Ben-Jye Chang

Analysis of adaptive cost functions for dynamic update policies for QoS routing in hierarchical networks

QoS routing for hierarchical networks are adopted for achieving high scalability and efficiency, e.g., the Inter/Intra Internet and the ATM Private Network-to-Network Interface (PNNI) specification. In hierarchical routing, several nodes of lower level are aggregated as a logical node of the corresponding next higher level recursively. Moreover, in PNNI, each (logical) node bundles its state information in the structure of PNNI Topology StateElements (PTSE) and sends to its neighbors periodically. That results in hierarchical routing with inaccurate information. Since, aggregated routing information is exchanged based on a time-based update policy in PNNI. However, the dynamic nature of network status makes it very difficult to set an appropriate update interval. Therefore, in this paper, we propose two cost-based adaptive update policies: Dynamic Cost-based Update policy and Dynamic Cost-based Update policy with hysteresis, which update routing information only when the change of the cost of a link exceeds a threshold. Our numerical results show that the cost-based update policies not only reduce connection blocking probability, but also decrease the frequency of routing information updates. In this paper, we analyze three approaches to define link cost function and examine the performance of the cost-based update policies under these link cost functions. We find that the proposed cost-based adaptive update policies together with the Markov Decision Process-based link cost function yield the best performance.

Performance analysis for hierarchical multirate loss networks

The reduced load approximation technique has been extensively applied to flat networks, but the feasibility of applying it to hierarchical network model has seldom been described. Hierarchical routing is essential for large networks such as the Internet inter/intra-domain routing hierarchy and the Private Network to Node Interface (PNNI) standard. Therefore, this paper proposes an efficient and accurate analytical model for evaluating the performance of hierarchical networks with multiple classes of traffic. A performance analysis model with considering multiple classes of traffic, the complexity of analytical and explosion of computation will be extremely increased, and hence, result in inaccurate analytical. The issue of multiple classes of traffic has to be addressed in performance analysis model. In this paper, we first study the reduced load approximation model for loss networks, and then propose a novel performance evaluation model for large networks with multirate hierarchical routing. The hierarchical evaluation model is based on decomposing a hierarchical route into several analytic hierarchical segments. Once the blockings of these hierarchical segments are accurately determined, the blocking of the hierarchical path can be estimated accurately from these segments blocking. Numerical results indicate that the proposed hierarchical reduced load approximation yields quite accurate blocking probabilities as compared to that of simulation results. Furthermore, the accuracy of the proposed hierarchical reduced load approximation heuristic is independent of the blocking or the offered traffic load. Finally, we also draw some remarks on the convergence of the reduced load based approximation analysis model.

Efficient hierarchical QoS routing in ATM networks

For reducing network information to achieve scalability in large ATM networks, ATM Private Network-to-Network Interface (PNNI) adopts hierarchical routing. Consequently, although routing complexity is significantly reduced, numerous issues in PNNI routing require further study to achieve more efficient, accurate, scalable, and QoS-aware routing. Several methods are adopted herein to achieve efficient, scalable, and QoS-aware ATM PNNI routing. First, an efficient aggregation scheme, referred to as Asymmetric Simple, is proposed. The aggregated routing information includes available bandwidth, delay and cost. Second, two approaches for defining link costs are investigated, namely, the Markov Decision Process (MDP) approach and the Competitive On-Line (COL) routing approach, and these are compared with the Widest Path (WP) approach. Finally, a dynamic update policy, referred to as the dynamic cost-based update (DCU) policy, is proposed to improve the accuracy of the aggregated information and the performance of hierarchical routing, while decreasing the frequency of re-aggregation and information distribution. Simulation results demonstrate that the proposed Asymmetric Simple aggregation scheme yields very good network utilization while significantly reducing the amount of advertised information. Between these two link cost functions, the MDP approach provides a systematic method of defining call admission function and yields better network utilization than the COL approach. The proposed DCU policy also yields an enhanced network utilization while significantly reducing the frequency of re-aggregation and the amount of distributed aggregation information.

Analyses of Relay Nodes Deployment in 4G Wireless Mobile Multihop Relay Networks

In 4G cellular networks: LTE/LTE-Advanced and the mobile WiMAX network, some key impact factors: white Gaussian noise, wireless interference, shadow fading, etc., degrade signal transmission quality and reduce wireless service coverage significantly. The degradations can be improved by deploying more eNBs or BSs, but the expensive eNB/BS extremely increases network cost. The specifications of LTE-Advanced and IEEE 802.16j thus propose a relay-based scheme, namely mobile multihop relay (MMR) networks, to cooperate with the existing cellular network while not obviously increasing the relay station (RS) deployment cost. Various types of RSs: Fixed RS, Nomadic RS and Mobile RS, can be adopted in MMR networks. To efficiently deploy different types of RSs becomes a critical issue. Thus, this paper first analyzes the impact factors: transmission quality, deployment price, service coverage and RS overlap index, and then models the cost-effective issue of the RS deployment as an optimization problem. The paper proposes an adaptive cost-based RS deployment (ACRD) approach to form a cost function in terms of all impact factors, and then solves the optimization problem by determining the RS deployment with the least network cost as the solution. Numerical results demonstrate that ACRD outperforms the compared approaches in network cost, transmission quality, RS deployment price, service coverage, and RS overlap index. Additionally, ACRD deploys more RSs on the areas with high-density populations and thus increases transmission quality and guarantees the quality of service (QoS). Finally, the worst case running time of ACRD is analyzed, which requires

On the reliability and utilization enhancement for local repair in on demand ad hoc networks

T(n) = O(I \cdot P)

Cross-layer Based Delay-constraint Adaptive Polling for High Density Subscribers in IEEE 802.16 WiMAX Networks

T(n)=O(I·P).

Distributed route repair for increasing reliability and reducing control overhead for multicasting in wireless MANET

The IEEE 802.16 standard adopts a centralized resource-allocation mechanism to poll nodes with three polling modes, i.e., the unicast, multicast, and broadcast polling modes, depending on the residual bandwidth of the base station (BS). In the multicast and broadcast polling modes, the BS uses the truncated binary exponential backoff (TBEB) algorithm as the contention-resolution process (CRP) for mobile nodes to access the wireless network while the traffic load increases up to saturation. The random contention-based TBEB used in the initial ranging and bandwidth request suffers from high collision probability under a high traffic load. TBEB thus significantly degrades the grade of service (GoS), particularly while performing handoff in the mobile (IEEE 802.16e) or multihop relay WiMAX (IEEE 802.16j) networks. Additionally, WiMAXs TBEB exhibits two critical problems. First, TBEB neglects the node priority (i.e., the new or handoff node) and the service flow class (i.e., the real-time or nonreal-time service class); thus, it cannot achieve the optimal network revenue. Second, all different-priority connections immediately transit to the same minimum contention windows (CWs) after winning contentions and then easily lead to high collision probability at succeeding contentions. Therefore, this paper first proposes an efficient contention-resolution algorithm that consists of three key contributions: 1) providing the adaptive minimum-maximum backoff-value algorithm (AM^2) to partition collision domains; 2) supporting a dynamic waiting-penalty algorithm (DWP) for successful contentions; and 3) differentiating the decrements of CWs (DDW) to avoid collisions, even though the contentions randomly choose the same CW value. Second, we model the proposed approach as a discrete-time Markov chain model and then mathematically analyze several important metrics, i.e., the collision probability, access delay, GoS, and throughput. Numerical results indicate that the analytical results are very close to the simulation results, which justify the accuracy of the analytical model. Additionally, the proposed approach outperforms IEEE 802.16 and all compared approaches in collision probability, delay, GoS, and network throughput.

Modeling and analyzing the performance of adaptive hierarchical networks

The ad hoc on-demand distance vector (AODV) routing protocol is proposed for achieving dynamic, self-organizing and on-demand multihop routing among mobile nodes in mobile ad hoc networks (MANETs). In AODV, wireless links may be lost occasionally due to the nodes on the routing path that are unreachable. For solving the problem, the AODV protocol provides a local repair mechanism that tries to find an alternative route to destination by broadcasting the RREQ message from the upstream node of the broken. Although the local repair mechanism works with a specified TTL to limit the repair range of RREQ, large number of the broadcast RREQ messages result in extensive control messages and obvious power consumption for transmitting these broadcast messages. Therefore, in this paper we propose an unicast-type multihop local repair protocol to recovery the lost links efficiently while increasing network reliability, increasing utilization, minimizing the number of control messages and shortening the repair delay. Meanwhile, the optimal number of hops of neighbor table is also analyzed. Numerical results indicate that the proposed multihop local repair approach outperforms other repair approaches in fixed successful rate, control message overhead and network utilization