs are exponentially distributed. Based on this optimal policy, we calculate the steady state probability for the number of established voice connections in a cell. We then evaluate the probability of blocking new calls and the probability of forced termination of hand-off calls. In the numerical experiments, it is found that the forced termination probability of hand-off calls is reduced significantly by our CAC scheme at the slight expense of the blocking probability of new calls and the channel utilization. Comparison with the static guard channel scheme is made.

Application of support vector machines to bandwidth reservation in sectored cellular communications

Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in sectored cellular networks than in traditional cellular systems. An efficient bandwidth reservation mechanism for the neighboring cells is therefore critical in the process of handoff during the connection of multimedia calls to avoid the unwillingly forced termination and waste of limited bandwidth in the sectored cellular communications, particularly when the handoff traffic is heavy. In this paper, a self-adaptive bandwidth reservation scheme, which adopts support vector machines technique, is proposed to reduce the forced termination probability. Meanwhile, a channel-borrowing technique is used to decrease the new call-blocking probability of real-time traffic. The simulation results show that the proposed scheme can achieve superior performance than the representative bandwidth-reserving schemes in sectored cellular networks in the literature when performance metrics are measured in terms of the forced termination probability and the new call- blocking probability.

Performance of a cellular network based on frequency hopping with dynamic channel allocation and power control

A frequency- and time-division multiple-access (F-TDMA)-based mobile radio system using both dynamic channel allocation (DCA) and frequency hopping (FH) is investigated. We propose a new interference adaptive DCA (IA-DCA) algorithm that is suitably designed for a network implementing FH. The role played by the power control algorithm in this DCA-FH context is also investigated. We compare the performance of our proposal to that of fixed channel allocation (FCA) with and without FH and the well-known IA-DCA schemes investigated in the literature in the absence of FH. The performance results show that interesting synergic effects can be obtained in terms of forced termination and user satisfaction probability by using both DCA and FH. The results we show in the paper have been achieved by means of a system-level simulation tool which takes propagation, user mobility, interference, traffic, and channel allocation into account. The advantages of using FH are accounted for by using a suitable analytical model that gives the frame error rate as a function of the carrier-to-interference ratio and the number of hopping frequencies, at link level; this model is taken from the literature where it was presented for FCA, and here it is modified in order to be applicable to the DCA case.

Intelligent Call Admission Control for Wideband CDMA Cellular Systems

In this paper, we propose intelligent call admission control for wideband code-division multiple-access (CDMA) cellular systems to support differentiated quality-of-service (QoS) requirements, guarantee the forced termination probability of handoffs, and maximize the spectrum utilization. The intelligent call admission controller (ICAC) contains a fuzzy call admission processor to make admission decision for a call request by considering QoS measures such as the forced termination (drop call) probability of handoff, the outage probability of all service types, the predicted next-step existing-call interference, the link gain, and the estimated equivalent interference of the call request. The pipeline recurrent neural network (PRNN) is used to accurately predict the next-step existing-call interference, and the fuzzy logic theory is applied to estimate the new/handoff call interference based on knowledge of effective bandwidth method. Simulation results indicate that ICAC achieves system capacity higher than conventional CAC schemes by an amount of more than 10% in both low and high moving speed cases. Moreover, ICAC can cope with the unpredictable statistical fluctuation of wireless multimedia traffic; it always fulfill QoS requirements for all service types and keep the forced termination probability satisfied, while the CAC of multimedia calls (MCAC) and SIR-based CAC with intercell interference prediction (PSIR-CAC) fail to adapt to the variation of traffic conditions.

QOS and call admission control of multimedia traffic in a PCS network

AbstractIn this paper we study the quality of service of integrated voice and data services in a wireless network. The voice traffic is transmitted in circuit‐switched mode and data traffic is transmitted in packet‐switched mode. Voice traffic has high transmission priority and data packets are transmitted only when there are available channels not used by the voice traffic. Otherwise, the data packets wait in a data buffer. We consider two schemes to reduce the forced termination probability for the handoff voice calls. The two schemes are the reserved channel scheme and the queueing priority scheme. We apply a fluid analysis to study the performance of the data buffer under the two handoff schemes and the basic system in which there is no arrangement to reduce the forced termination probability of handoff calls. From this analysis, we derive admission controls for voice traffic as well as for data traffic. This analysis also enables us to conclude that the reserved channel scheme not only is more effective in reducing the forced termination probability of handoff calls, it is also more effective in providing the QOS guarantee for the data traffic. Another contribution of this paper is to develop a perturbation analysis to solve the fluid models efficiently and quickly. Copyright © 2004 John Wiley & Sons, Ltd.

Quality-of-Service Mechanisms in All-IP Wireless Access Networks

In this paper, we focus on resource reservation protocol (RSVP)-based quality-of-service (QoS) provisioning schemes under Internet protocol (IP) micromobility. We consider QoS provisioning mechanisms for on-going RSVP flows during handoff. First, the rerouting of RSVP branch path at a crossover router (CR) at every handoff event can minimize resource reservation delays and signaling overheads, and in turn the handoff service degradation can be minimized. We show that RSVP branch path rerouting scheme could give a good tradeoff between the resource reservation cost and the link usage. Second, the new RSVP reservation can be made along the branch path toward the CR via a new base station in advance, while the existing reservation path is maintained, and in turn the on-going flow can be kept with the guaranteed QoS. We also show that seamless switching of RSVP branch path could provide the QoS guarantee by adaptively adjusting the pilot signal threshold values. Third, during RSVP resource reservation over wireless link, dynamic resource allocation scheme is used to give a statistical guarantee on the handoff success of on-going flows. We finally obtain the forced termination probability of guaranteed service flows, the average system time of best effort flows by using a transition rate matrix approach.

Psychology Interns' Perspectives on the Forced Termination of Psychotherapy

Predoctoral psychology interns (N = 52) at 21 internship sites were surveyed regarding the forced termination of psychotherapy. Forced termination was found to be a common occurrence, but interns gave their supervisors mixed reviews regarding its supervision. For example, half of the respondents described themselves as less than adequately prepared to cope with forced termination. A significant, positive association was discovered between supervisor attention to forced termination and the degree to which interns felt prepared to manage this experience. While most clients involved in forced terminations were transferred to other therapists, the second most frequent outcome was premature termination of therapy. Implications and future research directions are explored.

A Continuous-Time Agency Model of Optimal Contracting and Capital Structure

We consider a principal-agent model in which the agent needs to raise capital from the principal to finance a project. Our model is based on DeMarzo and Fishman (2003), except that the agent's cash flows are given by a Brownian motion with drift in continuous time. The difficulty in writing an appropriate financial contract in this setting is that the agent can conceal and divert cash flows for his own consumption rather than pay back the principal. Alternatively, the agent may reduce the mean of cash flows by not putting in effort. To give the agent incentives to provide effort and repay the principal, a long-term contract specifies the agent's wage and can force termination of the project. Using techniques from stochastic calculus similar to Sannikov (2003), we characterize the optimal contract by a differential equation. We show that this contract is equivalent to the limiting case of a discrete time model with binomial cash flows. The optimal contract can be interpreted as a combination of equity, a credit line, and either long-term debt or a compensating balance requirement (i.e., a cash position). The project is terminated if the agent exhausts the credit line and defaults. Once the credit line is paid off, excess cash flows are used to pay dividends. The agent is compensated with equity alone. Unlike the discrete time setting, our differential equation for the continuous-time model allows us to compute contracts easily, as well as compute comparative statics. The model provides a simple dynamic theory of security design and optimal capital structure.

A self-adaptive bandwidth reservation scheme for sectored cellular communications

Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in sectored cellular networks than in traditional cellular systems. An efficient bandwidth reservation mechanism for the neighboring cells is therefore critical in the process of handoff during the connection of multimedia calls to avoid the unwillingly forced termination and waste of limited bandwidth in the sectored cellular communications, particularly when the handoff traffic is heavy. In this paper, a self-adaptive bandwidth reservation scheme, which employs a neural fuzzy bandwidth-reserving estimator, is proposed to reduce the forced termination probability. Meanwhile, a channel borrowing technique is used to decrease the new call blocking probability of real-time traffic. The simulation results show that our scheme can achieve superior performance than traditional fixed bandwidth-reserving scheme in sectored cellular networks when performance metrics are measured in terms of the forced termination probability and the new call blocking probability.

Traffic control schemes and performance analysis of multimedia service in cellular systems

This paper presents several traffic control schemes for improving the quality of service (QoS) in cellular systems. Traffic control schemes are devised for the efficient use of the limited radio resources with the increasing number of users and multimedia traffic. Both numerical analysis and computer simu- lations are carried out for the performance evaluation in terms of performance measures. Important performance measures of the suggested traffic control schemes such as the blocking probability of new traffic, the forced termination probability of handoff traffic, and the noncompletion probability for four input multimedia streams are investigated. It reveals that a finite queueing scheme for real-time handoff traffic guarantees QoS metrics, such as the blocking probability of new traffic and forced termination probability of handoff traffic, as well as efficient use of radio resources. In this paper, the priority with reserved channel and queue scheme turns out to provide significant performance improvement.

A handover scheme in clustered cellular networks

There are two types of handovers for mobile users in the clustered cellular networks: inter-cluster and intra-cluster handovers. An inter-cluster handover which occurs as a result of mobile user’s migration between clusters gives rise to additional handover delay, because more complex handover mechanism should be performed by mobile network. In this paper, we analyze multi-layered cluster architecture and we study the effect of cluster size on the inter-cluster handover performance. Then we propose a new hard handover scheme for inter-cluster handover. For an inter-cluster hard handover, additional delay is required for new bearer setup and reroute calculation. When a mobile terminal (MT) call crosses a cluster boundary, the proposed scheme performs some preparatory activities before actual handover is requested. It results in fast hard handover. We also analyze its performance and show that it reduces forced termination probability.

Connection caching: model and algorithms

We introduce a theoretical model for connection caching. In our model each host maintains (caches) a limited number of open connections to other hosts. A request may utilize an open connection in which case it is a hit, or it may require to open a new connection in which case it is a miss. Establishment of a new connection may force termination (eviction) of another connection at each of the endpoints. The goal is to serve the request sequence with minimum number of misses. This model differs from the standard caching model as it involves many caches which affect each other: a decision to terminate a connection by one node affects the cache of another node that is forced to accept the termination. Our motivation to study the problem stems from Web applications, namely the transmission of Hyper Text Transfer Protocol (HTTP) messages over persistent Transmission Control Protocol (TCP) connections. We consider both the off-line connection caching problem where the request sequence is given in advance, and the online connection caching problem, where the algorithm has to serve a request when it arrives without knowledge of future requests. In the off-line settings we show that finding the optimal strategy is NP-hard. We also derive natural algorithms from the optimal cache replacement algorithm for standard caching and prove that the miss rate of these algorithms is within a factor of 2 from optimal. In the online setting we study several families of distributed algorithms that can be implemented by running an independent process at each node. The algorithms differ by the amount of communication which they utilize between pairs of hosts engaged in an open connection. We show optimal k-competitive deterministic algorithms that utilize one communication bit per open connection, where k is the size of the largest cache in the network. On the other hand without such communication bit the best algorithms which we describe are only (2 k−1)-competitive. We also analyze what one can gain by using randomization at different levels of allowed communication.

Interim or Intentional Interim©

Should a church seek an Intentional Interim Minister? Brown suggests it should following a long term pastorate of over 7 years, a forced termination, church conflict, or a series of short term pastorates (2–3 years). How does a church find an Intentional Interim Minister? The church should contact its Director of Missions, the Church/Minister Relations office of its Baptist state convention, or the Interim Ministry Network. The church and Intentional Interim Minister should negotiate their mutual responsibilities and expectations.

The Valuation of Employee Stock Options - How Good is the Standard?

This study contributes to the valuation of employee stock options (ESO) in two ways. First, a new pricing model is presented, allowing a major part of calculations to be solved in closed form. It incorporates a vesting period and independent, forced terminations of the contract. Designed with a focus on good replication of empirics, the model fits with given exercise characteristics better than earlier models. In particular, it is able to account for the correlation of the time of exercise and the stock price performance at exercise, suspected of being crucial for the option value. The impact of correlation is weak, however, whereas the average rate of cancellations turns out to play a central role. The second contribution of this paper is an examination to what extent of the current accounting standard of ESO valuation is subject to discretion and potential misspecification. Given my model is true, the standard is a good proxy. Yet, one important input for the standard valuation process is often unobservable at least for outsiders. Using my model as an example of how the accountant's belief on that input could interact with the truth, I show that there is wide latitude in the determination of prices.

Author Index

This paper proposes a new analytical model for the performance evaluation of cellular communication systems. Our model allows more general cases of the distributions of the call time and the cell residence time. Based on the characterization of the call time by a hyper-Erlang distribution, the Laplace transform of the channel occupancy time distribution is derived as a function of the Laplace transform of the cell residence time distribution. In particular, the essential quality of service measure such as the forced termination probability is exactly obtained by using a delayed renewal process. From numerical results, it is shown that the non-exponential model has an obvious difference in performance as compared to exponential models.