Contention Resolution Mechanism Research Articles

A burst segmentation-deflection routing contention resolution mechanism in OBS networks

One of the key problems to hinder the realization of optical burst switching (OBS) technology in the core networks is the losses due to the contention among the bursts at the core nodes. Burst segmentation is an effective contention resolution technique used to reduce the number of packets lost due to the burst losses. In our work, a burst segmentation-deflection routing contention resolution mechanism in OBS networks is proposed. When the contention occurs, the bursts are segmented according to the lowest packet loss probability of networks firstly, and then the segmented burst is deflected on the optimum routing. An analytical model is proposed to evaluate the contention resolution mechanism. Simulation results show that high-priority bursts have significantly lower packet loss probability and transmission delay than the low-priority. And the performance of the burst lengths, in which the number of segments per burst distributes geometrically, is more effective than that of the deterministically distributed burst lengths.

On the optimization of the contention resolution mechanism for IEEE 802.16 networks

The IEEE 802.16 standard defines a contention bandwidth request mechanism offering QoS-aware broadband access through a wireless medium. According to the standard, the Base Station (BS) is responsible for granting the requests issued by the Subscriber Stations (SSs). The SSs communicate their requests to the BS by placing their requests into the uplink subframe, using the contention period defined within the subframe for this purpose. The size of contention period, defined in minislots, is fixed by the BS on a frame by frame basis. The remaining part of the uplink subframe is used to carry the data frames. A tradeoff between these two periods of the uplink subframe is required for an effective operation of the system. On the contrary, if the size of the contention is shorten below a certain threshold, the SSs may be unable to place their requests within the time required by the end-user applications. In this paper, we introduce an adaptive mechanism of the contention period size. The proposed mechanism takes into account the varying operation conditions of the system by estimating the number of stations that may be placing a request. Simulation results confirm that our proposal outperforms other mechanisms having recently been reported in the literature.

Busy tone contention protocol: a new high‐throughput and energy‐efficient wireless local area network medium access control protocol using busy tone

SUMMARYDesign of an efficient wireless medium access control (MAC) protocol is a challenging task due to the time‐varying characteristics of wireless communication channel and different delay requirements in diverse applications. To support variable number of active stations and varying network load conditions, random access MAC protocols are employed. Existing wireless local area network (WLAN) protocol (IEEE 802.11) is found to be inefficient at high data rates because of the overhead associated with the contention resolution mechanism employed. The new amendments of IEEE 802.11 that support multimedia traffic (IEEE 802.11e) are at the expense of reduced data traffic network efficiency. In this paper, we propose a random access MAC protocol called busy tone contention protocol (BTCP) that uses out‐of‐band signals for contention resolution in WLANs. A few variants of this protocol are also proposed to meet the challenges in WLAN environments and application requirements. The proposed BTCP isolate multimedia traffics from background data transmissions and gives high throughput irrespective of the number of contending stations in the network. As a result, in BTCP, admission control of multimedia flows becomes simple and well defined. Studies of the protocol, both analytically and through simulations under various network conditions, have shown to give better performance in comparison with the IEEE 802.11 distributed coordination function. Copyright © 2011 John Wiley & Sons, Ltd.

A Global Architecture for a Quality of Service Model for Ad Hoc Networks

Hoc mobile Network (AHNs) may include a plurality of mobile nodes each including a wireless communications device with limited communication resources. Achieving QoS (Quality of Service) in AHNs has been an important research topic in the last years. Hence, we are interested in this paper by the proposition of a global architecture for the offer of a QoS model for AHNs users. Our proposition is based on traffic classification and requires metrics definition allowing the expression of the QoS requirements in order to provide differentiated treatment according to traffic classes. One of the major contributions of this paper concerns the proposition of a novel QoS routing protocol based on delay and bandwidth requirements and called QSDB. Then, we are interested by the proposition of a novel contention resolution mechanism allowing an admission control oriented service differentiation mechanism called DS_CAP. Finally, we propose a QoS reservation mechanism for AHNs, called QSRR. The mechanism uses a traffic classification and requires available bandwidth estimation definition. The advantages of our propositions are shown thanks to some simulation results that are detailed in the end of this paper. General Terms

Performance analysis of the Sent-But-Sure strategy for Optical Burst and Packet Switched Networks

This work proposes an analytical model to characterize the performance of a loss-free transmission strategy for Optical Burst and Packet Switched Networks, which ensures that a burst/packet will successfully reach its destination once it has been scheduled in the first link of its path. In this paper this strategy is called Sent-But-Sure (SBS) because it avoids losses in any intermediate node. The SBS strategy combines a routing and wavelength assignment scheme with simple contention resolution mechanisms. As a result, new burst/packet allocation attempts in an intermediate node only contend with bursts/packets in transit coming from a single input link. Moreover, bursts/packets in transit always have priority over bursts/packets whose transmission has not been scheduled yet. These two main features of the SBS strategy allow us to develop an analytical model based on a two-priority M/G/1 queueing model to characterize the network performance.

Performance overview of the quasi-synchronous operation mode in optical burst switching (OBS) networks

Optical burst switching (OBS) is able to operate under both asynchronous and synchronous burst departures. Although the asynchronous approach is generally assumed in OBS owing to its simplicity and low technical requirements, it has been shown that performance improvements, in terms of the overall burst loss probability, can be achieved under synchronous operation. Moreover, when effective contention resolution mechanisms are applied, such improvements are significant. Since perfect synchronization is not a viable solution, we propose a novel operation mode with relaxed technical requirements, the quasi-synchronous (QS) operation. In this paper, the performance of the QS operation mode is evaluated by an exact analytic expression, assuming a Poisson burst arrival process and a single-wavelength scenario. This mathematical analysis is completed with numerical results that validate its accuracy. Furthermore, we tackle the issue of not having well-aligned clock information between network nodes by proposing a novel re-synchronization mechanism for OBS networks. Finally, a performance study of the QS operation under different deflection routing techniques is presented. The results show that our novel QS approach achieves significant performance benefits with respect to the asynchronous operation while avoiding the architectural complexity of the synchronous scheme.

Analysis and Enhancement of BWR Mechanism in MAC 802.16 for WIMAX Networks

WiMAX [Worldwide Interoperability for Microwave Access] is the latest contender as a last mile solution for providing broadband wireless Internet access and is an IEEE 802.16 standard. In IEEE 802.16 MAC protocol, Bandwidth Request (BWR) is the mechanism by which the Subscriber Station (SS) communicates its need for uplink bandwidth allocation to the Base Station (BS). The performance of the system is affected by the collisions of BWR packets in uplink transmission, that have the direct impact on the size of the contention period in uplink sub frame, uplink access delay and uplink throughput. This paper mainly deals with Performance Analysis and Improvement of Uplink Throughput in MAC 802.16 by the Application of a New Mechanism of Circularity. The implementation incorporates a generic simulation of the contention resolution mechanism at the BS. An analysis of the total uplink access delay and also uplink throughput is performed. A new paradigm of circularity is employed by selectively dropping appropriate control packets in order to obviate the bandwidth request collisions, which yields the minimum access delay and thereby effective utilization of available bandwidth towards the uplink throughput. This new paradigm improves contention resolution among the bandwidth request packets and thereby reduces the delay and increases the throughput regardless of the density and topological spread of subscriber stations handled by the BS in the network.

Dynamic resource allocation with service guarantees over large scale optical networks

The lack of effective contention resolution mechanisms in the optical domain presents dynamic optical switching architectures with a hard dilemma between high loss (when adopting one-way reservations) and high delay (when using two-way reservations). In this work we evaluate an alternative hierarchical network architecture, which achieves a satisfactory compromise by partitioning the network into a number of geographically limited domains operating in slot and frame synchronous mode where two-way reservations are effective.

Bootstrapping a hop-optimal network in the weak sensor model

Sensor nodes are very weak computers that get distributed at random on a surface. Once deployed, they must wake up and form a radio network. Sensor network bootstrapping research thus has three parts: One must model the restrictions on sensor nodes; one must prove that the connectivity graph of the sensors has a subgraph that would make a good network; and one must give a distributed protocol for finding such a network subgraph that can be implemented on sensor nodes. Although many particular restrictions on sensor nodes are implicit or explicit in many papers, there remain many inconsistencies and ambiguities from paper to paper. The lack of a clear model means that solutions to the network bootstrapping problem in both the theory and systems literature all violate constraints on sensor nodes. For example, random geometric graph results on sensor networks predict the existence of subgraphs on the connectivity graph with good route-stretch, but these results do not address the degree of such a graph, and sensor networks must have constant degree. Furthermore, proposed protocols for actually finding such graphs require that nodes have too much memory, whereas others assume the existence of a contention-resolution mechanism. We present a formal Weak Sensor model that summarizes the literature on sensor node restrictions, taking the most restrictive choices when possible. We show that sensor connectivity graphs have low-degree subgraphs with good hop-stretch , as required by the Weak Sensor model. Finally, we give a Weak Sensor model-compatible protocol for finding such graphs. Ours is the first network initialization algorithm that is implementable on sensor nodes.

Contention resolution mechanisms for asynchronous optical packet switching based high performance computing system

We propose an asynchronous optical packet switching (AOPS) based multistage interconnection network employing the distributed control and banyan-like routing scheme, which can construct the high performance computing system (HPCS). A flexible, low latency, and high capacity recycling-fiber-delay-line (Rec-FDL) based collision resolution mechanism is proposed with higher switching efficiency for burst services than that by the conventional packet retransmission algorithm (C-PRA). The system performances, including stability, blocking rate (BR), and longest packets waiting latency (LPWL) are analyzed. The simulation shows that the system stability condition for the Rec-FDL mechanism is the new packet arriving rate ? less than 30×106 packets/s. In addition, the BR and Rec-FDL induced LPWL are 0.1235---0.1413 and 6.305 ns---7.651 ns, respectively, with increasing the number of CPUs connected to the system from 4 to 16,384, while the increment for LPWL induced by the conventional algorithm is 3.9 ns at the same conditions as above. Therefore, the mechanism presented here is more beneficial for the system scalability and has higher latency reducing abilities than the C-PRA.

Load-balanced wavelength assignment strategies for optical burst/packet switching networks

Loss-free schemes are defined to ensure successful packet/burst transmissions in optical packet/burst switching networks. To this end, they rely on a collision-free routing and wavelength assignment (CF-RWA) scheme combined with simple contention resolution mechanisms that guarantee the absence of losses in intermediate links. Here, the CF-RWA problem is studied. In particular, by using graph theory, the problem of finding CF-RWA schemes that minimise the number of wavelengths to serve a given traffic matrix is set. The problem is simplified when it is formulated by using pre-defined sets of non-colliding paths. Within this framework, the problem is shown to be equivalent to finding a given vertex-set colouring of the so-called restriction digraph. Here, two heuristic algorithms are proposed to obtain such vertex-set colourings. One of them provides a suitable CF-RWA without having to solve the minimisation problem. By way of example, the proposed method is applied to the NSFNet and the EON network providing quasi-optimal results.

Comparison and Evaluation of the T-Lohi MAC for Underwater Acoustic Sensor Networks

This paper introduces T-Lohi, a new class of distributed and energy-efficient media-access protocols (MAC) for underwater acoustic sensor networks (UWSN). MAC design for UWSN faces significant challenges. For example, acoustic communication suffers from latencies five orders-of-magnitude larger than radio communication, so a naive CSMA MAC would require very long listen time resulting in low throughput and poor energy efficiency. In this paper, we first identify unique characteristics in underwater networking that may affect all MACs, such as space-time uncertainty and deafness conditions. We then develop T-Lohi employing a novel tone-based contention resolution mechanism that exploits space-time uncertainty and high latency to detect collisions and count contenders, achieving good throughput across all offered loads. T-Lohi exploits a low-power wake-up receiver to significantly reduce energy consumption. We evaluate design choices and protocol performance through extensive simulation. Finally, we compare T-Lohi against a few canonical MAC protocols. The results show that the energy cost of packet transmission is within 3-9% of optimal, and that Lohi achieves good channel utilization, within 30% utilization of the theoretical maximum. We also show that Lohi is stable and fair under both low and very high offered loads. Finally, we compare Lohi with other alternatives, including TDMA, CSMA, and ALOHA. Except for TDMA under heavy load, Lohi provides the best utilization in all cases, and it is always the most energy efficient.

Enhancing Wireless Medium Access Control Layer Misbehavior Detection System in IEEE 802.11 Network

Wireless Medium Access Control (MAC) protocols such as IEEE 802.11 use distributed contention resolution mechanisms for sharing the wireless channel. In this environment, selfish hosts that fail to adhere to the MAC protocol may obtain an unfair throughput share. For example, IEEE 802.11 requires hosts competing for access to the channel to wait for a

Enhancing IEEE 802.11 Random Backoff in Selfish Environments

Wireless access protocols currently deployed in mobile ad hoc networks use distributed contention resolution mechanisms for sharing the wireless channel. In such an environment, selfish hosts that fail to adhere to the medium access control (MAC) protocol may obtain an unfair share of the channel bandwidth at the expense of performance degradation of well-behaved hosts. We present a novel access method, called predictable random backoff (PRB), that is capable of mitigating the misbehavior of selfish hosts, particularly hosts that deliberately do not respect the random deferment of the transmission of their packets. PRB is based on minor modifications of the IEEE 802.11 binary exponential backoff (BEB) and forces each node to generate a predictable backoff interval. The key idea is to adjust, in a predictable manner, the lower bound of the contention window to enhance the per-station fairness in selfish environments. Hosts that do not follow the operation of PRB are therefore easily detected and isolated. We present an accurate analytical model to compute the system throughput using a 3-D Markov chain. We evaluate the performance of PRB under the normal case and in the presence of selfish hosts. Our results show that PRB and BEB similarly perform in the former case. Selfish hosts, however, achieve substantially higher throughput than well-behaved hosts under BEB. PRB, on the other hand, can effectively enhance IEEE 802.11 BEB by mitigating the impacts of these MAC selfish misbehaviors and guarantee a fair share of the wireless channel for well-behaved hosts.

On burst-header contention-resolution in OBS networks

Advances in enabling technologies and the explosive growth of Internet traffic has led to the widespread proliferation of network systems in recent years. With their relatively low cost, high throughputs, high-bandwidth utilization, and low-transmission latency, Optical Burst Switching (OBS) networks represent an ideal solution for next-generation Internet applications. However, in OBS networks, Burst Header Packet (BHP) contentions occur when two or more BHPs are switched simultaneously to the same output port of a given core node. These contention events result in significant losses of the corresponding data burst. Accordingly, this study presents a Store-and-forward COntention-REsolution mechanism, designated as SCORE, which utilizes fiber delay line buffers to resolve the BHP collision problem, thereby minimizing the burst loss rate. The results of a series of simulations performed using an OIRC OBS-ns simulator confirm the effectiveness and efficiency of the proposed scheme.

Inducing Multiscale Clustering Using Multistage MAC Contention in CDMA Ad Hoc Networks

This paper proposes a new principle for designing MAC protocols for CDMA-based ad hoc networks - inducing spatial clustering in contending transmitters/receivers. We first highlight the advantages of CDMA in handling quality of service (QoS) requirements, enhancing energy efficiency, and enabling spatial multiplexing of bursty traffic. Then, based on stochastic geometric models and simulation, we show how idealized contention resolution among randomly distributed nodes results in clustering of successful transmitters and receivers, in turn leading to efficient spatial reuse. This motivates the central idea of the paper which is to explicitly induce clustering among contending nodes to achieve even better spatial reuse. We propose two distributed mechanisms to realize such clustering and show substantial capacity gains over simple random access/ALOHA-like and even RTS/CTS-based protocols. We examine under what regimes such gains can be achieved, and how clustering and contention resolution mechanisms should be optimized to do so. We propose the design of ad hoc networks supporting hop-by-hop relaying on different spatial scales. By allowing nodes to relay beyond the set of nearest neighbors using varying transmission distances (scales), one can reduce the number of hops between a source and destination so as to meet end-to-end delay requirements. To that end we propose a multi-scale MAC clustering and power control mechanism to support transmissions with different ranges while achieving high spatial reuse. The considerations, analysis and simulations included in this paper suggest that the principle of inducing spatial clustering in contention has substantial promise towards achieving high spatial reuse, QoS, and energy efficiency in CDMA ad hoc networks.

On the cross-layer interactions between congestion and contention in wireless sensor and actor networks

Wireless Sensor and Actor Networks (WSAN) are composed of large number of sensor nodes collaboratively observing a physical phenomenon and relatively smaller number of actor nodes, which act upon the sensed phenomenon. Due to the limited capacity of shared wireless medium and memory restrictions of the sensor nodes, channel contention and network congestion can be experienced during the operation of the network. In fact, the multi-hop nature of WSAN entangles the level of local contention and the experienced network congestion. Therefore, the unique characteristics of WSAN necessitate a comprehensive analysis of the network congestion and contention under various network conditions. In this paper, we comprehensively investigate the interactions between contention resolution and congestion control mechanisms as well as the physical layer effects in WSAN. An extensive set of simulations are performed in order to quantify the impacts of several network parameters on the overall network performance. The results of our analysis reveal that the interdependency between network parameters call for adaptive cross-layer mechanisms for efficient data delivery in WSAN.

Analysis and implementation of look-ahead window contention resolution with QoS support in optical burst-switched networks

Optical burst switching (OBS) has been proposed as a promising switching technology to support the next-generation optical Internet. Two critical issues in OBS networks are designing effective contention resolution algorithms and implementing such algorithms in the core switch node. The first part of this paper deals with the problem of contention in OBS networks. We introduce a new contention resolution algorithm called Lookahead window Contention Resolution (LCR) that can support service differentiation. Through complexity analysis, a number of important properties of LCR and its variations are examined and verified. We also investigate the performance of LCR in a single core switch node. We show through simulation that the performance of LCR is competitive to existing contention resolution mechanisms in terms of reducing burst loss. The second part of this paper presents a practical design approach for a generic control packet processor architecture. Based on the proposed architecture, we implement the look-ahead contention resolution algorithm using a high-density field-programmable gate arrays (FPGA). Through hardware test and verification, we evaluate the performance characteristics of the look-ahead contention resolution algorithm in terms of hardware speed, scalability, and cost.

Modeling and performance analysis of IP access interface in optical transmission networks with packet switching

The article analyzes the influence of the Internet Protocol (IP) access interface on the packet loss probability and delay times in the optical packet switched network. The network and node model have been proposed, and the structure of the IP access interface, including assembler and holder, have been included in the analysis. It has been shown that the increase of the maximum optical packet sizes, as well as use of the holding feature as contention resolution mechanism, decrease the packet loss probability, but introduce delays at the optical network access points. Modeling and analysis were based on the discrete event simulation assuming self-similar traffic sources. IP packet lengths were modeled using empirical data.

Performance limitations of the MAC layer in 802.15.4 low rate WPAN

The recent IEEE 802.15.4 standard defines a low rate wireless personal area network which can be used to implement sensor networks. In particular, the beacon enabled mode with slotted CSMA-CA contention resolution mechanism appears suitable for deployment in simple hierarchical sensor clusters. However, a detailed analysis of the operation of the MAC layer according to the 802.15.4 standard reveals a number of issues which may potentially become performance bottlenecks and thus lead to serious performance degradation. we analyze those issues and their impact, and suggest modifications of the coordinator function that allow the network to handle higher traffic loads and thus offer much improved performance to its clients.