K-terminal reliability in ring networks

The authors present a new formula for computing K-terminal reliability in a communication network whose stations and links (vertices and edges) form a network graph G having a ring topology, where K-terminal reliability is the probability R_K(G) that a subset of R specific terminal stations in G can communicate. This new formula is applied to three Fiber Distributed Data Interface (FDDI) ring-network topologies, and for each topology the authors derive closed-form polynomial expressions of R_K(G) in terms of the failure probabilities of links, network ports, and station common units. The authors define the concept of the K-minimal Eulerian circuit and use combinations of these circuits to obtain K-graphs and their resulting dominations, thus extending the use of K-graphs to ring networks in which data messages, tokens, or other control frames traverse operative network links with an Eulerian tour. Distinct K-graphs having a nonzero sum of dominations are called noncanceled K-graphs and correspond exactly to terms in closed-form polynomial expressions of R_K(G). The authors show that trees have only one K-graph and that counter-rotating dual rings and rings of trees have at most 2K+1 noncanceled R-graphs. These results contribute the first closed-form polynomial R-terminal reliability expressions for the ring-of-trees topology. The results are useful in evaluating dependability, reliability, availability, or survivability of token rings and similar networks     

基于被动测量的网络故障诊断

A new passive method for automatic discovery and location of network failure is proposed. This method employs a passive measurement to collect information and events from network traffic, and employs a model-based reasoning system to detect and locate network faults.Measurement points are deployed in a backbone network to capture the traffic and then evaluate the Quality of Service (QoS) metrics of end-to-end IP conversations. A routing model is also established for the observed network to simulate the attributes and activities of routers and links. This routing model also deduces the routing path for each IP conversation, and thus the QoS metrics of IP conversations are mapped into the metrics of paths. With the information of shared links of overlapping paths and network tomography technique, the QoS metrics of links can also be estimated, and the poorly rated links are picked out as failure points. This method is implemented in a tool named Fault-Man, which is deployed in a campus network. Test results have shown its availability in middle-scale networks.     

A quadratic optimization method for connectivity and coverage control in backbone-based wireless networks

The use of directional wireless communications to form flexible mesh backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional homogeneous wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure backbone network requirements such as coverage and connectivity in a dynamic wireless environment. This paper considers the use of mobility control, as the dynamic reposition of backbone nodes, to provide assured coverage-connectivity in dynamic environments. This paper presents a novel approach to the joint coverage-connectivity optimization problem by formulating it as a quadratic minimization problem. Quadratic cost functions for network coverage and backbone connectivity are defined in terms of the square distance between neighbor nodes, which are related to the actual energy usage of the network system. Our formulation allows the design of self-organized network systems which autonomously achieve energy minimizing configurations driven by local forces exerted on network nodes. The net force on a backbone node is defined as the negative energy gradient at the location of the backbone node. A completely distributed algorithm is presented that allows backbone nodes to adjust their positions based on information about neighbors’ position only. We present initial simulation results that show the effectiveness of our force-based mobility control algorithm to provide network configurations that optimize both network coverage and backbone connectivity in different scenarios. Our algorithm is shown to be adaptive, scalable and self-organized.     

Technology 1991: data communications

Significant developments during 1990 are examined, and future trends are delineated. Two major events were the rapid acceptance by end users of the 10BASE-T standard for Ethernet interconnections using unshielded twisted-pair wiring and the widespread acceptance of the fiber distributed data interface (FDDI) by corporate planners and MIS (management information system) people, as well as government planners, as the way to wire the corporate backbone. 1990 also saw commercialization begin of the FDDI interface by which data is transmitted on an optical-fiber network at 100 Mb/s rates. The development of twisted-pair wiring for Ethernet and FDDI will lead to integration of Ethernet. Token Ring, and FDDI local networks in one concentrator in one wiring closet, while the pace of growth of the LAN market continues to accelerate. The seven layers of the Open Systems Interconnection (OSI) protocol received a big boost last year from the US government, and it is likely to become the routine way of organizing data networks worldwide     

Availability of survivable Valiant load balancing (VLB) networks over optical networks

Valiant load balancing (VLB) network has been proposed as a capacity-efficient solution to handle highly dynamic traffic in future backbone networks. In this paper, we study the availability of VLB networks that are overlaid over an optical infrastructure. The main challenges in such a context arise from the unique routing and protection scheme that goes beyond the definition of conventional connection-level service availability as well as the logical link failure correlation that prohibits the use of traditional analytical methods. We propose a network-level availability model to compute the probability that a VLB network is congestion-free under all traffic patterns. Numerical results show that with a proper truncation level, our calculation on availability can be accelerated significantly by generating tight lower and upper bounds. Our main finding is that physical link sharing in a two-layer setting degrades the network availability drastically by several orders of magnitude due to the full mesh requirement for VLB networks, and may remove the capacity efficiency advantage of VLB networks.     

A 1+1 protection architecture for optical burst switched networks

High-capacity optical backbone networks protect their premium customers' information flows by routing two copies of the customer's data over disjoint paths. This scheme, known as 1+1 protection, provides extremely rapid recovery from network failures. We propose an architecture by which 1+1 protection can be extended to optical burst switched (OBS) networks. This architecture is designed by modifying the diversity routing architecture that was originally proposed for nonoptical packet networks and recently applied to networks employing the generalized multiprotocol label switched (GMPLS) architecture. We extend the architecture developed for just-in-time OBS signaling to support 1+1 protection. We also examine design issues that are raised by a difference in the propagation delays of the two disjoint paths across the OBS network. We show that a sufficiently large difference in the propagation delays can cause performance degradations that may result in an unsatisfactory quality-of-service on the protected connection. We examine the impact of this delay mismatch on restoration performance, probability of burst loss, and jitter. Through analysis and simulations, it is discussed how these negative effects can be eliminated.     

Analysis of an M/G/1/N queue with vacations and its iterativeapplication to FDDI timed-token rings

We present the analysis of an M/G/1/N queueing system with vacations under a dynamic time-limited service policy. This method is used to develop a procedure for performance analysis of a fiber distributed data interface (FDDI) network serving buffer-limited stations under asynchronous service. An efficient iteration procedure is employed to evaluate the limiting state distribution of the embedded Markov chain representing the system state process. Using supplementary variables and sample biasing techniques, we derive the queue size distribution at an arbitrary instant of time as well as the packet blocking probability and the mean packet delay. By exploiting the subtle structure of conditional supplementary variables and the recursive property of the conditional residual delay, the Laplace-Stieltjes transform of the packet delay distribution and a time-domain approximation of the packet delay distribution are obtained. For the analysis of a heterogeneous multi-station FDDI network, an iterative procedure which uses repeatedly the M/G/1/N vacation model described above is presented. This procedure provides for a numerically efficient analysis method by employing constructions of the approximate vacation time distributions. We illustrate the application of our analytical techniques to both symmetric and nonsymmetric FDDI network systems     

An Efficient Link Allocation Algorithm for ATM-Based Personal Communication Networks

The wireless personal communication networks (PCN) will play an important role throughout the 1990s and into the next century. Due to the demand for extending the wireless services to integrated services such as data, voice, images and video, a high-speed backbone network to connect the base stations in the microcells is required. One of the possible solutions is to apply the ATM-based backbone network. In such an ATM-based PCN, the communication path between a pair of mobile terminals might be elongated due to the mobility of terminals. Generally, there are two ways to resolve this problem. The first is to migrate the elongated path to a better one when necessary. The other is to design an appropriate backbone network by considering the mobile environment. Recently, several mechanisms based on the former approach have been proposed. In this paper, the latter approach is considered and the design problem of allocating the backbone links among the ATM switches so that the network performance affected by the terminal mobility is kept as less as possible is investigated. We show that this link allocation problem is NP-hard. A simple and efficient heuristic is also proposed for this problem. Simulation results show that based on the backbone obtained by the heuristic, the average length of each communication path is kept as short as possible even under the mobile environment. As a result, the number of successfully established paths in the network is increased significantly.     

FDDI and beyond-a network for the 1990s

The availability of cheap optical fibre and associated transceivers has encouraged the development of the next generation of computer networks. Most prominent among these is the fibre distributed-date interface (FDDI), which is expected to become a standard. The authors describe the principal advantages of the FDDI (namely its size and transmission rate) and outline the apparently bright future of FDDI networks and their applications     

Following the fiber distributed data interface

The fiber distributed data interface (FDDI) follow-on local area network (FFOL) work was initiated in February 1990 by Task Group X3T9.5 of Accredited Standards Committee (ASC) X3 to establish requirements and formal projects for a next-generation LAN. The background for startup of the FFOL project, including its requirements and current status, are presented. It is shown that the higher performance of FFOL and its ability to handle all FDDI data formats will allow its use as a backbone to existing FDDI installations. FFOL will also be used as a replacement for FDDI and other LANs when its higher performance is required     

A concurrent two-layer restoration scheme for GMPLS WDM networks

Next generation backbone networks will likely consist of IP routers as well as optical cross connects (OXCs) and will deploy an optical control plane protocol. Generalized Multi Protocol Label Switching (GMPLS) has been proposed as the candidate of choice for the control plane. Optical fibers may carry large volumes of traffic and therefore adequate mechanisms must exist to enable the network to automatically recover from failures of fiber. In mission critical networks survivability becomes very important. We investigate the problem of autonomous recovery in such networks. The literature contains work in this area that investigates the problem of multilayer recovery. Such recovery had only been sequential in the sense that the published work recovers first in the optical domain, assuming the availability of redundant resources, and then proceeds to recover packet label switched paths. We report a recovery procedure for recovering packet label switch paths (packet LSPs) and lambda label switch paths (λLSP) concurrently. We have conducted an OPNET-based simulation study that compares the performance of the concurrent scheme with the previously published sequential two-layer recovery scheme. The study shows that the concurrent two-layer recovery scheme performs as much as forty-four percent faster than the sequential two-layer recovery scheme.     

Availability Design of Optical Transport Networks

A design technique for reliable optical transport networks is presented. The network is first dimensioned in order to carry a given set of static protected optical connections, each one routed maximizing its availability. The network can be further optimized by minimizing the number of fibers to be installed, while keeping a control on connection availability, which can remain the same or decrease by a prefixed margin factor. Design and optimization algorithms are provided for networks adopting dedicated and shared path-protection. The optimization approach is heuristic. Results obtained by applying the proposed technique to two case-study networks are shown and discussed. These two case-study experiments are carried out exploiting a realistic model to evaluate terrestrial and submarine optical link availability.     

Low‐cost data communication network for rural telecom network management

The backbone networking infrastructure of rural telecom networks is often costly and is of limited bandwidth. The availability of connectivity such as DSL or leased lines is scarce. In order to keep operational costs low, these rural telecom networks are often kept unmanned and are managed from a centralized network management station (NMS). This often requires a low‐cost, efficient and reliable data communication network (DCN) between the rural telecom equipment and the central NMS. The conventional DCN used for telecom management consists either of leased lines or Internet connectivity. These are often costly and not freely available in rural areas. We have developed a new DCN model, based on dial‐up, which is easily available. Using mathematical models and measurements we show that this DCN meets the QoS requirements of a telecom network at an affordable cost. We have implemented this DCN in corDECT networks. This is in use in India and Tunisia, and is under implementation in other similar countries. Copyright © 2007 John Wiley & Sons, Ltd.     

Multiple-availability-level ATM network architecture

Because of their high flexibility, ATM networks have the potential to achieve two objectives: switch cost reduction and multi-level network availability. For that purpose, this article proposes to use virtual circuit (VC) route self-healing schemes to achieve a multiple-availability-level ATM network. Flexible multi-QoS logical ATM network (Full-Net), a new concept for ATM networks, is now being studied at NTT Laboratories. Full-Net is a very flexible network design strategy for survivable networks that is based on a self-healing VC network. Defining several logical configurations of the VC network allows us to support multiple levels of network availability, simplifies the adaptation to future and unknown service requirements, and significantly reduces overall ATM network cost. Offering different levels of availability not only saves the network's resources, but also allows the network operator to provide its customers with services at the most appropriate cost. We introduce the advantages of VC route restoration for ATM networks, and compare virtual path (VP) level and physical level restoration strategies. We explain Full-Net's concept, propose a VC route self-healing scheme, and show the impact of the logical network configurations on network survivability and resource management     

Extending the IEEE 802.1 MAC Bridge standard to remote bridges

The IEEE 802.1 MAC Bridge specification describes transparent local bridges, called spanning tree bridges, that interconnect 802-type local area networks (LANs). The author discusses experience with adapting the spanning tree algorithm to the remote bridge environment, including the addition of a distributed algorithm for utilizing backbone networks while they are configured as backup paths by the spanning tree. This results in local and remote bridge configurations that automatically detect and recover from all failures/restorals in a deterministic way. Once the support of the same spanning tree algorithm is pervasive, it is also possible to add distributed algorithms that allow spanning tree backup paths to be utilized     

网络抗干扰及其评估方法

网络级抗干扰是一个新问题,它与网络的拓扑结构紧密相关。本文研究了无线网中干扰相关性,计算了理想拓扑的干扰独立路径数目的数目。网络抗干扰性能的另外一个问题是评估方法,本文提出了基于平面几何的评估方法,其中包含了距离和方位两个参数。该评估方法计算简单,物理意义明确,能很好地反应无线网的拓扑抗干扰性能。     

Ring-network with a constrained number of consecutively-bypassedstations

A new technique combines prior graph theoretic and algebraic techniques for obtaining closed-form terminal-pair reliability expressions of ring topology networks. The applicability of this technique is illustrated by obtaining closed-form terminal-pair reliability expressions for dual counter-rotating ring networks that use both self-heal and station-bypass switches in which all components can fail. These expressions appreciably extend the utility of prior work on ring-network reliability by incorporating network configuration limitations caused by optical power loss constraints. The number of consecutively bypassed station failures in an optical fiber ring topology network such as those exemplified by FDDI rings or synchronous optical network (SONET) rings is limited by the optical power loss constraints. The combined graph theoretic and algebraic technique permits the incorporation of known results on the reliability of consecutive k-out-of-n:F systems so that closed-form terminal-pair reliability expressions can be derived. The results are a new approach to network-reliability analysis and appreciably extend known theory to new situations not previously analyzed. In particular, the combined graphical-algebraic analysis tool developed here allows ring-network designers to analyze the reliability of ring-network structures thought previously to be too difficult to analyze with closed-form expressions and to be amenable only to reliability approximation by simulation. We use this technique in our derivation of closed-form expressions for terminal-pair reliability in dual counter-rotating ring networks     

Reliable Multipath Provisioning for High-Capacity Backbone Mesh Networks

We investigate reliable multipath provisioning of traffic in high-capacity backbone mesh networks, e.g., next-generation SONET/SDH networks supporting virtual concatenation (VCAT). VCAT enables a connection to be inversely multiplexed on to multiple paths, a feature that may lead to significantly improved performance over conventional single-path provisioning. Other mesh networks such as those employing optical wavelength-division multiplexing (WDM) and multiprotocol label switching (MPLS) can also benefit from this multipath provisioning approach. We propose effective multipath bandwidth as the metric to provision a connection while satisfying its reliability requirements (measured in terms of availability). We demonstrate that effective multipath bandwidth provides more flexibility and lower blocking probability without the cost and the complexity associated with traditional protection schemes developed for optical WDM and MPLS networks. We also investigate the practical problem of provisioning effective multipath bandwidth with cost constraints. We analyze the tractability of the problem and present a heuristic which results in significantly reduced number of blocked connections due to cost constraints.     

Providing quality-of-protection classes through control-message scheduling in DWDM mesh networks with capacity sharing

This paper considers the problem of providing quality-of-protection (QoP) classes and improving the failure-recovery time performance in dense wavelength-division-multiplexing (DWDM) networks that use mesh-based path restoration schemes with capacity sharing. We focus on the signaling process required for reconfiguring the nodes along the preplanned restoration paths, and propose a novel approach for reducing the restoration time and meeting the QoP requirements by coordinating the setup procedures for the backup paths through scheduling. We present priority-based online scheduling algorithms that are amenable to distributed implementation for the problems of: 1) minimizing the worst case restoration time and 2) maximizing the number of connections that meet their QoP-class-specific restoration time deadlines. We also present mixed-integer-linear-program (MILP) formulations for both problems for comparison purposes. The online scheduling methods that we propose use simple connection and/or class-specific information and can be easily implemented with minor modifications to the currently proposed signaling protocols. We apply these methods to signaling protocols that require cross-connect configurations at different nodes to be done in sequence as in the current generalized multiprotocol label switching specification, as well as signaling protocols that allow cross-connect configurations to be done in parallel. It is shown that in both cases, significant performance improvements are achievable through scheduling in terms of both the QoP grades that can be supported and the restoration times, with both the MILP solutions and the heuristics. The improvement in restoration time and restorability through our heuristics can be quite high (e.g., increase from a network restorability performance of 40% to a network restorability of 88%, and a 12% reduction in worst case restoration time).     

FDDI: current issues and future plans

Fiber Distributed Data Interface (FDDI), a set of standards developed by the American National Standards Institute (ANSI) X3T9.5 Task Group, is reviewed. The timed token access method, used to share the medium among stations in this 100-Mbit/s local area network (LAN), differs from the traditional token access method in that the time for the token to walk around the ring is accurately measured by each station and used to determine the usability of the token. FDDI-II, which provides support for isochronous service in addition to the asynchronous and synchronous service provided by FDDI, the media-dependent physical layer (PMD) standard called low-cost fiber PMD (LCF-PMD), and the implementation of FDDI on the synchronous optical network (SONET) are discussed