Contention Resolution Scheme Research Articles

Cost-effective combination of contention resolution/avoidance schemes in bufferless slotted OPS networks

Contention is a major problem for Optical Packed Switched (OPS) networks. Many studies have shown that to obtain a very small optical packet loss rate, a large number of specific contention resolution or contention avoidance hardware must be used. However, this may not be so cost-effective. Instead of using the same technique to achieve a very low packet loss rate, the idea of this paper is to use the combination of different contention avoidance and contention resolution schemes, but using a lower amount of each scheme, to reduce packet loss rate in slotted bufferless OPS networks. A number of cost-effective contention resolution and avoidance schemes are studied in order to decrease traffic loss and increase TCP throughput as a result. Designing a multi-fiber architecture that uses inexpensive shared-per-node wavelength converters and additional drop-ports can significantly reduce network-wide traffic loss. The lost traffic can also be retransmitted in the optical domain in order to have a loss-free OPS network. A cost model is also provided to obtain cost-effective combinations of fibers, wavelength converters and drop ports under a desirable TCP throughput and investment on network hardware. The effectiveness of the combined contention avoidance and resolution schemes are demonstrated under Internet traffic.

Fairness and throughput performance of infrastructure IEEE 802.11 networks with hidden-nodes

The fairness behavior and throughput performance of IEEE 802.11 distributed coordination function and request-to-send/clear-to-send channel access scheme in the presence of hidden nodes are investigated. A mathematical model which accurately predicts a user’s throughput performance and packet collision probability in non-saturated traffic and asymmetric hidden node environments is developed. The model allows us to see many interesting results in networks with hidden nodes. In an asymmetric hidden node network environment, the network fairness performance depends on the traffic load. In low traffic conditions, users get their fair share of the resources. However, in moderate-to-high traffic conditions, users that experience less number of hidden nodes dominate the network, causing badly located stations in a network to starve. In addition, the performance of request-to-send/clear-to-send channel access scheme, which is developed as a solution to hidden node problem, in networks with hidden nodes, is also estimated. It is shown that request-to-send/clear-to-send contention resolution scheme greatly improves the network fairness performance in hidden node scenarios. The developed model enables us to more accurately estimate the performance of practical wireless local area networks, where hidden node occurrence is common. Theoretical analysis presented in the paper is validated with simulation results.

Integrated Evaluation of Performance and Technology—Throughput of Optical Burst Switching Nodes Under Dynamic Traffic

In this paper, we introduce an integrated analysis of quality-of-service (QoS) performance and technology for optical burst switching (OBS) nodes. Such an integrated approach is needed to comprehensively assess OBS nodes as both burst losses and signal degradation limit their maximum achievable throughput. We apply this analysis to the tune-and-select (TAS) node architecture as well as to extensions with fiber delay line (FDL) buffers and with limited tuning range converters. First, we discuss OBS and motivate the need for the proposed integrated analysis. We survey contention resolution schemes for OBS and discuss principal QoS performance results for wavelength conversion and FDL buffering. Also, we describe the basic and extended TAS architectures as well as their key physical limitations regarding maximum number of wavelengths and maximum throughput. For the different node architectures, we then present the results obtained in the integrated analysis. We compare them based on the maximum utilization as well as the maximum effective throughput under dynamic traffic. Finally, we compare the architectures with respect to their normalized cost per terabit per second (Tb/s) and study its sensitivity with respect to the cost ratio of their key components.

Design and Performance Evaluation of Contention Resolution Schemes with QoS Support for Multimedia Traffic in High Bit-Rate Wireless Communications

This paper considers the problem of contention resolution algorithm for multi-class with quality of service (QoS) constrained for wireless communication. Five different channel reservation schemes are proposed, namely, UNI+MLA, UNI+DS, UNI+DS+MLA, Partial UNI and Partial UNI+MLA schemes for multimedia traffic, all are extensions of our recently proposed UNI scheme for single-class traffic. The goal is to achieve the highest system performance and enable each traffic type to meet its QoS requirements. We evaluate the performance of each scheme by mathematical analysis. The numerical results show that our proposed schemes are effective in enabling each traffic type to achieve the best successful rate possible in this kind of environment. Finally when comparing between our proposed schemes and conventional technique in terms of both throughput performance and QoS requirements it is found that the UNI+MLA, UNI+DS+MLA and Partial UNI+MLA schemes are relatively efficient and suitable for practical applications.

Demonstration of Deflection Routing With Layer-2 Evaluation at 40 Gb/s in a Three-Node Optical Burst Switching Testbed

We developed an optical burst switching (OBS) network testbed with three nodes, where each node consisted of a fast 5 5 (Pb,La)(Zr,Ti)O optical matrix switch. A newly developed Ether frame media converter was successfully used to evaluate Layer-2 performance of the testbed, with a line rate of 40Gb/s. A dynamic deflection routing scheme for contention resolution is implemented. Error-free switching with 40-Gb/s payload was achieved over the three nodes, promising low frame loss due to dynamic operation. By comparing effects of random collision with and without deflection routing for varying loads, we demonstrate that near-theoretical low frame loss is achievable in fast Layer-2 (Ether frame) transport over OBS networks.

Reflection-Based Deflection Routing in OPS Networks

An important issue in the realization of optical packetswitched (OPS) networks is the resolution of packet contention caused by the lack of RAM-like optical buffering. Although an optical buffer using fiber delay lines (FDLs) has been proposed, its capacity is extremely limited. There have been several studies of this problem. One approach is deflection routing, which is widely used in electronic packet-switched networks or optical burst-switched (OBS) networks. However, in OPS networks, packet lengths are short, so that the speed requirement for route lookup is very stringent. If the network topology is geometric, such as a Manhattan Street Network (MSN), hop-by-hop routing can be implemented by simple optical logic devices without an electronic routing table. However, if the topology is not geometric, it is hard to implement deflection routing electronically or optically. Another approach is reflection routing, which is easy to implement but has a higher probability of packet loss than does deflection routing. In this paper, we propose a packet contention resolution scheme, reflection-based deflection routing, which is based on reflection routing and enables switching the reflected packet to an alternate path if its primary path remains congested. Our method alleviates the time limitation on setting an alternate path by making use of the packet reflection latency and also reduces the probability of packet loss. We evaluate the performance of the proposed method by simulation experiments and show its effectiveness.

Contention avoidance and resolution schemes in bufferless all-optical packet-switched networks: a survey

Optical Packet Switching (OPS) is the promising switching technique to utilize the huge bandwidth offered by all-optical networks using the DWDM (Dense Wavelength Division Multiplexing) technology. However, optical packet contention is the major problem in an OPS network. Resolution and avoidance are two schemes to deal with the contention problem. A resolution scheme resolves collisions, while an avoidance scheme tries to reduce the number of potential collision events. Many OPS architectures rely on optical buffers to resolve contention. Unfortunately, optical buffering technology is still immature as it relies on bulky optical fiber delay lines. Furthermore, it requires a complex control. Therefore, a bufferless OPS network could still be the most straightforward implementation in the near future. In this article, we survey the contention resolution and avoidance schemes proposed for bufferless OPS networks. We also review the resolution and avoidance schemes that can handle the Quality of Service (QoS) issue in a QoS-capable bufferless OPS network.

光突发高速网络集成方案的性能分析

A new integrated scheme based on resource-reservation and adaptive network flow routing to alleviate contention in optical burst switching networks is proposed. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time to avoid the packet out-of-sequence arrival problem. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution schemes based on conventional routing. Through extensive simulations, it is shown that the proposed scheme not only provides significantly better burst loss performance than the basic equal proportion and hop-length based traffic routing algorithms, but also is void of any packet re-orderings.

A k-Round Elimination Contention Scheme for WLANs

The contention resolution scheme is a key component in carrier sense based wireless MAC protocols. It has a major impact on MAC’s performance metrics such as throughput, delay, and jitter. The IEEE 802.11 DCF adopts a simple contention resolution scheme, namely Binary Exponential Backoff (BEB) scheme. The BEB achieves a reasonable performance for transmitting best-effort packets in small-size wireless networks. However, as the network size increases, it suffers from inefficiency because of the medium contention, which leads to reduced performance. The main reason is that the BEB mechanism incurs an everincreasing collision rate as the number of contending nodes increases. We devise a novel contention resolution scheme, a k-round elimination contention (k-EC) scheme. The k-EC scheme exhibits high efficiency and robustness during the collision resolution. More importantly, it is insensitive to the number of contending nodes. This feature makes it feasible for use in networks of different sizes. Simulation results show that the k-EC scheme offers a powerful remedy to medium contention resolution. It significantly outperforms the IEEE 802.11 DCF scheme in all the MAC’s performance metrics, and also exhibits better fairness.

Partial predeflection—a novel contention resolution scheme for optical burst switching networks

A novel contention resolution scheme for optical burst switching (OBS) networks is proposed. Traffic payload is classified into two types at the edge nodes, and they are transferred through the core nodes using two different routing algorithms—least-hop first routing and shortest-path first routing, respectively, leading to balanced traffic loads among fiber links. By using this contention resolution scheme, active avoidance of burst contention is achieved. Performance evaluation and simulation results indicate that the new scheme outperforms the commonly used shortest-path first routing and is robust under both Poisson and self-similar traffic. Furthermore, the new scheme can provide quality-of-service (QOS) differentiation when used with wavelength conversion, and the implementation of this scheme is easy, which makes OBS technology more applicable in network engineering.

On-the-Fly All-Optical Contention Resolution for NRZ and RZ Data Formats Using Packet Envelope Detection and Integrated Optical Switches

We present a packet-by-packet contention resolution scheme that combines packet detection, optical space switching, and wavelength conversion performed in the optical domain by integrated optical switches. The packet detection circuit provides the control signals required to deflect and wavelength-convert the contending packets so that all the packets are forwarded to the same output without any collision or packet droppings. We demonstrate the compatibility of the scheme with both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats by recording error-free operation for 10-Gb/s NRZ and 40-Gb/s RZ packet-mode traffic

System-on-chip communication architecture: dynamic parallel fraction control bus design and test methodologies

Modern system-on-chip (SOC) designs consist of numerous heterogeneous components (embedded CPUs, dedicated hardware, FPGAs, embedded memories and so on) integrated onto a single chip. The on-chip communication is becoming the bottleneck for these SOC designs, and efficient contention resolution schemes for managing simultaneous access requests to the communication resources are required to prevent system performance degradation. A new SOC on-chip communication architecture, Dynamic Parallel Fraction Control Bus, which offers an attractive solution for the problem and addresses shortcomings of existing communication architectures is presented. To demonstrate the benefits of the proposed architecture, several existing communication architectures were compared with the proposed architecture on the basis of two application prototypes. Through experimentation it has been shown that the proposed architecture not only exhibits both hardware simplicity and system performance improvements, but also produces better bus bandwidth control and scalability properties compared with the existing communication architectures.

Analytical Model for Contention Resolution in Synchronous Optical Packet Switching

In optical packet switching, contention is a major source of packet loss. Contention resolution is necessary in order to handle the case where more than one packet tries to leave the switch from the same output link at the same time. This paper presents a contention resolution scheme based on shared output fiber delay lines in a synchronous optical packet. The switch is modeled using a Markov chain. The simulations results agree with the analytical model.

Combining contention resolution schemes in WDM optical packet switches with multifiber interfaces

Feature Issue on Photonics in Switching Optical packet switch (OPS) architectures with multifiber interfaces are considered here to combine space, wavelength, and time domain contention resolution. The switch is equipped with fiber delay lines as well as a pool of tunable wavelength converters that can be shared within the node or the single interface. Contention resolution algorithms can exploit space, wavelength, and time domains. In particular, the proposed multifiber solution, consisting of a bundle of fibers for each interface, allows isolating output wavelengths on each fiber and repeating them on different fibers. As a consequence, the wavelength converters employed become easier to implement due to the narrower bandwidth required for each of them. These architectures also allow implementing quality-of-service mechanisms to obtain an application related performance. Packet loss evaluation is obtained via simulation and analysis in the special case of bufferless design. The advantages of the proposed solution in terms of both performance and cost saving are shown.

Packet contention resolution in slotted optical packet switch using ant-colony based algorithm

An ant-based contention resolution scheme for the slotted optical packet switched networks has been proposed, and the optimal number of fibre delay lines (FDLs) used in the switch under various traffic loads is investigated. The proposed algorithm can makes FDLs and output port assignment so as to improve the cell-loss rate under various traffic loads. It is found for traffic loads 0.9, 0.6, 0.3, the optimum value for FDL is 64 128 and 128.

Performance Analysis of the Contention Resolution Scheme in IEEE 802.16

At present, the mandatory contention resolution that shall be supported by IEEE 802.16 is based on truncated binary exponential backoff algorithm. In this paper, the differences of contention mechanism between IEEE 802.16 and IEEE 802.11 are analyzed. The calculations of performance metrics such as the utilization of transmission opportunity u, the delay of bandwidth request d and the drop probability of bandwidth request pd are presented. Based on simulation results, the effects of contention parameters such as the initial window W, the number of subscriber station n and the number of transmission opportunity Nto are discussed. Some policies to adjust the parameters are also provided. These policies are useful for BS to schedule its uplink bandwidth resource.

Design of All-Optical Contention Detection and Resolution for 40-Gb/s Label-Switched Routers

We present a new scheme for all-optical contention detection and time-domain contention resolution of optical packets in label-switched routers that employ all-optical label recognition. The contention detection subsystem provides all the necessary control signals required to drive an optically controlled buffer which employs 1 times 2 optical switching elements and an optical fiber delay line. The state of the buffer is dynamically controlled on a per-packet basis with all the decisions and processing performed in the optical domain. Physical layer simulations show successful buffering and forwarding of 40-Gb/s optical packets with 2-dB power penalty

A flexible contention resolution scheme for QoS provisioning in optical burst switching networks

Contention resolution is a major issue in bufferless optical burst switching (OBS) networks. The existing contention resolution schemes consider priority and arrival time to resolve contention. For most multimedia applications priority and delay are key parameters for QoS provisioning. In this paper, we propose a new signaling protocol for reducing contention in OBS networks and consider three parameters, namely, priority of the burst, number of hops traversed, and burst size into account to resolve contention. The source node in the proposed protocol can be informed of the contention up to halfway along the path of the burst, and thus, can reschedule the burst accordingly. The scheme is adaptable to both prioritized and delay constrained traffic. We call the scheme OBS- Flex. For selecting a data channel, we propose three channel selection algorithms, namely, Least Recently Used (LRU), First Fit (FF), and Priority Set (PS). We simulate OBS- Flex and compare with preemptive priority just-enough-time (PPJET) contention resolution scheme. We show that OBS- Flex outperforms PPJET in terms of burst loss rates. For simulation, we have considered Poisson and bursty traffic models.

Ant-based contention resolution in slotted WDM optical packet switched networks

This paper proposed an Ant-based contention resolution scheme for the slotted optical packets switched (OPS) networks. The proposed contention resolution schemes are shown to be effective to resolve packet contention and to achieve good performance by using minimum number of fiber delay lines (FDL). Moreover, the cell loss rate is improved by 10% to 40% under various traffic loads using the proposed scheme.

A Novel Contention Resolution Scheme for Optical Burst Switching Network

Optical burst switching (OBS) is a promised newly technology to implemented the all-optical transmission for Internet protocol (IP) traffic. How to effectively resolve the burst contention at the core router and propose a QoS (Quality of Service) supported burst assembly technique is a critical issue in nowadays. In this paper, a novel burst contention resolution scheme for OBS network has been proposed, this scheme based on two main aspects. Firstly, we propose a new burst segmentation approach named both-direction-segmentation (BDS), which could subtly take the advantages of burst head-segmentation and burst tail-segmentation approach. Secondly, corresponding to BDS, a novel burst assembly technique, which we called hybrid burst assembly (HBA) also has been proposed. Different from several existing burst assembly techniques, which only protect high-priority bursts. HBA has also been considered to protect the relatively high-class packets in low-priority bursts. A simulation is given out at the end of this paper, we observe that the proposed contention resolution scheme not only could minimize the losing of packets remarkably but also could efficiently and veritably support QoS for OBS network. The results have some valuable theoretic significances to design the real network in practice.