An access network design problem with end-to-end QoS constraints

In this paper, we present an access network design problem with end-to-end quality of service (QoS) requirement. The problem can be conceptualized as a two-level hierarchical location-allocation problem on the tree topology with nonlinear side constraints. The objective function of the nonlinear mixed integer programming model minimizes the total cost of switch and fiber cable, while satisfying demand within the prescribed level of QoS. By exploiting the inherent structure of the nonlinear QoS constraints, we develop linearization techniques for finding an optimal solution. Also, we devise an effective exact optimal algorithm within the context of disjunctive constraint generation. We present promising computational results that demonstrate the effectiveness of the proposed solution procedure.     

不确定环境下考虑风险厌恶的生产-分销网络优化模型及试验设计

考虑上游生产和下游需求不确定性，研究了由工厂、分销中心及终端市场构成的生产-分销网络优化设计问题。针对上游生产不确定性，考虑产生故障和无故障两种状态；针对下游市场需求不确定性，考虑其具有低、中和高三种状态。由于生产发生故障可能导致不合格品的产生，进一步考虑了在上游生产环节是否实施产品监测问题。综合网络运作成本和由不确定性导致的绩效风险，建立了由风险厌恶水平和悲观系数刻画的基于均值-条件风险值（CVaR）准则的生产-分销网络两阶段随机规划模型。特别地，针对由网络潜在节点数众多所导致的不确定情景规模过大的问题，采用情景缩减技术进行了情景筛选，降低了所建模型的求解难度。最后，进行了数值计算，分析了相关参数对网络运作绩效的影响，并给出了期望成本和条件风险值两个目标权衡的帕累托有效前沿。进一步，通过回归试验设计检验了决策者风险厌恶水平和悲观系数对所设计的生产-分销网络绩效的影响程度。结果表明，相对于决策者的风险厌恶程度，悲观系数对网络运作绩效的影响更大。     

A demand classification scheme for spare part inventory model subject to stochastic demand and lead time

In this study, we aim to develop a demand classification methodology for classifying and controlling inventory spare parts subject to stochastic demand and lead time. Using real data, the developed models were tested and their performances were evaluated and compared. The results show that the Laplace model provided superior performance in terms of service level, fill rate (FR) and inventory cost. Compared with the current system based on normal distribution, the proposed Laplace model yielded significant savings and good results in terms of the service level and the FR. The Laplace and Gamma optimisation models resulted in savings of 82 and 81%, respectively.     

An Integrated Decision Methodology for Designing and Operating an Air‐Express Courier's Distribution Network*

DHL, an international air‐express courier, has been operating in Hong Kong for many years. In 1998, the new international airport located at a site considerably distant from the old location opened in Hong Kong (HK). Other airport‐related infrastructure facilities have also been developed or are being developed, resulting in major changes in transport structure as well as a shift in customer demand. In this paper a multiyear distribution network is designed for DHL(HK) using an integrated network design methodology, which consists of a macro model and a micro model. The macro model, a mixed 0–1 LP, determines in an aggregate manner the least‐cost distribution network. The micro model, a simulation, evaluates the operational viability and efficacy of the network according to its service coverage and service reliability. We also illustrate how coverage and reliability can be improved via the integrated use of the two models. Extensive discussion on relevant planning and operational issues of an air‐express courier are included. The methodology has been successfully implemented at DHL(HK). It has been used to design the network, to test strategic decisions, and to update the network.     

考虑保鲜努力与增值服务的生鲜电商供应链最优决策与协调

针对一个生鲜电商与一个生鲜供应商组成的供应链，其中生鲜电商负责销售农产品并提供增值服务，而生鲜供应商负责农产品的保鲜配送。考虑保鲜努力与服务水平均会影响生鲜农产品的市场需求，通过构建集中式与分散式下的生鲜电商供应链决策模型，分析了新鲜度需求弹性、服务需求弹性等因素对最优决策的影响，并对比分析了分散式与集中式决策下的最优决策。在此基础上，设计了"收益共享-双向成本分担"契约，通过合理设计契约参数实现了生鲜电商供应链的完美协调与帕累托改进。最后，进一步深入分析了供应链在协调前后的最优决策变化，并用数值算例进行了考察与验证。研究发现：供应链在协调后必然会提高产品新鲜度与服务水平，但可能会导致更低或更高的生鲜农产品销售价格。当新鲜度需求弹性与服务需求弹性较低时，生鲜电商在协调后会制定相对更低的产品价格，实施"优质低价"策略；而在新鲜度需求弹性或服务需求弹性高于某一水平时，生鲜电商在协调后会制定相对更高的产品价格，实施"优质优价"策略。     

公平关切下基于网络平台销售、回收的E-闭环供应链的主导模式研究

在"互联网+"的大环境下,考虑网络平台的公平关切影响,对不同主导模式下的E-闭环供应链的销售、回收进行研究。文章构建了无公平关切制造商主导、无公平关切网络平台主导、考虑公平关切制造商主导、考虑公平关切网络平台主导的E-闭环供应链四种决策模式。针对每种模型,分析了相应的销售价格、服务水平、回收价格和最优利润等决策变量。研究发现：（1）无论网络平台是否考虑公平关切,制造商主导情况下的销售价格、服务水平和制造商利润均高于网络平台主导的情况;（2）闭环供应链的回收价格只与加工成本、回收再造成本和网络平台收取的回收服务佣金有关;（3）公平关切都会使产品销售价格、服务水平和制造商的利润降低;（4）当网络平台主导系统时,公平关切程度较低,网络平台的利润大于制造商主导时的利润,但当公平关切程度较大时,网络平台的利润则小于制造商主导时的利润。（5）当制造商主导系统时,网络平台的利润随其公平关切的程度先增后减。（6）公平关切相当于让利于消费者,且公平关切程度越大,对消费者的让利幅度越大,对制造商越不利。但在实际中,当网络平台主导系统时,网络平台并不会主动进行公平关切,而在制造商主导系统的情况下,网络平台会考虑一定程度的公平关切,或者由于受消费者的信任压力、政府部门的管理要求和竞争等因素的影响,而不得不考虑公平关切问题。文章的研究结论进一步丰富完善了E-闭环供应链的理论基础。     

A Simulation Metamodel for Response-Time Planning*

Field service management continues to be a major challenge for many service organizations as companies are required to provide more service with less resources. Especially in information intense environments, short response times for service calls are essential to avoid disruptions to a business office or production facility. Managers must regularly assess their manpower needs, and ensure that their allocation and operational decisions lead to the best service at the lowest cost. Xerox Corporation provides copiers, duplicators, and printing systems to an international market. Xerox operates a service network consisting of over 30,000 trained service personnel, each allocated to service regions by the service planning staff. Response-time planning involves many challenging problems: requirements planning at the national level, allocation planning at the district level, and operational planning at the team level. Customer service is critical and is commonly measured by response time—the time that elapses from when a service call is placed to when a service engineer begins service. This paper discusses how Xerox Corporation has used simulation models and metamodels to improve response-time planning and field service operations.     

基于工业互联网平台的增值服务收费模式研究

工业互联网平台的增值服务可以给制造商提供数字化转型服务赋能，实现提质降本增效的作用。本文构建包含一个工业互联网平台、一个制造商和一个零售商组成的三级供应链博弈模型，求解基于使用量收费和订阅收费模式下的最优决策。分析不同定价模式下企业数字化转型决策和利润受到增值服务因子、成本降低因子的影响，以及对两种定价模式下的最优决策进行比较。研究显示：存在不同的平台增值服务效果阈值，当服务效果位于不同阈值范围时，平台和制造商将选择订阅收费模式或按使用量收费模式。当平台增值服务效果适中时，平台和制造商都选择订阅收费模式。当平台增值服务效果较低(高)时，平台(制造商)选择基于使用量收费模式，而制造商(平台)选择订阅收费模式。     

考虑渠道权利结构的产品服务能力竞争机制研究——制造商服务视角

本文针对两个制造商和一个零售商构成的产品服务供应链,以制造商提供服务为视角,研究了产品服务能力竞争问题。运用Stackelberg动态博弈,分别从制造商Stackelberg、零售商Stackelberg和垂直纳什三种不同权利结构情形,求解了供应链成员企业的均衡策略。通过分析服务成本与不同渠道权利结构下均衡结果之间的变化关系,提出能够满足不同客户需求特征的产品服务能力竞争策略。结果表明,当价格与服务能力水平都比较低时,RS价格领先型策略能够满足实惠型客户需求;当服务能力水平比较高时,VN服务领先型策略能够满足经济型客户需求;当价格比较高时,MS产品领先型策略能够满足专业型客户需求;当价格与服务能力水平都比较高时,产品服务融合策略能够满足品质型客户需求。最后,结合批发价格、服务能力水平、零售价格与服务成本之间的数值变化关系,分析了产品服务能力竞争策略的有效性。     

一个园区网上的用户信息管理系统

作为一个连入Internet的大型园区网络AMMSNet,用户通过MSProxy2.0作为代理服务器对Internet进行访问,以MSExchange5.5提供邮件服务。在这种模式下,如何对用户的基本信息进行维护管理,对用户的访问实施监控并对其访问信息进行长期保存,完成用户数据流量的统计,实现用户管理的自动化,一直是Internet服务商和企业级网络管理员需要解决的首要问题。本文以某大型园区网络为例,介绍了利用C Builder与SQLServer数据库开发的Internet用户信息管理系统,以实现对用户访问Internet的一系列自动化管理。     

A New Two‐Bin Policy for Inventory Systems with Differentiated Demand Classes

We consider an inventory system under continuous review with two demand classes that are different in terms of service level required (or penalty cost incurred for backordering of demand). Prior literature has proposed the critical level rationing (CLR) policy under which the demand from the lower priority class is backordered once inventory falls below the critical level. While this reduces the penalty cost for the higher demand class, the fill rate achieved for the lower priority demand class gets compromised. In this study, we propose a new class of two‐bin (2B) policy for the problem. The proposed 2B policy assigns separate bins of inventory for the two demand classes. The demand for each class is fulfilled from its assigned bin. However, when the bin intended for the higher demand class is empty, the demand from the higher class can still be fulfilled with the inventory from the other bin. The advantage of the 2B policy is that better fill rates are achieved, especially for the lower demand class. Computational results show that the proposed policy is able to provide a much higher service level for the lower priority class demand without increasing the total cost too much and without affecting the service level for the higher priority class. When a service level constrained optimization problem is considered, the 2B policy dominates the CLR policy when the service level difference for the two classes is not too high or the service levels required for both the classes are relatively lower.     

一类带有限制的网络瓶颈容量扩张问题

在一些物理网络中,当设施（边的容量等）建立后,由于需求增加,需要调整网络的容量来提高服务水平。调整优化的过程中既要考虑扩张成本,同时也要考虑需要调整的总边数,以尽可能小的影响人们的正常生活。本文研究对于一个给定的网络G,已知边e_i的初始容量和单位容量扩张成本,在预算成本和扩张总边数的约束下,如何有效地扩张边的容量至x_i,使得系统的容量最大,即max{min_ei∈T x_i,T是网络G中的生成树。首先求解两个与之相关的模型,然后通过分析两个相关模型与原问题之间的联系与区别,提出了原问题的多项式时间算法。最后,通过算例说明算法的步骤,并分析了不同参数值对系统容量的影响。     

优化设施服务的网络调整费用均衡问题研究

在物流网络中,当服务设施(配送中心、大型超市等)建立后,由于设施服务水平、市场需求等因素发生变化,需要调整物流网络中各个环节的配送时间来优化设施的服务能力。调整优化的过程中既要考虑需求目标、运行费用的同时也需要考虑调整的成本。本文针对该问题,提出了优化设施服务的物流网络调整费用均衡模型,并针对单个设施的树形配送网络结构,通过辅助网络将该问题转化为最小费用流问题,给出了多项式算法。最后,文中给出了算例以及两种费用的均衡分析。     

Freezing the Master Production Schedule Under Demand Uncertainty

Managing the trade-off between achieving a stable master production schedule (MPS) and being responsive to changes in customer requirements is a difficult problem in many firms where providing a high level of customer service is viewed as an important competitive factor. One alternative for managing this trade-off is to freeze an agreed portion of the MPS. This paper investigates the impact of adjustments in the design parameters of MPS freezing methods on two performance measures (MPS lot-sizing cost and stability) under stochastic demand conditions in a rolling planning horizon environment given a service level target. Simulation experiments are reported which indicate that many of the conclusions regarding the design of MPS freezing methods obtained under deterministic demand conditions hold under stochastic demand.     

考虑服务流的产品服务供应链网络均衡模型

产品服务供应链在向客户制造高质量产品的同时，也提供了产品全生命周期的专业服务，服务的嵌入增加了供应链协调的复杂性。考虑产品服务的双重需求，在分析各主体的运作行为的基础上，构建了包括多个制造商和多个销售商的多主体供应链网络；运用变分不等式刻画了制造商层、销售服务集成商层和需求市场的最优运作行为及其达成均衡的条件；最后，通过修正投影算法对数值算例进行了仿真。研究结果表明：产品服务供应链网络中的产品与服务均衡流相互影响，其中，服务水平直接影响到了产品需求；降低产品的售价将有利于服务价格和效益的提升。研究结论进一步印证了在产品服务供应链网络中承载于产品的服务将逐渐成为价值创造的主体。     

需求替代情形下反应能力的价值分析

本文通过对竞争报童模型加以拓展以研究需求替代情形下企业运用反应能力产生的价值。文中考虑了两种不同的需求结构:第一种中企业总需求是竞争双方库存量的分段线性函数,第二种中企业总需求的均值是双方库存水平任意形式的函数。根据需求结构的不同,建立了不同的库存竞争模型并提出了相应的均衡库存策略。基于这些均衡结论,进一步探讨了反应能力的价值。分析表明运用反应能力能在降低企业库存水平的同时提高顾客服务水平。此外,在不同的需求结构下,运用反应能力产生的价值均随可用反应能力以及缺货惩罚成本递增,而随单位反应能力的使用成本递减。     

Traffic regulation with single- and dual-homed ISPs under a percentile-based pricing policy

We investigate how a customer (an enterprise or a large organization), when facing a percentile-based pricing policy, can optimally balance the Internet access cost and the traffic buffering delay penalty by traffic regulation. The problem is referred to as the Optimal Traffic Regulation (OTR) problem. Solutions to various cases of the OTR problem are provided. For a customer with a single-homed ISP, we present optimal solutions to the OTR problem based on dynamic programming for the offline case with a known traffic demand pattern. A real-time traffic scheduling algorithm is proposed to deal with the online case where the traffic demands are different from a given demand pattern. We further extend the dynamic programming model to the case of dual-homed ISPs. Experimental results on the data from an Internet trace confirm the effectiveness of our solutions. Part of the results has been presented in the First International Conference on Scalable Information Systems.     

允许直达的混合轴辐式快递网络规划模型与算法研究

在快递企业的日常运营中,当两个城市之间的快递业务量达到一定规模之后会允许该城市对之间开展直达递送。但是这一规则通常仅在快递网络规划完成之后由相关子公司提请实施。为弥补这一实际规则的局部最优性缺陷,本论文将直达问题纳入网络规划决策,基于全局优化的视角构建了允许直达的混合轴幅式快递网络规划决策模型,设计了相应的求解流程,并对其中的指派关系决策构建了遗传算法。基于国内标杆企业的数值案例计算证明了该决策模型与求解方法的有效性,研究结果还说明,相对于纯轴辐式结构,允许直达的混合轴幅式网络结构有助于降低网络总成本,同时在直达线路上能够有效的降低迂回、提高服务时效性和服务水平。     

互补型闭环供应链的收益共享与成本共担契约协调优化

互联网平台开放、协作和分享的特点改变了传统的商业模式。如何将互联网思维与传统产业相融合,理论界和实业界正在进行理论探索和模式实践,突破线上平台商和线下渠道服务商界限以提高服务效率,解决线上平台服务和逆向回收难的瓶颈。本文针对单一线上平台商-单一线下渠道服务商的闭环供应链系统,探讨双方如何在正向供应链进行收益共享、逆向供应链进行渠道成本分担情境下的产品定价和服务优化决策。通过对比收益共享模型和收益共享-成本共担模型发现,线上平台商将部分收益分给线下服务商的同时,如果能分担线下渠道服务建设投入,将更有利于逆向回收和服务商逆向渠道服务水平的提高。最后,还通过数值分析,验证了分成分担比例对平台商和服务商决策的影响,以及对各决策变量的影响关系机理。     

Bridging the Healthcare Access Divide: A Strategic Planning Model for Rural Telemedicine Network

Balancing access to healthcare and sustaining operational efficiency is a major issue in strategic planning of rural healthcare delivery systems. In this regard, telemedicine is being adopted as a versatile and low cost mechanism for delivering rural healthcare. This article presents a strategic planning model that incorporates different operational and service elements of the rural telemedicine healthcare network. Real‐world data from the rural Black‐belt region in the United States are used in a case study. A novel statistical approach based on decision trees and logistic regression is used to estimate demand of healthcare at the county level. Key issues such as the location of telemedicine health centers, coverage of health services, configuration of medical equipment, and patient travel policies are explored in light of patient demographics, scale of health coverage, and disease prevalence patterns. Results indicate that telemedicine networks can effectively improve healthcare services in rural areas with requisite operational efficiency.