Ho-Ting Wu

The design of QoS provisioning mechanisms for wireless networks

Two mechanisms are proposed in this paper to be incorporated with IEEE 802.11e EDCA MAC protocol for providing the QoS provisioning capability of such network. First, the call admission control function, which considers the inherent contention access feature of 802.11 MAC, aims to satisfy the QoS requirement of established higher priority connections, while protecting the minimum reserved bandwidth of traffic flows with lower priority at the same time. In addition, the proposed adaptive contention window adjustment mechanism dynamically adjusts the maximum and minimum contention window size based upon the equivalent established connection number observed by each individual access category. Such approach reduces the channel contention probability and packet access delay effectively. Performance results via simulations have shown the advantages achieved by employing these two mechanisms.

Mobile awareness based cluster selection mechanisms in wireless ad hoc networks

We propose an efficient clustering scheme for a wireless ad hoc network, based on the moving characteristics of the mobile nodes. The instantaneous mobility behavior for a node equipped with a mobility measuring tool, such as GPS, is readily available. However, for a mobile node without such tool or one in an environment where the measuring tool cannot function properly, we develop a simple heuristic mechanism to derive the mobility index, used for characterizing its instantaneous nodal mobility. The developed mobility estimation algorithm is fully distributed and self organized. Performance results via simulations reveal that the estimated mobility index of a node follows a linear relation with its own real speed in various networking environments. Next, we apply the obtained mobility index to derive the mobile awareness based cluster selection scheme. In general, we choose the currently slowest moving node as the primary candidate for the clusterhead. Compared with other well known clustering schemes, performance results have demonstrated that our mechanism can achieve a more efficient and stable clustering architecture for different networking topologies.

A switched delay line based optical switch architecture with a bypass line

This paper proposes a new switching architecture to be used in all-optical networks. The proposed switch, M-B-Quadro switch, is extended from an original 2/spl times/2 two-stage multi-buffer switched delay line based optical switching node, known as M-Quadro node. By incorporating bypass lines and employing a novel switch control strategy, denoted as LAVS, the switching node can effectively resolve packet contentions, thus reducing the packet deflection probability substantially.

A Novel Mobility Model of Diverse Average Speed and Uniform Node Distribution in Mobile Ad Hoc Networks

Most wireless protocols and algorithms proposed in mobile ad hoc networks (MANET) are evaluated and compared by using simulations. The impacts of various simulation parameters are noticeable. However, the effects of the mobility model do not attract many attentions until recently. The random waypoint (RWP) mobility model, due to its simplicity, is one of the most often deployed mobility models in simulations. But it implicitly introduces many defects such as average speed decaying and un-uniform node distribution. In this paper, we propose a novel mobility model, general ripple mobility model (GRMM), to reduce the above mentioned problems in RWP. Furthermore, GRMM can provide another great feature, diverse average speed (DAS), to generate different average speed mobility patterns easily within the same speed range. Simulation results have shown that GRMM can simultaneously achieve uniform node distribution and diverse average speed

Performance analysis for hierarchical resource allocation in multiplexed mobile packet data networks

The general packet radio service (GPRS) can be thought of as an overlay network above a Global Systems for Mobile (GSM) network. In cooperation with the GSM system, GPRS supports both voice and packet data services. Obviously, combining voice and data traffic implies the nature of contending with finite radio resources. The paper focuses on voice/data integrated GPRS downlink traffic and proposes two hierarchical resource allocation strategies by considering time slots and radio blocks simultaneously with two different TDMA frame configurations. The radio block based resource allocation can characterize the multiplexing scheme of the practical GPRS operation. The performance of the proposed strategies were evaluated analytically by multidimensional Markov chain and verified through intensive computer simulations. Based on both the analytical and simulation results, it showed that the proposed allocation strategies can offer high utilization of transmission resource, as well as low blocking probability to GPRS users. The results of the study provide not only a practical thinking for implementation but also a guideline for analysis.

Self-similar traffic assessment on QoS service classes of WiMAX network

WiMAX features several QoS service classes to schedule different types of traffic. In this paper, we will assess the existence of self-similar traffic for each service class. The experiment starts by capturing the traffic data with a dedicated SNMP-based Network Management System (NMS). NMS manages the deployment of fixed WiMAX network defined in IEEE 802.16d-2004 Standard and records the inbound and outbound traffic for specific object IDs (OIDs). We consider several criteria to generate the traffic for our WiMAX test-bed network such as QoS service class, traffic intensity, and application type. The recorded traffic then will be analyzed using variance plot, and RS-plot. The result shows various degree of self-similarity for different types of QoS service classes and traffic intensities.

An application layer multi-source multicast with proactive route maintenance

Application layer multicast is an alternative to network layer multicast. The existing application layer multicast approaches are focus on single source multicast and insufficient in supporting distributed applications that require multi-source and fast recovery abilities with dynamic membership. This paper proposes a novel application layer multicast and its proactive recovery approaches for multi-source applications. The member in the proposed approach configures a partial tree structure for each source-specific data delivery tree, and then the cooperative execution of the proposed approach at each member defines an implicit multicast delivery tree for each source node. The implicit delivery tree structure can not only avoid bottleneck and single point-of-failure problems of single share-tree solution suggested in [2], but also simplify the recovery from node departures to table-lookup operations. Extensive simulations demonstrate that our proposal is effective to handle multi-source multicast delivery and reduce recovery time caused by departed nodes.

General Ripple Mobility Model of Speed-Time Pairing

The research works on the mobile ad hoc networks (MANET) have attracted wide attentions over the past few years. In order to evaluate and verify the underlying protocols or applications, researchers run simulations to generate results. By controlling different simulation parameters, we can run our programs in diverse simulation scenarios. Mobility model of mobile nodes in MANET plays an important role in simulations but its importance is often ignored. Random waypoint (RWP) is one of the most deployed mobility models in papers. RWP has the properties that are understandable and quick to implement. Until recently, several defects in RWP is unknown. One is decaying average speed and another is border effect. Besides the problems in RWP, there is still a missing property in many mobility models. Diverse average speed (DAS) is a more realistic requirement for mobility models. Most mobility models only can generate one average speed scenario with the same speed range. It is reasonable to provide different average speed within the same speed range. We propose general ripple mobility model (GRMM) of speed-time pairing to provide a similar mobility model to RWP without the defects of RWP. GRMM also provides DAS to generate different mobility scenarios. The simulation results show that GRMM of speed-time pairing can generate the mobility pattern of uniform spatial distribution and diverse average speed.

A novel multicast mechanism for optical local area networks

In this paper, we propose a simple and efficient multicast scheduling algorithm, the Lookback Queue Access (LBQA) protocol for the employment in an asynchronous WDM optical star network. Network nodes use ALOHA based random access schemes to send their reservation packets over a common packet reservation control channel. A central traffic scheduler is allocated to coordinate message transmissions. The central scheduler carries out the LBQA scheme in real time in two phases. The first phase is to search (through input queues) for a candidate multicast message that can be sent, without partition, to all of its intended recipients. If phase 1 fails, the second phase is then activated to efficiently partition a multicast message into multiple transmissions. Performance results conducted via simulations have revealed that networks employing such a scheduling mechanism can exhibit superior network throughput levels and delay performances. To obtain sustainable high performances, we further propose an interconnected dual-star structure employed with the enhanced scheduling mechanism, the DS_LBQA algorithm. By using a simple heuristic approach, the DS_LBQA scheme is able to successfully exploit the inter data channels and properly utilize the wavelength reuse property of the intra data channels. Performance results have demonstrated the merits of deploying the DS_LBQA multicast algorithm in such a dual-star structure.

Flexible mobility models towards uniform nodal spatial distribution and adjustable average speed

To evaluate Mobile Ad Hoc Networks (MANET) protocol, we often resort to simulation approaches for evaluating system performances and adjusting design parameters accordingly. The mobility model imposes a profound impact on the performance of MANET mechanisms. The Random Waypoint (RWP) model, due to its intuitive and easy implementation, is the most widely used mobility model in MANET research. However, recent research results have shown that RWP exhibits a few defects. These problems include: the decaying average speed as the simulation time increases, border effect and the difficulty of generating adjustable average speed under the same moving speed limits. In this paper, we propose a new mobility model, called Ripple Mobility Model (RMM) to reduce the aforementioned defects simultaneously, while still maintaining the easy implementation characteristic of RWP. The RMM model is also incorporated with the concept of Lower Speed for Shorter Distance (LSSD) to flexibly generate various simulation scenarios. Performance results via simulations reveal that our proposed mobility model is able to achieve our intended goals. Keywords-Mobile Ad Hoc Network (MANET); Random Waypoint (RWP); Mobility Model; Border Effect; Lower Speed for Shorter Distance (LSSD); Ripple Mobility Model (RMM)