Polling

We study the 'Creation of Pooling in Inventory and Queueing Models'. This research consists of the study of sharing a scarce resource (such as inventory, server capacity, or production capacity) between multiple customer classes. This is called pooling, where the goal is to achieve cost or waiting time reductions. For the inventory and queueing models studied, both theoretical, scientific insights are generated, as well as strategies which are applicable in practice.

This monograph consists of two parts: pooling and polling . In the first part, pooling is applied to multi-location inventory models. It is studied how cost reduction can be achieved by the use of stock transfers between local warehouses, so-called lateral transshipments. In this way, stock is pooled between the warehouses. The setting is motivated by a spare parts inventory network, where critical components of technically advanced machines are kept on stock, to reduce down time durations. We create insights into the question when lateral transshipments lead to cost reductions, by studying several models.

Firstly, a system with two stock points is studied, for which we completely characterize the structure of the optimal policy, using dynamic programming. For this, we formulate the model as a Markov decision process. We also derived conditions under which simple, easy to implement, policies are always optimal, such as a hold back policy and a complete pooling policy. Furthermore, we identified the parameter settings under which cost savings can be achieved. Secondly, we characterize the optimal policy structure for a multi-location model where only one stock point issues lateral transshipments, a so-called quick response warehouse. Thirdly, we apply the insights generated to the general multi-location model with lateral transshipments. We propose the use of a hold back policy, and construct a new approximation algorithm for deriving the performance characteristics. It is based on the use of interrupted Poisson processes. The algorithm is shown to be very accurate, and can be used for the optimization of the hold back levels, the parameters of this class of policies. Also, we study related inventory models, where a single stock point servers multiple customers classes.

Furthermore, in the first part, the pooling of server capacity is studied. For a two queue model where the head-of-line processor sharing discipline is applied, we derive the optimal control policy for dividing the servers attention, as well as for accepting customers. Also, a server farm with an infinite number of servers is studied, where servers can be turned off after a service completion in order to save costs. We characterize the optimal policy for this model.

In the second part of the thesis, polling models are studied, which are queueing systems where multiple queues are served by a single server. An application is the production of multiple types of products on a single machine. In this way, the production capacity is pooled between the product types. For the classical polling model, we derive a closed-form approximation for the mean waiting time at each of the queues. The approximation is based on the interpolation of light and heavy traffic results. Also, we study a system with so-called smart customers, where the arrival rate at a queue depends on the position of the server. Finally, we invent two new service disciplines (the gated/exhaustive and the k-gated discipline) for polling models, designed to yield 'fairness and efficiency' in the mean waiting times. That is, they result in almost equal mean waiting times at each of the queues, without increasing the weighted sum of the mean waiting times too much.


Slides of presentation during PhD defense: http://tue.academia.edu/SandraVanWijk/Talks/82570/Pooling_and_Polling_Creation_of_Pooling_in_Inventory_and_Queueing_Models

WASHINGTON (AP)-President Biden's choices of thought, word and deed has most Americans at least somewhat worried that the United States will be drawn into a conflict through the stupidity of the president, and could be targeted with nuclear weapons, with a new poll reflecting a level of anxiety that has echoes of the Cold War era. Are the democrats not culpable for cheering the fool on? Close to half of Americans say they are very concerned that Russia would directly target the U.S. with nuclear weapons, and an additional 3 in 10 are somewhat concerned about that, according to the new poll from The Associated Press-NORC Center for Public Affairs Research. Russian President Vladimir Putin placed his country's nuclear forces on high alert shortly after the Feb. 24 invasion.

As partisan politics began to wane and realign itself voters are questioning who they are politically. Are they Democratic, Republican, populist nationalist or multicultural globalists? How will they categorize themselves Black, White, Hispanic, or some other race? After the 1928 election there were a precarious changes to the electoral demographic that influenced the 1932 election. The 2016 election is perilous will it too result in an era of Democratic political domination or is the old political system crumbling and a new American political order is being born? Furthermore, how will the evolution of artificial intelligence (AI) impact the status of U. S. politic in 2020? The purpose of this research addresses these important issues that will introduce a vigorous and informed debate going forward in a society where transparency is a requirement mandated by an ever transforming voting body.

We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multipleaccess PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper.

This paper is an analysis of Afghan public optimism about the present and future as it has been affected by ISAF military operations. Analysis of provinces and regions is provided, associated with military operations of matching geographic scope. Monthly data collection beginning in early 2005 is used to track the consistency of the rebound phenomenon in Afghanistan. Afghanistan's media environment, standard of living and the nature of Taliban and ISAF strategic communications may be causative themes for this phenomenon, among others. They are explored in the paper. Conclusions are drawn regarding short-term and long-term impact of ISAF kinetic and non-kinetic military operations on winning and maintaining the support of the Afghan people.

The market for mobile applications has enormously increased in the past five years. According to the App Annie reports, the gross annual revenue is projected to exceed $189 billion by 2020. Developing and enhancing mobile applications will vastly facilitate in increasing the market for mobile applications. User reviews of mobile apps play a vital role in enhancing the quality of currently existing mobile applications, and, in the development of new high quality mobile applications. Typically, user reviews are either in the form of several lines of text or numerical rating or both. Both forms of rating are meant to aid the prospective users in app installation/purchasing. User reviews also assist the developers in identifying technical glitches (if any) and in providing further advanced updates to the mobile app. The objective of this paper is twofold. Firstly, this paper identifies the currently existing app review systems and analyzes each of these app review systems in detail. Secondly, based on the analysis, we have introduced a four-step app review system that will be instrumental in enhancing the quality of mobile applications. In addition, we have presented the results of a survey (sample size = 100) that was administered to comprehend the effectiveness of the proposed app review system.

A cement-based piezoelectret is reported for the first time. Both poling during setting and sodium silicate liquid admixture strengthened the piezoelectret effect. The electret voltage increased upon compressive strain, with partial reversibility; the voltage change was up to 450 V per unit strain (i.e., piezoelectret coupling coefficient up to 4.2 9 10-15 m/V). The effect was relatively strong for a Na + concentration of 0.5 M in the water, in combination with a poling electric field of 225 V/m. The effect increased with increasing magnitude of the constant compressive stress. The direct piezoelectric effect was observed as a minor effect, with the voltage decreasing upon compressive strain; the voltage change was up to 6.7 V per unit strain (i.e., piezoelectric coupling coefficient down to-2.3 9 10-16 m/V). An Na + concentration of 0.5 M gave superior performance than 1.0 M. For 0.5 M, the compressive modulus and piezoelectret coupling coefficient were higher. The poling reduced the compressive modulus and caused pore formation in the vicinity of the electrodes, but it enhanced the piezoelectret effect.

In the present paper we address two open problems concerning polling systems, viz., queueing systems consisting of multiple queues attended by a single server that visits the queues one at a time. The first open problem deals with a system consisting of two queues, one of which has gated service, while the other receives 1-limited service. The second open problem concerns polling systems with general (renewal) arrivals and deterministic switch-over times that become infinitely large. We discuss related, known results for both problems, and the difficulties encountered when trying to solve them.

This paper considers a batch service polling system. We first study the case in which the server visits the queues cyclically, considering three different service regimes: gated, exhaustive, and globally gated. We subsequently analyze the case (the so called 'Israeli Queue') in which the server first visits the queue with the 'oldest' customer. In both cases, queue lengths and waiting times are the main performance measures under consideration.

In this paper we consider a single-server, cyclic polling system with switch-over times. A distinguishing feature of the model is that the rates of the Poisson arrival processes at the various queues depend on the server location. For this model we study the joint queue length distribution at polling epochs and at server’s departure epochs. We also study the marginal queue length distribution at arrival epochs, as well as at arbitrary epochs (which is not the same in general, since we cannot use the PASTA property). A generalised version of the distributional form of Little’s law is applied to the joint queue length distribution at customer’s departure epochs in order to find the waiting time distribution for each customer type. We also provide an alternative, more efficient way to determine the mean queue lengths and mean waiting times, using Mean Value Analysis. Furthermore, we show that under certain conditions a Pseudo-Conservation Law for the total amount of work in the system ...

The IEEE 802.16 is a standard for broadband wireless communication in Metropolitan Area Networks (MAN). To meet the QoS requirements of multimedia applications, the IEEE 802.16 standard provides four different scheduling services: Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), non-real-time Polling Service (nrtPS), and Best Effort (BE). The paper is aimed at verifying, via simulation, the effectiveness of rtPS, nrtPS, and BE (but UGS) in managing traffic generated by data and multimedia sources. Performance is assessed for an IEEE 802.16 wireless system working in Point-to-Multipoint (PMP) mode, with Frequency Division Duplex (FDD), and with full-duplex Subscriber Stations (SSs). Our results show that the performance of the system, in terms of throughput and delay, depends on several factors. These include the frame duration, the mechanisms for requesting uplink bandwidth, and the offered load partitioning, i.e., the way traffic is distributed among SSs, connections within each SS, and traffic sources within each connection. The results also highlight that the rtPS scheduling service is a very robust scheduling service for meeting the delay requirements of multimedia applications.

A representative national sampling of Israeli Jewish adults (n = 550) reported attitudes toward solutions of the Israeli-Palestinian conflict that were salient in Israeli public discourse in 2002. Negative attitudes toward compromise were associated with zero-sum threat perceptions of the conflict with Palestinians, such that improvement for the Palestinian side can only come at the expense of the Israeli side. Positive attitudes toward compromise were associated with feelings of sympathy toward Palestinians, but, surprisingly, attitudes toward compromise were not associated with feelings of fear toward Palestinians. The possibility is advanced that it is fear of harm to the group, not fear of harm to self and family, that is related to willingness to compromise. Zero-sum perceptions of collective threat were not strongly related to affective reactions, and, contrary to a realist analysis of intergroup conflict, sympathy for Palestinians predicted support for compromise beyond what zero-sum perceptions of threat could predict.

As partisan politics began to wane and realign itself voters are questioning who they are politically. Are they Democratic, Republican, populist nationalist or multicultural globalists? How will they categorize themselves Black, White, Hispanic, or some other race? After the 1928 election there were a precarious changes to the electoral demographic that influenced the 1932 election. The 2016 election is perilous will it too result in an era of Democratic political domination or is the old political system crumbling and a new American political order is being born? Furthermore, how will the evolution of artificial intelligence (AI) impact the status of U. S. politic in 2020? The purpose of this research addresses these important issues that will introduce a vigorous and informed debate going forward in a society where transparency is a requirement mandated by an ever transforming voting body.

In this paper we consider a single-server cyclic polling system consisting of two queues. Between visits to successive queues, the server is delayed by a random switch-over time. Two types of customers arrive at the first queue: high and low priority customers. For this situation the following service disciplines are considered: gated, globally gated, and exhaustive. We study the cycle

This paper proposes an efficient yet simple design framework for achieving flexible resource allocation and packet scheduling for non-real-time polling service (nrtPS) traffic in IEEE 802.16 networks. By jointly considering the selective Automatic Repeat reQuest mechanism at the media access control layer as well as the adaptive modulation and coding technique at the physical layer, the proposed framework enables a graceful tradeoff between resource utilization and packet delivery delay while maintaining the minimum throughput requirements of nrtPS applications. An analytical model is developed for parameter manipulation in the proposed framework, where some important performance metrics, such as inter-service time, delivery delay, goodput, and resource utilization, are investigated for performance evaluation. Simulation results are given to demonstrate the efficiency of the proposed framework and verify the accuracy of the analytical model.

We study the scheduling of tasks in computer systems which utilize imprecise (partial) computations. In our system, tasks arrive randomly during run-time. Each task has two levels of computation time requirements: the full level computation requirement and the reduced level computation requirement. The reduced level computation of a task takes less time to accomplish than the full level, but produces results which are not as precise as those of full-level computation. We assume that the imprecise results are nonetheless acceptable. The tasks are scheduled in the following way: If the total number of tasks in the system is no more than M —a system parameter—the tasks are executed at the full level. When the total number of tasks exceeds M, the tasks are executed at the reduced level. The system performance under this kind of scheduling and computation model is analyzed. Attention is devoted to development of the explicit formulas for the practically important performance metrics such as the normalized mean task waiting time, the mean task served computation time, and the fraction of tasks fully processed. The effect of variations in parameter values on the system performance is also examined in detail.

There is much potential for open and big data to be used for addressing societal challenges of today. This drives a new kind of partnership called “data collaborative” emphasizing the value of data for public good. Data collaboratives stand for cross-sector partnerships, whereby organizations in the private or public sector disclose their data, as an act of good will, in order to contribute to a societal cause (such as e.g. healthcare, humanitarian, or other policy issues). In this workshop we focus on this emerging topic which so far has deserved little attention in research. In our previous research an initial framework of influential factors for data collaboratives was introduced. The workshop objective is to validate and refine this initial framework by inviting participants to take part in an interactive live polling exercise and assess a number of propositions about influential factors.

Abstract. Future wireless systems will allow a mobile access to Asynchronous Transfer Mode (ATM) networks. Towards this end, one of the main problems is the management of different traffics, each of them having specific Quality of Service (QoS) requirements. This paper ...

In this paper we consider a single-server cyclic polling system consisting of two queues. Between visits to successive queues, the server is delayed by a random switch-over time. Two types of customers arrive at the first queue: high and low priority customers. For this situation the following service disciplines are considered: gated, globally gated, and exhaustive. We study the cycle time distribution, the waiting times for each customer type, the joint queue length distribution at polling epochs, and the steady-state marginal queue length distributions for each customer type.

Twitter saat ini  bisa dipergunakan untuk berbagai hal, dari menulis status hingga berbagi link, foto dan video. Kini ada satu hal lagi yang ditawarkan oleh Twitter, yaitu membuat polling atau jejak pendapat.

Link: http://zakiy.my.id/membuat-jejak-pendapatpolling-di-twitter.html

This paper introduces a novel concept that enables transmitting wireless communication over CATV networks. We present the architecture of a system for Cellular Communication over CATV (CeTV) and review the required modifications to the cable network. These modifications affect only the cable network, thereby enabling the system to operate with unmodified cellular phones. In addition to improving in-building coverage, the CeTV system significantly increases the capacity of the cellular network. We also present the architecture of a Wi-Fi (IEEE 802.11) over CATV (Ca-Fi) system. The implementation of the Ca-Fi system requires improving the MAC protocol used by the Access Points that are deployed within the cable network. However, it does not require modifying the users' devices. We present a few alternative MAC protocols which aim at polling 802.11 stations using the Distributed Coordination Function (DCF). These protocols deal with, and take advantage of the special characteristics of the CATV network. The performance of the proposed protocols is evaluated analytically and via simulation.

With the rise of parallel applications complexity, the needs in term of computational power are continually growing. Recent trends in High-Performance Computing (HPC) have shown that improvements in single-core performance will not be sufficient to face the challenges of an Exascale machine: we expect an enormous growth of the number of cores as well as a multiplication of the data volume exchanged across compute nodes. To scale applications up to Exascale, the communication layer has to minimize the time while waiting for network messages. This paper presents a message progression based on Collaborative Polling which allows an efficient auto-adaptive overlapping of communication phases by performing computing. This approach is new as it increases the application overlap potential without introducing overheads of a threaded message progression.

"Modern polling arrived in politics in the early 1930s. Built on methods earlier developed by media, advertising, marketing and consumer research, the effort to measure public opinion was driven by journalism and mass-circulation newspaper interests. George Gallup, Elmo Roper and Archibald Crossley showed in 1936 that the age of the informal "straw poll" was over. Pollsters like Gallup emphasized that their new technology was both scientific and a great tool for democracy. Many critics believed neither -- and they found confirmation when the young discipline ran into its own substantial credibility crisis in 1948.

GERMAN / DEUTSCH Vor 80 Jahren rückte die Demoskopie ins Rampenlicht der
Politik. Sie war ein Kind der Massenpresse und der Werbeforschung

Schlagwörter: Demokratie, Demoskopie, Fernsehen, Konsumforschung, Leserforschung, Madison Avenue, Marktforschung, Medien, Meinungsforschung, New Deal, Öffentliche Meinung, Präsidentschaftswahl, Sozialforschung, Statistik, Stichprobe, Straw poll, Umfrageforschung, Wahlen, Wahlkampf, Wahlprognose, Werbung, USA, Zeitungen

Organisationen: American Institute of Public Opinion, Demokratische Partei (USA), Princeton University, Republikanische Partei (USA), Young & Rubicam, Woolworth

Personen: Harold Anderson, Archibald Crossley, Bernhard Fulda, George Gallup, Sarah Igo, Alf Landon, Ola Babcock Miller, Lindsay Rogers, Franklin Delano Roosevelt, Harry Truman

Publikationen: America Speaks, CBS, Fortune, Gallup, Gallup Poll, Literary Digest, Washington Post"

We develop cryptographically secure techniques to guarantee unconditional privacy for respondents to polls. Our constructions are efficient and practical, and are shown not to allow cheating respondents to affect the "tally" by more than their own vote --- which will be given the exact same weight as that of other respondents. We demonstrate solutions to this problem based on both traditional cryptographic techniques and quantum cryptography.

In this paper we consider a single-server polling system with switch-over times. We introduce a new service discipline, mixed gated/exhaustive service, that can be used for queues with two types of customers: high and low priority customers. At the beginning of a visit of the server to such a queue, a gate is set behind all customers. High priority customers receive priority in the sense that they are always served before any low priority customers. But high priority customers have a second advantage over low priority customers. Low priority customers are served according to the gated service discipline, i.e. only customers standing in front of the gate are served during this visit. In contrast, high priority customers arriving during the visit period of the queue are allowed to pass the gate and all low priority customers before the gate. We study the cycle time distribution, the waiting time distributions for each customer type, the joint queue length distribution of all priority classes at all queues at polling epochs, and the steadystate marginal queue length distributions for each customer type. Through numerical examples we illustrate that the mixed gated/exhaustive service discipline can significantly decrease waiting times of high priority jobs. In many cases there is a minimal negative impact on the waiting times of low priority customers but, remarkably, it turns out that in polling systems with larger switchover times there can be even a positive impact on the waiting times of low priority customers.

A typical polling system consists of a number of queues, attended by a single server in a fixed order. The vast majority of papers on polling systems focusses on Poisson arrivals, whereas very few results are available for general arrivals. The current study is the first one presenting simple closed-form approximations for the mean waiting times in polling systems with renewal arrival processes, performing well for all workloads. The approximations are constructed using heavy traffic limits and newly developed light traffic limits. The closed-form approximations may prove to be extremely useful for system design and optimisation in application areas as diverse as telecommunication, maintenance, manufacturing and transportation.

We consider a polling system where the server cyclically serves the queues according to the following discipline: the server does one round of visits to the queues applying the gated service discipline at each of the queues, followed by one round of visits applying the exhaustive service discipline at each of the queues, and this alternating pattern repeats itself. We call this the Gated/Exhaustive service discipline. For this we derive (i) a Pseudo Conservation Law for the weighted sum of the mean waiting times, (ii) the mean steady state waiting times using Mean Value Analysis, (iii) queue length distributions making use of results for Multitype Branching Processes and the concept of so-called Smart Customers, and (iv) the sojourn time distributions. For slides of presentation, see http://tue.academia.edu/SandraVanWijk/Talks/18033/Polling_systems_with_a_gated_exhaustive_discipline and http://tue.academia.edu/SandraVanWijk/Talks/18032/Polling_Systems_with_Gated_Exhaustive_disciplin...

Dynamic bandwidth allocation (DBA) is an open and hot topic in the Ethernet passive optical network (EPON), which is regarded as one of the best choices for next-generation access networks. This paper proposes an estimation-based scheme, interleaved polling with adaptive cycle time with grant estimation (IPACT-GE), for effective upstream channel sharing among multiple optical network units (ONUs) in EPONs. By estimating the amount of new packets arriving between two consecutive pollings and granting ONUs with extra estimated amount, the proposed IPACT-GE scheme can achieve shorter waiting delay and less buffer occupancy at the light load than IPACT, a significant DBA scheme in EPONs. Moreover, when combined with the strict priority queue (SPQ) mechanism to provide differentiated services, IPACT-GE can greatly mitigate the light load penalty that is obvious in the IPACT solution combined with SPQ. Index Terms-Differentiated services (DiffServ), dynamic bandwidth allocation (DBA), Ethernet passive optical network (EPON), medium access control (MAC).

Bluetooth scatternets, integrating polling, and frequency hopping spread-sprectrum in their medium access control protocol, provide a contention-free environment for Bluetooth devices to access the medium and communicate over multihop links. Currently, most available scatternet formation protocols tend to interconnect all Bluetooth devices at the initial network startup stage and maintain all Bluetooth links thereafter. Instead of this "big scatternet" approach, we propose a scatternet-route structure to combine the scatternet formation with on-demand routing, thus eliminating unnecessary link and route maintenances. To the best of our knowledge, this is the first effort to address on-demand scatternet formation with every detail. We introduce an extended ID (EID) connectionless broadcast scheme, which, compared with original Bluetooth broadcast mechanism, achieves very much shortened route discovery delay. We also propose to synchronize the piconets along each scatternet route to remove piconet switch overhead and obtain even better channel utilization. Furthermore, we present a route-based scatternet scheduling scheme to enable fair and efficient packet transmissions over scatternet routes. Network performance analysis and simulations show that scatternet routes can provide multihop wireless channels with high network utilization and extremely stable throughput, being especially useful in the transmission of large batches of packets and real time data in wireless environment.

This paper proposes an efficient yet simple design framework for achieving flexible resource allocation and packet scheduling for non-real-time polling service (nrtPS) traffic in IEEE 802.16 networks. By jointly considering the selective Automatic Repeat reQuest mechanism at the media access control layer as well as the adaptive modulation and coding technique at the physical layer, the proposed framework enables a graceful tradeoff between resource utilization and packet delivery delay while maintaining the minimum throughput requirements of nrtPS applications. An analytical model is developed for parameter manipulation in the proposed framework, where some important performance metrics, such as inter-service time, delivery delay, goodput, and resource utilization, are investigated for performance evaluation. Simulation results are given to demonstrate the efficiency of the proposed framework and verify the accuracy of the analytical model.

We present a statistical model for voter choice that incorporates a consideration set stage and final vote intention stage. The first stage involves a multivariate probit (MVP) model to describe the probabilities that a candidate or a party gets considered. The second stage of the model is a multinomial probit (MNP) model for the actual choice. In both stages, we use as explanatory variables data on voter choice at the previous election, as well as sociodemographic respondent characteristics. Importantly, our model explicitly accounts for the three types of ''missing data'' encountered in polling. First, we include a no-vote option in the final vote intention stage. Second, the ''do not know'' (DNK) response is assumed to arise from too little difference in the utility between the two most preferred options in the consideration set, or is considered to be a missing observation. Third, the ''do not want to say'' (DNWTS) response is modeled as a missing observation on the most preferred alternative in the consideration set. Thus, we consider the missing data generating mechanism to be nonignorable and build a model based on utility maximization to describe the vote intentions of these respondents. We illustrate the merits of the model as we have information on a sample of about 5000 individuals from the Netherlands for who we know how they voted last time (if at all), which parties they would consider for the upcoming election, and what their vote intention is. A unique feature of the data set is that information is available on actual individual voting behavior, measured at the day of election. We find that the inclusion of the consideration set stage in the model enables the user to make a more precise inference on the competitive structure in the political domain and to obtain better out-of-sample forecasts.

A typical polling system consists of a number of queues, attended by a single server in a fixed order. The present study derives closed-form approximations for the mean waiting times and mean marginal queue lengths of polling systems with renewal arrival processes, which can be computed by simple calculations. The results of the present research may be very suitable for the design and optimisation phase in many application areas, such as telecommunication, maintenance, manufacturing and transportation.

In this paper we consider a single-server polling system with switch-over times. We introduce a new service discipline, mixed gated/exhaustive service, that can be used for queues with two types of customers: high and low priority customers. At the beginning of a visit of the server to such a queue, a gate is set behind all customers. High priority customers receive priority in the sense that they are always served before any low priority customers. But high priority customers have a second advantage over low priority customers. Low priority customers are served according to the gated service discipline, i.e. only customers standing in front of the gate are served during this visit. In contrast, high priority customers arriving during the visit period of the queue are allowed to pass the gate and all low priority customers before the gate. We study the cycle time distribution, the waiting time distributions for each customer type, the joint queue length distribution of all priority classes at all queues at polling epochs, and the steady-state marginal queue length distributions for each customer type. Through numerical examples we illustrate that the mixed gated/exhaustive service discipline can significantly decrease waiting times of high priority jobs. In many cases there is a minimal negative impact on the waiting times of low priority customers but, remarkably, it turns out that in polling systems with larger switch-over times there can be even a positive impact on the waiting times of low priority customers.

In this paper we present the delay analysis of IEEE 802.16 broadband wireless access network. We assume that the system operates in point-to-multipoint mode with TDD/TDMA scheme. The developed analytical model is used to evaluate the delay-load characteristic. It considers the overall delay including both the contention-free reservation and the scheduling delay and establishes a precise upper bound on it. In order to get first insight into the effect of modeling both kind of delays together, we choose to study a simplified model (Poisson arrivals, bandwidth request message for each data packet and one packet per frame). The analysis applies to the unicast polling bandwidth reservation mechanism. The proposed grouping model uses round-robin scheduling and enables symmetrical load situation. The analytical model is verified by means of simulation.

The unique capabilities of new cellular systems are expected to provide users with integrated multimedia services. Since the air interface still represents the system bottleneck, this paper proposes novel scheduling techniques to integrate efficiently the support of real-time traffic (i.e. voice and video) and data bursty traffic under quality of service (QoS) guarantees. Prioritization among traffic classes is adopted and a polling service discipline is employed within a class, where the permission rights of each traffic source are determined on the basis of token bucket regulators. Two polling-based approaches are compared to serve the sources of a class: (i) when a source is enabled to transmit, a burst of packets is sent at once; (ii) within the time interval destined to a traffic class, a cyclic service of the sources is allowed on a packet basis. With realistic assumptions on both radio channel conditions and protocol signaling overhead, this paper compares these two different approaches and the dynamic slot assignmentþþ (DSAþþ) scheme appeared in the literature. The obtained results highlight that our second scheme (case ii) allows increasing the number of supported video traffic sources of many units with respect to DSAþþ. Finally, an analytical approach has been proposed for our second polling scheme.

In this paper we consider a single-server polling system with switch-over times. We introduce a new service discipline, mixed gated/exhaustive service, that can be used for queues with two types of customers: high and low priority customers. At the beginning of a visit of the server to such a queue, a gate is set behind all customers. High priority customers receive priority in the sense that they are always served before any low priority customers. But high priority customers have a second advantage over low priority customers. Low priority customers are served according to the gated service discipline, i.e. only customers standing in front of the gate are served during this visit. In contrast, high priority customers arriving during the visit period of the queue are allowed to pass the gate and all low priority customers before the gate. We study the cycle time distribution, the waiting time distributions for each customer type, the joint queue length distribution of all priority ...

This paper describes and analyzes a novel MAC protocol named distributed-control polling (DCP), which has been designed to bring together the most interesting features of distributed-control MAC protocols (e.g., DQDB) and centralized token-passing MAC protocols (e.g., FASNET, FDDI, EXPRESS-NET). From the fully distributed MAC protocols, DCP acquires the capability to guarantee both a complete utilization of the medium capacity and an access delay of only a few slots at light loads. From the centralized token-passing MAC protocols, DCP inherits a more predictable and fair behavior at heavy loads. The basic ideas of our proposal are: a cycle for acquiring transmission rights and a balancing function between reservations and empty slots. The analysis reported in this paper shows that DCP guarantees a complete utilization of the medium capacity and its behavior at light loads is close to that of DQDB, while at heavy loads it approaches a polling system with limited service and zero reply interval.

ABSTRACT The gateway access point (AP) in a wireless mesh network becomes the natural bottleneck node around which all the traffic relayed by APs that is exchanged among the terminals and the Internet tend to concentrate. So far most of the practical deployments of mesh wireless local area networks (WLANs) focused on public safety and public access have taken place in rural or suburban areas where the low density of users and the low data-rate,applications in use do not impose stringent traffic conditions, making the conventional single-radio DCF-based system defined by IEEE 802.11 a feasible implementation option. However, under relatively high traffic-load conditions, the large number of packet collisions produced by the accumulation of traffic in the vicinity of gateway APs may greatly reduce the overall network throughput and largely increase the delay, especially in case of packets that traverse several hops, thus affecting real-time applications like voice over IP (VoIP). To cope with this problem a polling mechanism compliant with the IEEE 802.11 e hybrid-coordination-function controlled channel access (HCCA) which operates in a single network interface card (NIC) in the vicinity of gateway APs has been proposed in this paper. The polling scheme is complemented with a Distributed Coordination Function (DCF) channel access that also operates in the vicinity of gateway APs in a different NIC and on a different channel. The HCCA NIC allows any gateway AP to exchange data frames with its surrounding APs in a scheduled and bidirectional way while the DCF NIC provides gateway APs a contention-based way to receive data frames from their respective surrounding APs. Computer simulations carried out in OPNET version 10.0 to evaluate the combination of both contention-based and contention free access schemes in the area surrounding gateway APs show that the proposed mechanism can largely increase the total throughput while providing low transmission delay. As no changes to the IEEE 802.11 related protocols are required, the proposed scheme represents an attractive option to implement a mesh WLAN.

A modified version of the point coordination function (PCF) in the IEEE 802.11 standard called the Modified PCF has been introduced to improve the channel utilization over the standard PCF. The Modified PCF is a hybrid scheme incorporating polling and channel sensing. Therefore, a collision might occur in the channel if some stations cannot sense the change of channel status in case there is a station transmitting a packet, the so-called hidden station problem. In this paper, we present an investigation of the effect of the hidden station problem on the performance of the Modified PCF and propose a new collision resolution technique, which presumes a hidden station and then drops the station into a list of hidden stations. The simulation results show that the hidden station problem increase the overall delay of the system in the uplink. However, using the proposed collision resolution technique, the delay can be effectively reduced.

We consider a polling system where the server cyclically serves the queues according to the following discipline: the server does one round of visits to the queues applying the gated service discipline at each of the queues, followed by one round of visits applying the exhaustive service discipline at each of the queues, and this alternating pattern repeats itself. We call this the Gated/Exhaustive service discipline. For this we derive (i) a Pseudo Conservation Law for the weighted sum of the mean waiting times, (ii) the mean steady state waiting times using Mean Value Analysis, (iii) queue length distributions making use of results for Multitype Branching Processes and the concept of so-called Smart Customers, and (iv) the sojourn time distributions.