Search

In dynamic wireless networks, nodes move in large-scale spaces with different communications scenarios, including network traffic and unpredicted link state change. However, optimizing multi-user access mechanisms in multiple scenarios to maximize aggregate throughput still remains a practically essential and challenging issue. An efficient method to predict channel conditions and adapt to different communication environments for better performance in real-time is necessary. In this paper, we propose a novel Q-learning based MAC protocol using an intelligent backoff selection scheme to adaptively make decisions by evaluating rewards and variable learning parameters. Furthermore, an efficient channel observation scheme is proposed to optimize real-time decision-making more accurately with better assessment of channel states in different communication environments. Two typical wireless networks, i.e., wireless local area networks with dense users as infrastructure networks and mobile ad hoc networks with changing topologies as infrastructureless networks, are taken into account in simulations to show that the proposed protocol achieves significant performance improvement in terms of both aggregate throughput and packet loss rate with strong environmental adaptability. [ABSTRACT FROM AUTHOR]

The low power wide area networks (LPWANs) based on the LoRaWAN standard are suitable for Internet of Things (IoT) applications that involve a large number of low-power devices distributed over large areas. The LoRaWAN standard imposes some limitations on end-device configuration, such as the medium access strategies to be adopted, which depend on the region in which the network operates. In particular, in Europe, according to the ETSI regulations, a LoRaWAN end-device can use either a pure ALOHA medium access control (MAC) protocol or a polite medium access technique based on Listen Before Talk (LBT) Adaptive Frequency Agility (AFA). The aim of this work is to investigate the combined use of the two MAC protocols in the same LoRaWAN network. In particular, the work presents a simulative assessment of a LoRaWAN network that combines the use of Pure ALOHA and LBT AFA in realistic scenarios, under different workloads, when they work in compliance with the ETSI regulations. The work provides quantitative information that can help the network designer choose which protocol is more suitable for achieving the desired performance. [ABSTRACT FROM AUTHOR]

In this paper, we conduct a survey of the literature about reinforcement learning (RL)-based medium access control (MAC) protocols. As the scale of the wireless ad hoc network (WANET) increases, traditional MAC solutions are becoming obsolete. Dynamic topology, resource allocation, interference management, limited bandwidth and energy constraint are crucial problems needing resolution for designing modern WANET architectures. In order for future MAC protocols to overcome the current limitations in frequently changing WANETs, more intelligence need to be deployed to maintain efficient communications. After introducing some classic RL schemes, we investigate the existing state-of-the-art MAC protocols and related solutions for WANETs according to the MAC reference model and discuss how each proposed protocol works and the challenging issues on the related MAC model components. Finally, this paper discusses future research directions on how RL can be used to enable MAC protocols for high performance. [ABSTRACT FROM AUTHOR]

The low power wide area networks (LPWANs) based on the LoRaWAN standard are suitable for Internet of Things (IoT) applications that involve a large number of low-power devices distributed over large areas. The LoRaWAN standard imposes some limitations on end-device configuration, such as the medium access strategies to be adopted, which depend on the region in which the network operates. In particular, in Europe, according to the ETSI regulations, a LoRaWAN end-device can use either a pure ALOHA medium access control (MAC) protocol or a polite medium access technique based on Listen Before Talk (LBT) Adaptive Frequency Agility (AFA). The aim of this work is to investigate the combined use of the two MAC protocols in the same LoRaWAN network. In particular, the work presents a simulative assessment of a LoRaWAN network that combines the use of Pure ALOHA and LBT AFA in realistic scenarios, under different workloads, when they work in compliance with the ETSI regulations. The work provides quantitative information that can help the network designer choose which protocol is more suitable for achieving the desired performance.

The work presents an extensive simulative assessment of a LoRaWAN network that adopts the Listen Before Talk (LBT) Adaptive Frequency Agility (AFA) channel access technique in compliance with the ETSI regulations. The paper presents the results obtained in several scenarios with a different number of nodes and different configurations of the LoRaWAN Medium Access Control (MAC) parameters. The aim of the paper is to give insights about the performance achievable by changing the configuration parameters. For example, in all the scenarios considered in this work, once the number of nodes is fixed, the impact on the message loss ratio of the considered MAC parameters is always lower than 7%. Conversely, the impact of such parameters on the end-to-end delay is much more significant. The methodology of this assessment is of general validity and can be exploited by the network designer during the network configuration phase to obtain the most suitable combination of the MAC parameters for the network under consideration, based on the number of nodes and the application requirements.

In this paper, we conduct a survey of the literature about reinforcement learning (RL)-based medium access control (MAC) protocols. As the scale of the wireless ad hoc network (WANET) increases, traditional MAC solutions are becoming obsolete. Dynamic topology, resource allocation, interference management, limited bandwidth and energy constraint are crucial problems needing resolution for designing modern WANET architectures. In order for future MAC protocols to overcome the current limitations in frequently changing WANETs, more intelligence need to be deployed to maintain efficient communications. After introducing some classic RL schemes, we investigate the existing state-of-the-art MAC protocols and related solutions for WANETs according to the MAC reference model and discuss how each proposed protocol works and the challenging issues on the related MAC model components. Finally, this paper discusses future research directions on how RL can be used to enable MAC protocols for high performance.

The existence of link correlation has been empirically validated, and different exemplary works exploit the link correlation in the designing of various network protocols. In this work, the authors investigated the impact of this link correlation in contention mechanism of medium access control (MAC). They illustrated negative link correlation could deteriorate the contention mechanism designed to handle hidden terminal problems and, consequently, increase the packet collision rate between the neighbours. They also showed that negative link correlation could increase the chance of an exposed terminal problem. Therefore, ignoring negative link correlation could lead to overestimate overall network throughput and underestimate packet delay. Next, instead of designing a new contention mechanism exploiting the link correlation, they proposed a new routing tree which mitigates the negative effect of negative link correlation without altering the underlying MAC layer. They evaluated this routing tree on Indriya testbed with TelosB nodes and compared it to the minimum spanning tree based on link quality only. The results show improvement in end‐to‐end throughput and packet reception ratio at each node. [ABSTRACT FROM AUTHOR]

The existence of link correlation has been empirically validated, and different exemplary works exploit the link correlation in the designing of various network protocols. In this work, the authors investigated the impact of this link correlation in contention mechanism of medium access control (MAC). They illustrated negative link correlation could deteriorate the contention mechanism designed to handle hidden terminal problems and, consequently, increase the packet collision rate between the neighbours. They also showed that negative link correlation could increase the chance of an exposed terminal problem. Therefore, ignoring negative link correlation could lead to overestimate overall network throughput and underestimate packet delay. Next, instead of designing a new contention mechanism exploiting the link correlation, they proposed a new routing tree which mitigates the negative effect of negative link correlation without altering the underlying MAC layer. They evaluated this routing tree on Indriya testbed with TelosB nodes and compared it to the minimum spanning tree based on link quality only. The results show improvement in end‐to‐end throughput and packet reception ratio at each node. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the performance of MIMO ad hoc networks that employ transmit diversity, as delivered by the Alamouti scheme, and/or spatial multiplexing, according to the Vertical Bell Labs Layered Space-Time system (V-BLAST). Both techniques are implemented in the ns-3 network simulator by focusing on their overall effect on the resulting signal-to-interference-plus-noise ratio (SINR) at the intended receiver. Unlike previous works that have studied fully-connected scenarios or have assumed simple abstractions to represent MIMO behavior, this paper evaluates MIMO ad hoc networks that are not fully connected by taking into account the impact of multiple antennas on the carrier sense activity in CSMA-like medium access control (MAC) protocols. In addition to presenting a performance evaluation of ad hoc networks operating according to each individual MIMO scheme, this paper proposes simple modifications to the IEEE 802.11 DCF MAC to allow the joint operation of both MIMO techniques. Hence, each pair of nodes is allowed to select the best MIMO configuration for the impending data transfer. The joint operation is based on three operation modes that are selected based on the estimated SINR at the intended receiver and its comparison with a set of threshold values. The performance of ad hoc networks operating with the joint MIMO scheme is compared with the performance when using each individual MIMO scheme and the standard single-input single output (SISO) IEEE 802.11. Performance results are presented based on MAC-level throughput per node, delay, and throughput fairness under saturated traffic conditions. [ABSTRACT FROM AUTHOR]

Abstract: Efficient medium access control (MAC) is a key part of any wireless network communication architecture. MAC protocols are needed for nodes to access the shared wireless medium efficiently. Vehicular Ad hoc networks (VANETs) are an emerging network technology on the verge of large-scale deployment. The dynamic network topologies in VANETs caused by high mobility rates of vehicles presents a great challenge in reliable data transfer. A MAC protocol that enables quick reservation of packet transmission slots by vehicles that wish to send packets is crucial in addressing this challenge. In this paper, we propose a new distributed MAC algorithm ResVMAC for VANETs. We demonstrate using simulations, that our algorithm outperforms two state-of-the-art algorithms in key performance metrics. [ABSTRACT FROM AUTHOR]

Energy conservation is a topic of great interest in wireless sensor networks (WSNs). Various techniques have been proposed to minimise the energy consumption. One approach is to design medium access control (MAC) protocols capable of adjusting the sensor node cycle according to the available energy in the battery. The state of charge (SOC) is an indicator of the available energy stored in the battery before discharging. This work proposes a simplified battery model to estimate the SOC and compares the accuracy and computational load of the algorithm as metrics for the implementation of the MAC protocol design. [ABSTRACT FROM AUTHOR]

Wireless sensor networks (WSNs) are considered as the appealing research area. WSNs require highly robust medium access control (MAC) protocol to enhance the performance in several application areas, such as intrusion detection, target detection, industrial automation, environmental monitoring, surveillance system, medical diagnosing system, and tactical system. On the other hand, there are several factors that affect the performance of these applications particularly selection of weak MAC protocol. In this paper, we provide performance impairing drivers for MAC protocols, which affect the efficiency and robustness of MAC protocols in WSN applications. We classify MAC protocols into six categories, as compared with previous MAC surveys that only focused on classifying the MAC protocols into two, three, or four major categories. In addition, we show the link of each category with another based on their existing features. Furthermore, this survey provides a detailed nomenclature in which protocols are categorized based on synchronous and asynchronous communication. This survey also discusses the possible threats and some existing solutions at the MAC layer from 2000 to 2014. Finally, we identify the future research challenges and raise directions for controlling these challenges. [ABSTRACT FROM PUBLISHER]

The need for an efficient medium access control (MAC) protocol is extremely important with the emergence of wireless sensor networks (WSNs). The MAC protocol has increasingly been significant in advancing the performance of WSNs. In this paper, a low duty cycle, energy-efficient and mobility-based Boarder Node Medium Access Control (BN-MAC) hybrid protocol is introduced for WSNs that controls overhearing, idle listening and congestion issues by preserving energy over WSNs. BN-MAC leverages the features of contention and schedule-based MAC protocols. The contention encompasses the novel semi-synchronous approach that helps obtain faster access to the medium. The schedule-based part helps reduce the collision and overhearing problems. The idle listening control (ILC) model is embedded within the BN-MAC that administers the nodes to go to sleep after performing their tasks to saves additional energy. The least distance smart neighboring search (LDSNS) model is used to determine the shortest and most efficient path in a one-hop neighborhood. Evaluation of the BN-MAC is conducted using network simulator-2 (ns2), then its quality of service (QoS) parameters are compared with other known hybrid MAC protocols including X-MAC, Zebra medium access control (Z-MAC), mobility-aware SMAC (MS-MAC), advertisement-based MAC (A-MAC), Adaptive Duty Cycle SMAC (ADC-SMAC) and Mobile Sensor (MobiSense) MAC protocols. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) enable higher safety, enhanced mobility management, and new infotainment services. Currently, the foreseen standard at the medium access control (MAC) layer for VANETs is IEEE 802.11p, which is based on carrier sense multiple access with collision avoidance (CSMA/CA). However, under heavy traffic conditions, CSMA/CA suffers from a high collision probability, particularly in the presence of hidden terminals. Furthermore, the adoption of the request-to-send/clear-to-send (RTS/CTS) mechanism is not effective when a high data rate is required. If high-throughput services are addressed, a new MAC protocol should, thus, be designed. To this aim, in this paper, we propose a new protocol, which is denoted as the orthogonal frequency-division multiple-access (OFDMA)-based MAC protocol for VANETs (OBV), and we compare it with other MAC protocols taken as benchmarks. To verify the feasibility and the performance of the proposed algorithm, we first propose an analytical model in a simplified scenario. Then, we develop exhaustive simulations in realistic scenarios, considering both urban and highway environments. Results show that OBV outperforms all reference protocols, even doubling their throughput under heavy-load network conditions. [ABSTRACT FROM PUBLISHER]

Efficient medium access control (MAC) algorithms are needed for nodes to share a transmission medium and achieve a high throughput. A MAC algorithm schedules packet transmissions so as to that minimize the time taken to send the packets without collisions. In wireless ad hoc and sensor networks, a MAC algorithm must conserve energy as well as provide good throughput. Most existing MAC algorithms for wireless networks are designed to work well under low traffic rates. In this paper we propose a new distributed algorithm Ad-ATMA for wireless ad hoc and sensor networks under relatively high traffic rates. We demonstrate using simulations that Ad-ATMA outperforms the best existing algorithms designed for higher traffic rates in terms of packet delivery ratio and latency while consuming almost identical energy as them. [ABSTRACT FROM AUTHOR]

Opportunistic selection in multi-node wireless systems improves system performance by selecting the “best” node and by using it for data transmission. In these systems, each node has a real-valued local metric, which is a measure of its ability to improve system performance. Our goal is to identify the best node, which has the largest metric. We propose, analyze, and optimize a new distributed, yet simple, node selection scheme that combines the timer scheme with power control. In it, each node sets a timer and transmit power level as a function of its metric. The power control is designed such that the best node is captured even if $\eta$ other nodes simultaneously transmit with it. We develop several structural properties about the optimal metric-to-timer-and-power mapping, which maximizes the probability of selecting the best node. These significantly reduce the computational complexity of finding the optimal mapping and yield valuable insights about it. We show that the proposed scheme is scalable and significantly outperforms the conventional timer scheme. We investigate the effect of $\eta$ and the number of receive power levels. Furthermore, we find that the practical peak power constraint has a negligible impact on the performance of the scheme. [ABSTRACT FROM PUBLISHER]

Opportunistic selection selects the node that improves the overall system performance the most. Selecting the best node is challenging as the nodes are geographically distributed and have only local knowledge. Yet, selection must be fast to allow more time to be spent on data transmission, which exploits the selected node's services. We analyze the impact of imperfect power control on a fast, distributed, splitting based selection scheme that exploits the capture effect by allowing the transmitting nodes to have different target receive powers and uses information about the total received power to speed up selection. Imperfect power control makes the received power deviate from the target and, hence, affects performance. Our analysis quantifies how it changes the selection probability, reduces the selection speed, and leads to the selection of no node or a wrong node. We show that the effect of imperfect power control is primarily driven by the ratio of target receive powers. Furthermore, we quantify its effect on the net system throughput. [ABSTRACT FROM PUBLISHER]

The IEEE 802.16 standard for broadband wireless access has recently been approved. It is an emerging global broadband wireless access standard capable of delivering multiple megabits of shared data throughput supporting fixed, portable, and mobile operation. The standard offers a great deal of design flexibility including support for licensed and licenseexempt frequency bands, channel widths ranging from 1.25 to 20 MHz, Quality of Service (QoS) establishment on a per-connection basis, strong security primitives, multicast support, and low latency/low packet loss handovers. This paper discusses the main features of the various IEEE 802.16 standards with emphasis on the MAC protocol. The focus is on analyzing the differences between MAC layer implementations in several version of the standard like 802.16, 802.16a and 802.16e. This review can be used as the foundation to conduct detailed performance analysis of the emerging WIMAX/802.16 systems.

Owing to its cable‐free deployment, wireless sensor networks (WSNs) have drawn great attention as a new technique for industrial data acquisition. However, the harsh environment of the gas turbine engine provides a number of challenges to deployment of wireless sensors. A definitive study of the impact of harsh environments on WSNs is currently lacking, which represents an obstacle to WSN's deployment in safety‐critical industrial instrumentation and automation. In this study, the authors report the test results of applying WSNs to data acquisition in gas turbine engine testing and the development of a realistic software simulator with the purpose of de‐risking the wireless data transmission technology in a project called WIDAGATE (wireless data acquisition in gas turbine engine testing). This study provides an overview of the simulation platform developed and investigates how small‐scale tests of a WSN deployed on a real engine were used to validate and improve the simulator platform. This work proposes realistic modelling of the physical layer (radio channel) when subject to interference in harsh industry environment during aero‐engine testing. Based on the validated, realistic physical layer model, different medium access control protocols are simulated to demonstrate how this improved simulator can be used to select an appropriate protocol. [ABSTRACT FROM AUTHOR]

During the last few years, bandwidth and traffic control have immerged as issues of great importance in ad-hoc wireless networks, requiring sophisticated managing techniques. Moreover, due to the increasing variety of applications and consequently respective need for bandwidth control, such issues are expected to become even more critical in the near future. Main characteristics of MANETs such as multi-hop communication and supporting dynamically varying topologies rapidly and unpredictably change or remain static over long periods of time augments the complexity of the problem as well as the need to efficiently handle it. In order to circumvent those problems, many researchers turn their attention to cross-layer design which provides the possibility to create lightweight and flexible substrate for the demanding ad-hoc wireless networks. This design approach provides critical features that suit the characteristics of ad-hoc wireless networks. This paper proposes a novel, lightweight and efficient cross-layer architecture for congestion control at wireless ad-hoc networks. The performance of this framework is evaluated considering characteristic ad-hoc routing protocols, such as AODV and DSR, in static as well as mobile network topologies using the well known network simulator NS2. [ABSTRACT FROM AUTHOR]

This paper addresses the flow allocation problem in multi-hop wireless networks. We define and formulate a new interference model, referred to as the Node-based Interference Model, to better capture the behavior of medium access control protocols and the physical layer interference issues. Based on this model, we formulate the problem as a cross-layer network utility maximization problem that considers the coordination of the transport, MAC and physical layers, and avoid the maximum clique or independent set enumeration approach as adopted in most of the existing work. The objective of the problem is to maximize the aggregate network throughput while maintaining the fairness among flows. We then propose a gradient-based flow allocation algorithm by using the duality approach, and analyze the rate of convergence to the optimum for the proposed algorithm. The simulation results show that the proposed algorithm can rapidly converge to the optimum, and can also rapidly adapt to the changes in network topology and routing paths in different flow scenarios. [ABSTRACT FROM PUBLISHER]

We study reducing feedback overhead of users' channel state information required for opportunistic scheduling at a base station while minimizing the throughput penalty incurred due to reduced feedback. We first propose a simple contention based scheme known as 'static splitting' for best effort traffic. The idea is to divide users into static groups, with users that belong to a group, and have their currently supported rate above a threshold, contending to send their current feedback to the base station. This is combined with maximum quantile scheduling -scheduling a user whose current rate is high relative to its distribution, to obtain thresholds that are independent of users' rate distributions even when they are heterogeneous, allowing off-line optimization of thresholds. Next we develop the insight that for a traffic mixture of best effort and real-time traffic one has to combine contention and polling to reduce feedback while providing quality of service. We propose a scheme based on this insight. Under this scheme we prove a lower bound on the service seen by a real-time when users' channel capacities are fast fading. Furthermore, we propose a heuristic modification that is able to exploit a larger fraction of opportunism. Simulation results illustrate the performance advantage of the proposed schemes. [ABSTRACT FROM PUBLISHER]

This paper designs medium access control (MAC) protocols for wireless networks through the network utility maximization (NUM) framework. A network-wide utility maximization problem is formulated, using a collision/persistence-probabilistic model and aligning selfish utility with total social welfare. By adjusting the parameters in the utility objective functions of the NUM problem, we can also control the tradeoff between efficiency and fairness of radio resource allocation. We develop two distributed algorithms to solve the utility-optimal random-access control problem, which lead to random access protocols that have slightly more message passing overhead than the exponential-backoff protocols, but significant potential for efficiency and fairness improvement. We provide readily-verifiable sufficient conditions under which convergence of the proposed algorithms to a global optimality of network utility can be guaranteed, and numerical experiments that illustrate the value of the NUM approach to the complexity-performance tradeoff in MAC design. [ABSTRACT FROM PUBLISHER]

In classical code division multiple access (CDMA) based multi-channel medium access control (MAC) protocols for mobile ad hoc networks (MANETs), numerous exchanges of neighborhood information are required for code assignment such that nodes within a two-hop separation will adopt different transmission codes and therefore avoid the hidden terminal problem (HTP). However, such expensive communication overhead for code assignment is not desirable since it will cause an under-utilization of bandwidth, energy inefficiency and longer delays, which can significantly degrade the network performance. In this paper, a novel location-aware multi-channel MAC protocol is presented for a large-scale dense MANETs based on a scalable two-phase coding scheme, where the first-phase code is used for differentiating adjacent cells and the second-phase code is employed for distinguishing nodes in one specific cell. A node knows its first-phase code from its location information and requests its second-phase code from its cell leaden. This protocol eliminates the HTP during data transmission without the periodical exchange of neighborhood information. Furthermore, the mechanism of collision resolution in the control channel is described. The performance of the proposed protocol is analyzed in terms of the control overhead and delay. The theoretical results are confirmed by extensive simulations and it is shown that the new protocol significantly outperforms the classical CDMA-based multi-channel MAC protocols [ABSTRACT FROM PUBLISHER]

Abstract: In this work, we propose and evaluate mechanisms for the multiplexing and the integrated delivery of various traffic types such as video, data and voice, over a wireless cellular high-speed packet switched network. Two different scenarios are examined where the video traffic results from videoconference sessions and high-quality media playback, respectively. In both cases we focus on the uplink channel and we thoroughly investigate, by using actual MPEG-4 video streams, the system''s performance under a variety of possible loads. Our goal is to achieve high-aggregate channel throughput while preserving the quality of service requirements of each traffic type. [Copyright &y& Elsevier]

Abstract: With rapid development of wireless technology, more and more applications can be served by wireless networks. To provide integrated service over wireless networks has become a very important issue in the design of wireless networks. In this paper, we propose a new MAC protocol with scheduling algorithms to provide integrated service for CDMA based wireless networks. This protocol evolves from the distributed queuing random access protocol for CDMA wireless network (DQRAP/CDMA). The proposed protocol has been designed to have an ability to accommodate integrated traffic in the network with effective scheduling schemes. A series of simulation experiments have been carried out to evaluate the performance of the proposed protocol and scheduling algorithms. The results reveal that the proposed protocol with the scheduling performs effectively to the integrated traffic composed of messages with or without time constraints and achieves fairness among different types of traffic. [Copyright &y& Elsevier]

Abstract: The operation of a personal area network, operating under the IEEE Standard 802.15.4 in the beacon enabled mode, is analyzed using the theory of discrete time Markov chains and M/G/1/K queues. The model includes the impact of different parameters such as packet arrival rate, number of stations, station’s buffer size, packet size, and inactive period between the beacons. We have derived several important performance parameters such as probability of access, probability that medium is idle, queue length distribution in the device, and probability distribution of the packet service time. Some important conclusions regarding the implementation of 802.15.4 networks and compatible network devices are outlined. [Copyright &y& Elsevier]

Development of efficient medium access control (MAC) protocols providing both high throughput performance for data traffic and good quality of service (QoS) support for real-time traffic is the current major focus in distributed contention-based MAC protocol research. In this paper, we propose an efficient contention resolution algorithm for wireless local area networks, namely, the fast collision resolution (FCR) algorithm. The MAC protocol with this new algorithm attempts to provide significantly higher throughput performance for data services than the IEEE 802.11 MAC algorithm and more advanced dynamic tuning backoff (DTB) algorithm. We demonstrate that this algorithm indeed resolves collisions faster and reduces the idle slots more effectively. To provide good fairness performance and to support good QoS for real-time traffic, we incorporate the self-clocked fair queueing algorithm and a priority scheme into the FCR algorithm and come up with the real-time FCR (RT-FCR) algorithm, and show that RT-FCR can simultaneously achieve high throughput and good fairness performance for nonreal-time traffic while maintaining satisfactory QoS support for real-time traffic. [ABSTRACT FROM PUBLISHER]

A new medium access control protocol for wavelength division multiplexing (WDM) Star Networks, which is capable of achieving a high performance under bursty traffic conditions, is introduced. According to the proposed protocol, the access of stations to the wavelengths is based on their grouping. A separate set of groups is maintained for each wavelength within the traffic stream. All the groups are granted permission to transmit on the corresponding wavelength in a round-robin fashion. The main objective of the grouping algorithm is to have in each group exactly one station which is ready to transmit on the corresponding wavelength, at any given time. In this way, idle slots and collisions are minimized and a nearly optimal throughput-delay performance is achieved. The grouping of stations is dynamically modified at each time slot according to the network feedback information. Due to the dynamic nature of the grouping algorithm, the protocol is capable of being adapted to the sharp changes of the stations’ traffic. Extensive simulation results are presented which indicate that the proposed protocol achieves a significantly superior performance than other well-known medium access control protocols for WDM Star Networks. [Copyright &y& Elsevier]

This paper introduces a new approach to integrate different types of medium access control (MAC) protocols into a single wavelength-division-multiplexing (WDM) network system. The WDM network is based on a passive star coupler, and the purpose of integrating different MAC protocols is to efficiently accommodate various types of multimedia traffic streams with different characteristics and quality of service demands. Our integrated MAC protocol is termed multimedia wavelength-division multiple-access (M-WDMA). Three types of multimedia traffic streams are considered in this paper: constant-bit-rate traffic and two classes of variable-bit-rate traffic. Accordingly, three tunable transmitters and one fixed home channel receiver are used in the design of each WDM node. The transmitters transmit the three types of multimedia traffic streams in a pipeline fashion so as to overcome the tuning time overhead and to support parallel transmissions of traffic streams that emerge simultaneously. We further incorporate a dynamic bandwidth allocation scheme that dynamically adjusts the portions of bandwidth occupied by the three types of traffic streams according to their demands. Consequently the M-WDMA protocol achieves high utilization and efficiently adapts to the demands of the multimedia streams so as to guarantee their QoS. The performance of the M-WDMA is evaluated through a simple analytical model and extensive discrete-event simulations. It is shown that the M-WDMA can satisfy the QoS requirements of various mixes of multimedia traffic streams even under very stringent requirements. Moreover, we show that the M-WDMA outperforms conventional MAC protocols for WDM networks. As a result, we expect M-WDMA to be a good multimedia MAC candidate protocol for future-generation WDM networks. [ABSTRACT FROM PUBLISHER]

We propose a wireless access mechanism for web traffic packets in an integrated wireless code-division multiple-access system that has both voice and Web traffic. The proposed scheme is a medium-access control layer/link layer (MAC/LL) scheduling algorithm that consists of a two level control: admission control and packet scheduling. The admission control restricts the number of users in the system such that quality-of-service requirements [target signal-to-interference ratio (SIR) and delay] for both voice and Web traffic can be met. The packet scheduling balances the system interference on a slot-by-slot basis such that the target SIRs can be achieved for all users (voice and Web browsing sessions) with a higher scheduling priority for voice. Designing admission control for Web users based on the average offered rate per session is difficult due to the high variations in the offered load generated by heavy tailed distributions for Web traffic. To overcome this problem, we propose an admission control algorithm that adaptively estimates the aggregate average load based on load measurements using a sliding observation window. [ABSTRACT FROM PUBLISHER]

Wireless networks come in force into the market of computer communications. Unfortunately, several standards coexist (e.g., IEEE 802.11, Bluetooth, HomeRF, HIPERLAN), leading to various types of products. The purpose of this article is to present an overview of those standards and to establish a comparative evaluation. We mainly focus on the medium access control protocols and their ability to support the quality of service required by multimedia applications. Those protocols generally support two modes of operation, a random access mode for asynchronous traffic and a polling mode for real-time synchronous traffic. This article analyzes each protocol's ability to support user QoS requirements. [ABSTRACT FROM PUBLISHER]

This paper focuses on the radio resource management in low earth orbit-mobile satellite systems (LEO-MSSs) based on a time division multiple access (TDMA) air interface. A novel demand-assignment medium access control (MAC) protocol, named DRAMA+ ( dynamic resource assignment multiple access-enhanced version), is proposed, where voice and Web traffic sources obtain transmission slots through requests sent by means of a random access phase. The round-trip propagation delay (RTD) of LEO-MSSs prevents an immediate feedback for each transmission attempt. Therefore, the main concern of the DRAMA+ scheme is to realize an efficient access phase. All the transmission requests successfully received at the satellite are managed by an on board scheduler. We have shown that DRAMA+ outperforms other techniques appeared in the literature in terms of voice quality, transmission delays for bursty data traffics and resource utilization. Moreover, a performance analysis of an ideal version of the DRAMA+ scheme has permitted us to prove the potentialities of the proposed DRAMA+ technique. Stability issues have been addressed as well as the impact on the DRAMA+ performance of the LEO satellite constellation RTD value. Copyright © 2002 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fieldbus networks aim at the interconnection of field devices such as sensors, actuators and small controllers. Therefore, they are an effective technology upon which distributed computer-controlled systems (DCCS) can be built. DCCS impose strict timeliness requirements to the communication network. In essence, by timeliness requirements we mean that traffic must be sent and received within a bounded interval, otherwise a timing fault is said to occur. P-NET is a multi-master fieldbus standard based on a virtual token passing scheme. In P-NET each master is allowed to transmit only one message per token visit, which means that in the worst-case the communication response time could be derived considering that the token is fully utilized by all stations. However, such analysis can be proved to be quite pessimistic. In this paper, we propose a more sophisticated P-NET timing analysis model, which considers the actual token utilization by different masters. The major contribution of this model is to provide a less pessimistic, and thus more accurate, analysis for the evaluation of the worst-case communication response time in P-NET fieldbus networks. [ABSTRACT FROM AUTHOR]

Traffic in gigabit LANs is highly bursty. Furthermore, the destinations of packets transmitted by the same station are highly correlated. An adaptive protocol for WDM passive star networks, which is capable of operating efficiently under bursty and correlated traffic, is introduced. According to the proposed protocol, the stations which are granted permission to transmit at each time slot are selected by taking into account the network feedback information. Although the traffic parameters are unknown and time-variable, the bandwidth of each wavelength is allocated to the stations according to their needs. In this way, the number of idle slots is reduced, resulting in a significant improvement in the network throughput. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Robust-WDM is a technique to realize wavelength division multiplexed (WDM) local area networks (LANs) in the presence of laser wavelength drifts. Various medium access control (MAC) protocols have been proposed for Robust-WDM LANs. Among these protocols, the one with Aperiodic Reservation and Lenient Token-Passing control channel (the AR/LTP protocol) is the most promising. We discuss three internetworking strategies for AR/LTP Robust-WDM LANs. The aim is to explore the possibility to scale the AR/LTP Robust-WDM concepts to the metropolitan domain by looking at some basic medium-access arrangements and specifying the advantages and limitations of each. Special Remote Access Nodes (RANs) are proposed to facilitate interconnection. It is shown that by some modifications in the basic AR/LTP local area protocol and by parallel processing of connection requests, commands and control signals, the waiting time performance of a Robust-WDM interconnection can be improved. The improvement would be accomplished at the expense of some control sophistication. Further improvement can be achieved by designing a set of point-to-point links among the RANs of different Robust-WDM stars. In this case, control is relatively simplified, but the design of a RAN is made more complex and expensive. [ABSTRACT FROM AUTHOR]

Next generation internet optical network for regional access using multi-wavelength protocols (NGI ONRAMP) is a pre-competitive consortium sponsored by DARPA. Its mission is to develop architectures, protocols, and algorithms for wavelength division multiplexing (WDM)-based regional access networks that will effectively support the NGI. A reconfigurable WDM test bed is being built to demonstrate some of the key thrusts of the consortium, including dynamic service provisioning and optical flow switching, service protection in the optical domain, medium access control protocols, and network control and management geared for the efficient transport of Internet traffic over WDM networks. The ONRAMP test bed will consist of a feeder network connecting via access nodes to distribution networks on which the end users reside. ONRAMP network reconfiguration is enabled by access nodes that contain both optical and electronic switching components, allowing data traffic to be routed all-optically through the network or to be switched and aggregated by electronic Internet protocol (IP) routers. This paper describes the goals and basic architecture of the ONRAMP test bed, as well as the design, construction, and characterization of the network access nodes. To illustrate test bed operation, we demonstrate optical flow switching over the test bed that achieves Gb/s throughput of TCP data between end user workstations [ABSTRACT FROM PUBLISHER]

To achieve high efficiency and robustness during the node contention process in medium access control (MAC) protocols, a k‐round contention resolution (k‐CR) scheme is devised. Theoretical analysis of its success probability of selecting only one node ps and throughput is also presented. Numerical results show that the k‐CR scheme can achieve higher ps than the k‐round elimination contention (k‐EC) scheme, and higher throughput than the k‐EC and IEEE 802.11 DCF schemes in a wireless local area network environment. [ABSTRACT FROM AUTHOR]