All‐Optical WDM Cross‐Connect Meshed‐Ring Communications Networks

We study the survivability of a meshed-ring communication network that employs cross-connect switches. For WDM networks, the cross-connect switches are implemented as wavelength routers. Nodes can also provide cross-connection at the ATM VP (virtual path) level. By meshing the ring, the nodal degree of connectivity is increased as compared to a ring topology, and thus more alternative (protection) paths are available. For routing purposes, wavelength subnetworks are embedded in the topology. Nodes communicate with each other across one of the subnetworks to which both belong. We consider two types of subnetwork topologies to simplify the routing in a normal (nonfailure) situation. For each type of subnetwork, different protection methods are proposed to protect against a single link and/or nodal failure. The throughput performance of such meshed-ring networks under failure conditions is clearly superior to that achieved by (SONET) ring networks. We show that certain protection methods even result in lower values of the protection capacity as well as the protection capacity ratio (i.e., the overall capacity used under a failure divided by the total capacity) as compared to ring networks. We also present methods for constructing wavelength subnetworks to achieve single-failure protection using the minimal number of wavelengths.

Since routers in IP network are connected with ATM virtual path (VP) permanent virtual connection (PVC) and each VP contains bundles of VCs, a VP layer network can serve as a server layer and each IP layer network can be a client layer. Therefore the effective Internet service provisioning completely depends on the reliability of VP server layer network from the perspective of the optimality and the network survivability. This paper proposes the distributed ATM VP PVC restoration framework with the dynamic rerouting schemes in hierarchical transport network. The rerouting algorithm aims to provide rapid ATM VP PVC restoration in the case of fault or performance degradation in terms of maximization of network resource utilization and satisfaction of the end user's QoS requirement. It guarantees the IP network survivability in spite of ATM network faults or performance degradations. In addition, this paper evaluates the rerouting performance for a real network, the High Speed Information Network (HSIN).

This paper discusses how a backup virtual path (VP) between each pair of a source node and a destination node is set up such that when some nodes and links in primary VP's fail, primary VP's are changed to backup VP's rapidly. Then, this paper proposes a multiagent-based method for such rapid restoration from primary VP's to backup VP's. The proposed method consists of the following three steps. The first step enumerates candidates of backup VP between each pair of a source node and a destination node. In the second step, capacities of shared links in backup VP candidates between different pairs of a source node and a destination node are obtained. The last step determines a backup VP with the minimum capacities of shared links between each pair of a source node and a destination node. The proposed method has potentially good adaptability for change of both network resource such as topology and link capacity and resource requirements such as capacities of primary VP and backup VP.

BFRA: bounded flooding routing algorithm for provisioning the globally optimal route in a hierarchical ATM network

The future Internet will support a large variety of services whose QoS requirements may vary widely. In order to provide scalable quality of service traffic aggregation may be necessary. We examine several approaches to providing scalable QoS services which includes soft QoS with relative performance guarantees, and hard performance guarantees signaled by RSVP over an aggregated cell switched core. In these approaches QoS is based on aggregate traffic. The question then arises as to what level of QoS is perceived by individual flows within the aggregate. This has an important implication on QoS guarantees which the network can make to individual users. To provide answers to the above question we analyse per-flow and aggregate QoS in an ATM virtual path (VP) which is used as an example of a cut-through handling IP flows. Using cell loss as a measure of QoS, our analysis allows us to investigate the impact of the parameters of individual flows on per-flow QoS. We then compare per-flow QoS against the QoS experienced by the aggregate flow in the VP. Based on numerical tests we find that cell loss experienced by individual flows may be very different from cell loss experienced by the aggregate flow. Thus if aggregate cell loss is used as a QoS constraint in dimensioning of VP this may lead to unfair treatment of flows and hence to potential user dissatisfaction.

Communication performance comparisons, in terms of message latency, between mesh and hierarchical ring interconnection networks for shared-memory multiprocessors are developed. Traffic in the networks is assumed to consist of the short, fixed-length messages needed for remote-memory read/write operations and cache coherency control. Square-mesh networks with bidirectional links and no end-around connections are compared to two- and three-level hierarchical rings. Wormhole routing is used in the meshes, with messages consisting of / flits, with each flit containing b bits. In the ring networks, each ring segment can contain a complete message of f × b bits. Meshes and three-level rings provide comparable delays for system sizes of up to 200 or 300 processor clusters. The delay comparisons are valid only for the lightly loaded traffic case in which contention and blocking are low. This is the situation in practical shared-memory multiprocessor systems with a low cache miss rate and a high physical locality of reference in the global address space.

A quantitative comparison of pure ring and pure mesh survivable network alternatives in a metropolitan study network is provided. The results lead to the development of B-DCS technology to convert the capacity efficiency of mesh restoration methods into economic advantages. An architecture for cooperative interworking between ADM and DCS nodes to realize a survivable access and transport network is introduced. The concept of a survivable arc (as opposed to a pure ring) for cooperative interworking between ADM-based ring and DCS-based mesh restoration technologies is illustrated. >

This paper presents two distributed end-to-end shared restoration algorithms in a multi-domain network environment. While the first proposed algorithm yields a pair of ldquolink-disjointedrdquo paths between any given pair of nodes in the network, the second algorithm computes a pair of ldquodomain-disjointedrdquo paths. To address the problem of limited information exchange among the domains, the multi-domain network is topologically aggregated as a single-domain network, called virtual path network, in which each domain is abstracted by its border nodes interconnected by point-to-point virtual paths. The performance of both algorithms are evaluated and compared through simulation experiments.

A ring architecture that uses the asynchronous transfer mode (ATM) virtual path (VP) concept to reduce the SONET ring cost in terms of bandwidth management is discussed. The add-drop multiplexer (ADM) proposed for VP ring architectures can evolve from existing SONET ADMs by replacing the STS-3 termination cards by the ATM STS-3c line cards. Existing standard self-healing schemes and protocol SONET rings can be applied to proposed ATM/SONET VP rings. A case study based on a BCC (Bellcore client company) ring network and the sensitivity analysis suggests that the proposed ATM VP ring architecture may be a cost-effective option for implementing the distributed ring grooming system at the DS 1 level. The proposed VP self-healing rings are not only used to carry existing DS 1 and DS 3 service, but can also be used to more cost-effectively consolidate switches for public-switched services and for SMDS, frame relay, and FDDI in metropolitan areas.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mesh networks, motivated by wireless neighborhood networks are composed of static wireless nodes that have ample energy supply. Each of these wireless nodes can be equipped with multiple radios, called a multiradio/multichannel node, and each of the radios can be configured to a different channel to enhance network capacity. All wireless nodes cooperatively route each otherpsilas traffic to the Internet through one or more Internet Transit Access Points (TAPS), which are gateways to the Internet. Nodes may also communicate with each other directly through the mesh network without going through TAPS. Supporting communication among mesh nodes and TAPS requires the use of routing protocols that must be combined with a routing metric to determine which route among all possible routes between a pair of nodes will be used. The design of effective routing metrics, however, depends on the specific characteristics of the target network. For example, the severe energy constraints of sensor networks demand the design of energy efficient routing, while the mobility of nodes in ad hoc networks demand the design of protocols that can efficiently maintain connectivity. The unique combination of static nodes with the shared nature of the wireless medium in mesh networks also imposes specific requirements for the design of routing metrics. In this paper it was analyzed the proposed IPRA (Intelligent Portal Routing Algorithm) protocol and its performances in comparison with those offered by the AODV (Ad-hoc on Demand Vector) and DSDV (Destination Sequence Distance Vector) protocols.

In WDM networks, the bandwidth request of a traffic stream is usually much lower than the capacity of a wavelength. Traffic grooming can aggregate low-rate connections onto high-capacity lightpaths to make efficient use of the bandwidth. But most of the researches related to traffic grooming focused on ring networks, and fewer concerns are about the dependable traffic grooming of low-rate connections in WDM mesh networks. In our study, we present a Hamiltonian Cycle Protection based Traffic Grooming algorithm (HCPTG) considering both the survivability and traffic grooming in WDM mesh networks. Simulation results show that good performance can be achieved in terms of capacity efficiency.

Adaptive, in-call, bandwidth reservation may be used to enhance bandwidth utilization in a policed ATM virtual path shared by traffic streams originated by many bursty sources. The mechanism is found to be effective when large changes in the aggregate traffic rate are slow in comparison to the feedback delay with which a requested change in the reserved rate is obtained. We present a model, based on Markov-modulated sources and stochastic fluid methods, for performance analysis of the proposed mechanism. The model, corroborated by simulations, is used to study the effects of feedback delay. >

The paradigm of wireless mesh networks has matured in the last decade after extensive research and development. As opposed to the time of their inception, current mesh networks are expected to deliver carrier-grade access services to their users. With the increasing expectations, it is generally recognized that there is a lack of understanding of the level of service continuity that mesh networks can provide to its users. In this research, we address a set of network design problems and propose solutions to improve the service continuity of wireless mesh networks. First, we investigate power control as a network layer problem in mesh networks. It is commonly acknowledged that reducing transmit power levels of nodes to the minimum required to retain connectivity always increases network capacity. In this work, we show that increasing power level of nodes can be beneficial in many cases depending on network’s traffic and topological characteristics. With extensive analysis and simulations, we characterize achievable spatial reuse and capacity with respect to power control in various practical scenarios. Second, we address the problem of generation of traffic hot-spots in wireless networks, and propose a novel power control scheme for load balancing. Using a heuristic based on the concept of centrality, we show that if we increase the power levels of only the nodes which are expected to relay more packets, significant relay load balancing can be achieved even using shortest path routing. Different from divergent routing schemes, such load balancing strategy is applicable to any arbitrary topology and traffic pattern. With this understanding of power control and load balancing, we investigate the service continuity issues of an urban-scale mesh networks. We define and study two essential service continuity metrics - connection robustness (K-center availability) and performance robustness (K-center performability). K-center availability is the fraction of the time a mesh network is available to its users, while performability is a composite measure of performance (here - throughput) and robustness that captures aggregate experience of mesh users over a long period of time. We develop efficient algorithms for estimating these quantities for large urban-scale meshes and study their characteristics in various existing mesh networks. Our study reveals numerous novel insights that can help in designing mesh networks with high availability and performability. While evaluating the performability, we used ideal case throughput performance estimation that ensures fair network resource allocation among the flows. Although this allows faster computation which is especially necessary for large state space exploration, it is difficult to implement in real-world using CSMA/CA MAC. To address this, we target the issue of unfair and lower utilization of network resources in wireless networks. Specifically, in a mesh network, nodes closer to gateways often achieve a larger share of bandwidth resources while nodes farther away often starve for useful bandwidth. Using back-pressure utility maximization framework, we provide a solution to the issue of spatial bias that can be implemented using current 802.11 standards. To further increase the efficiency of back-pressure policy in mesh networks, we propose a dynamic packet aggregation scheme that is especially effective in Internet-like packet size distribution. Along the same lines, we use the back-pressure invariants to develop a variable channel width assignment scheme that can yield maximum benefits of using varying-sized channels while remaining fair in network-wide resource allocation.

Inter-Cell Interference (ICI) is always a key problem in Fractional Frequency Reuse (FFR) system to be focused on, which should be well resolved to pursue higher throughput and better power efficiency. In this paper, we investigate throughput and power efficiency of RR scheduling in FFR system by both closed-form expression and Monte Carlo trials method. We improve a previous throughput model by applying variable subcarrier distribution scheme and upgrading expression for the Cumulative Distribution Function (CDF) of SINR. Then we propose a new closed-form expression of average cell throughput. The fairness performance of this model is better than that using fixed subcarrier distribution scheme. Meanwhile, an optimal radius threshold is selected so as to achieve best throughput performance. Then we manage to explore the relationship between cell power efficiency and transmit power based on the optimal radius threshold. From both analytical and simulation results, it is shown that power efficiency is monotonically decreasing with transmit power. Hence operational power is introduced into power efficiency as energy consumption for base station. After that, the highest power efficiency can be reached by setting a proper and reasonable transmit power.

Opportunistic spectrum access and adaptive power management are effective techniques to improve throughput, delay performance, and energy efficiency for wireless networks. In this paper, we consider the joint design of opportunistic spectrum access and adaptive power management under the setting of multi-radio nodes and multi-channel wireless local area networks (WLANs) under the distributed coordination function (DCF) mode. This design problem is particularly challenging due to the conflicting nature of the multi-radio capability of a node, i.e., multiple radios improve throughput and delay performance at the cost of increased energy consumption. To address this problem, we propose a power-saving multi-channel MAC protocol (PSM-MMAC), which is capable of reducing the collision probability and the waiting time in the ‘awake’ state of a node, resulting in improved throughput, delay performance, and energy efficiency. The key ideas of PSM-MMAC are the following: we first estimate the number of active links; given this estimation as well as queue lengths and channel conditions, we appropriately select channels, radios, and power states (i.e., awake or doze state); then we optimize the medium access probability in p-persistent CSMA used in the data exchange. Another contribution of this paper is an analytical model that characterizes the throughput performance. Simulation results validate the accuracy of our analytical model and show that our proposed protocol is able to significantly improve both throughput and energy efficiency.