Architectures for ATM network survivability and their fielddeployment

Future networks must offer extremely high levels of reliability because information has become critical to the continued well-being of society. This article shows the approaches to the survivable ATM network. The reliability requirements of future networks are discussed first. Development results of three typical restoration architectures (automatic protection switch (APS), self-healing network (SHN), and failure-resistant virtual path (FRVP)) for ATM networks are then shown. Next, we describe current progress in standardization activities. They also discuss open issues that must be resolved in future studies     

Fast restoration of ATM networks

Asynchronous transfer mode (ATM) is now well recognized as the fundamental switching and multiplexing technique for future broadband ISDN. As these networks will be increasingly relied upon for providing a multitude of integrated voice, data, and video services, network reliability is a key concern. There are several intrinsic features of ATM networks that could potentially be exploited to provide improved restoration techniques, beyond those established for synchronous transfer mode (STM) networks, such as digital cross-connect restoration or self-healing rings. These features include ATM cell level error detection, inherent rate adaptation and nonhierarchical multiplexing. The authors explore the use of these features in developing fast restoration strategies for ATM networks. In particular, they address: (1) ATM error detection capabilities for enhanced failure detection, (2) network rerouting strategies, (3) spare capacity allocation, and (4) network control architecture and related implementation aspects. Their findings suggest that fast network span failure detection and bandwidth-efficient rerouting capabilities can be combined to develop restoration strategies for ATM networks with significantly greater performance-cost ratios when compared to existing STM network restoration strategies     

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     

Broadband network restoration

In broadband networks, it is expected that at a given time there will be more data in the network than in narrowband networks, and therefore, to maintain the same quality of service, failures will need to be restored much faster. The purpose of this article is to demonstrate that broadband network technology, and in particular the asynchronous transfer mode (ATM), has factors that enable much faster restoration in broadband networks. These can be summarized as: (i) the higher-speed processing and larger-volume storage possible with today's technology as compared to what was available for narrowband networks, (ii) faster failure detection by making use of ATM cell header error checks, (iii) easier and faster rerouting simply by changing cell headers, (iv) easier and faster splitting of virtual paths by changing cell headers, (v) higher fill factors in the new digital hierarchy due to full termination at cross-connects and switches, and (vi) the statistical multiplexing advantage that can be exploited in a full ATM network configuration. The authors describe four basic characteristics of broadband network restoration, made faster and more efficient because of the factors listed above. These are (i) hitless protection switching, (ii) robust and fast failure detection, (iii) restoration alternatives in broadband networks, and (iv) fast topology update for multiple failures. By employing a combination of these methods, fast restoration of broadband networks can be achieved. The techniques described enable a B-ISDN/ATM network to be constructed that is highly self-healing (i.e., can recover from failures without human intervention) and very fast     

Restoration message transfer mechanism and restorationcharacteristics of double-search self-healing ATM network

The self-healing network is particularly interesting with regard to ATM networks, because the restoration time can be shortened by using the advantages of the ATM network. This paper studies a self-healing ATM network based on virtual path (VP) protection switching. First, a novel self-healing algorithm-the double-search self-healing algorithm-is proposed. It is shown that this algorithm can restore failed bidirectional VPs faster and find alternate VPs more effectively than existing self-healing algorithms. Second, it is shown that the restoration information for self-healing control (SHC) messages must be transferred by specific cells carrying the control and OAM information (Ic&o). Message parameters and a cell format are proposed. Third, evaluation of the restoration characteristics using the proposed self-healing algorithm by computer simulation indicates that good performance against a transmission link failure is obtained even in a large-scale network model with 110 nodes. The results also indicate that the VP group (VPG) method can improve the restoration time without reducing the restoration ratio     

Restoration strategies and spare capacity requirements inself-healing ATM networks

This paper studies the capacity and flow assignment problem arising in the design of self-healing asynchronous transfer mode (ATM) networks using the virtual path concept. The problem is formulated here as a linear programming problem which is solved using standard methods. The objective is to minimize the spare capacity cost for the given restoration requirement. The spare cost depends on the restoration strategies used in the network. We compare several restoration strategies quantitatively in terms of spare cost, notably: global versus failure-oriented reconfiguration, path versus link restoration, and state-dependent versus state-independent restoration. The advantages and disadvantages of various restoration strategies are also highlighted. Such comparisons provide useful guidance for real network design. Further, a new heuristic algorithm based on the minimum cost route concept is developed for the design of large self-healing ATM networks using path restoration. Numerical results illustrate that the heuristic algorithm is efficient and gives near-optimal solutions for the spare capacity allocation and flow assignment for tested examples     

Control protocol and its performance analysis for distributed ATMvirtual path self-healing network

A restorable network comprised of a mesh of ATM virtual paths (AVPs) is expected to be superior to distributed SONET digital cross-connect self-healing networks in terms of restoration time. The paper presents a reliable protocol and evaluation of its performance for control information transfer in distributed AVP self-healing networks. Two error-recovery technologies for the data-link level (selective retransmission and go-back-N) in AVP networks are reviewed, and a model for evaluating the delay of the go-back-N method that has been used in existing terrestrial systems is derived analytically. The proposed analytic model is combined with a self-healing simulator for AVP mesh networks to evaluate the restoration time characteristics. Case study results for the worst-case scenario show that the total restoration time, including link-by-link error control for self-healing control messages, is expected to be less than 2 s, which is the time objective for complete restoration for a metropolitan LATA network. The results also show that the estimated average delay penalty for adding the link-by-link error recovery process is 7.5 ms for complete service restoration     

Self-healing ATM networks based on virtual path concept

This paper proposes self-healing network techniques suitable for ATM networks in order to realize a high-reliablity B-ISDN. First, the characteristics of the virtual paths (VP) and their influence on failure restoration are discussed. A high-speed restoration technique which exploits the benefits of the VP is then proposed and described. The technique simplifies the message transmission processes and reduces the number of generated messages by using preassigned backup virtual paths. Next, the scheme used to design the backup VP routes and spare resource distribution for each link is proposed in order to create a network that applies the proposed restoration scheme. Next, self-reconstruction techniques of backup virtual paths are proposed for the realization of a reversionless restoration cycle. Finally, the feasibility of the distributed control operation is discussed     

A self-healing ATM network based on multilink principles

Self-healing is the ability of a network to reconfigure itself around failures such that calls in progress are not dropped and suffer of no or almost no degradation in quality of service. Providing self-healing capabilities in all parts of the future ATM network in a cost effective way is therefore a key challenge. A new self-healing method based on the multilink concept is presented for dedicated parts of the ATM network, such as, for instance, feeder networks. In the multilink concept that is proposed, the cells of an ATM connection carried by a multilink are distributed over several physical links. If a physical link supporting the multilink fails, the cells will be distributed among the remaining physical links thus providing a self-healing capacity. In this way the quality of service can be maintained at the expense of a higher load on the remaining physical links. The speed of restoration only relies on the detection and signaling of the failure since spare capacity is available on the very multilink. The sharing of spare capacity in addition to the statistical multiplexing gain provides a cost effective self-healing method and leads to a simplified network resource management. The proposed multilink concept is based on an extension of the multipath self-routing concept, which is currently applied by Alcatel in its ATM switching fabric     

A passive protected self-healing mesh network architecture andapplications

The self-healing mesh network architecture using digital cross-connect systems (DCSs) is a crucial part of an integrated network restoration system. The conventional DCS self-healing networks using logical channel protection may require a large amount of spare capacity for network components (such as DCSs) and may not restore services fast enough (e.g., within 2 s). The authors propose a passive protected DCS self-healing network (PPDSHN) architecture using a passive protection cross-connect network for network protection. For the PPDSHN architecture, network restoration is performed in the optical domain and is controlled by electronic working DCS systems. Some case studies have suggested that the proposed PPDSHN architecture may restore services within a two-second objective with less equipment cost than the conventional DCS self-healing network architecture in high-demand metropolitan areas for local exchange carrier networks. The proposed PPDSHN architecture may apply to not only the centralized and distributed control DCS network architectures, but also asynchronous, SONET and ATM DCS networks. Transparency of line rates and transmission formats makes the PPDSHN network even more attractive when network evolution is a key concern of network planning     

Integrated VP-Based Control Strategies for ATM Survivable Networks

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考虑链路负载均衡和容量限制的WDM光传送网保护设计

网络的生存性是WDM光传送网设计时必须考虑的问题.在叠加(Overlay)模式的网络构架中,由于光路之间存在的依赖性,物理网络的单链路失效可能会造成虚拓扑不连通而使上层网络(SDH、ATM或IP)无法使用自身的恢复机制来恢复受影响的业务,因此虚拓扑在嵌入物理拓扑时必须避免发生这种情况.本文提出的VTMPD算法就是针对这一问题的保护设计算法.此算法同时考虑了物理链路的负载均衡和容量限制.我们还给出了VTMPD算法和已有的DAP算法的性能对比,测试数据表明VTMPD算法优于已有的DAP算法.     

A New ATM Self-Healing Algorithm with Back-Routing Capacity

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An overview of broad-band access technologies

The provision of broad-band services based on either the Internet or the asynchronous transfer mode (ATM) technique requires a new generation of access networks. In the short term, solutions such as x-digital subscriber line (DSL) and hybrid fiber coaxial (HFC), allowing the reuse of existing infrastructures look very promising. For the longer term, new infrastructures based either on radio or on optical access links seem preferable. Three x-DSL techniques aiming at high-bit-rate transmission over twisted pairs are presented: high-bit-rate DSL, asymmetrical DSL, and very-high-bit-rate DSL. An extension of existing cable television networks known as HFC is also described. Two other prospective approaches, wireless in the loop (WITL) and fiber in the loop (FITL), are then presented. Several techniques are considered for WITL: digital enhanced cordless telecommunication local multipoint distribution service, wireless ATM, and low Earth orbit satellite constellations. The various architectural alternatives for the FITL approach are discussed, a special interest being dedicated to the synchronous digital hierarchy self-healing loop and the ATM over a passive optical network. We mention the main experiments and the standardization activities inherent to the domain     

Optimal capacity and flow assignment for self-healing ATM networksbased on line and end-to-end restoration

This paper addresses an optimal link capacity design problem for self-healing asynchronous transfer mode (ATM) networks based on two different restoration schemes: line restoration and end-to-end restoration. Given a projected traffic demand, capacity and flow assignment is jointly optimized to find an optimal capacity placement. The problem can be formulated as a large-scale linear programming. The basis matrix can be readily factorized into an LU form by taking advantage of its special structure, which results in a substantial reduction on the computation time of the revised simplex method. A row generation and deletion mechanism is developed to cope with the explosive number of constraints for the end-to-end restoration-based networks. In self-healing networks, end-to-end restoration schemes have been considered more advantageous than line restoration schemes because of a possible reduction of the redundant capacity to construct a fully restorable network. A comparative analysis is presented to clarify the benefit of end-to-end restoration schemes quantitatively in terms of the minimum resource installation cost. Several networks with diverse topological characteristics as well as multiple projected traffic demand patterns are employed in the experiments to see the effect of various network parameters. The results indicate that the network topology has a significant impact on the required resource installation cost for each restoration scheme. Contrary to a wide belief in the economic advantage of the end-to-end restoration scheme, this study reveals that the attainable gain could be marginal for a well-connected and/or unbalanced network     

Future transport network architectures

The architecture of today's long distance transmission networks, which we call the baseline architecture, is a complex and multilayered hierarchy of TDM circuits. One premise of the baseline architecture is that restoration from network failures is provided mostly by SONET/SDH rings. This article presents an alternative architecture that uses ATM and optical layer cross-connect technology for TDM services. Using a sophisticated set of network design tools developed at AT&T Labs-Research, we show that the alternative architecture offers dramatic capital savings and improved network efficiency over the baseline architecture. Most of this savings can be attributed to use of OLXC mesh network restoration, which makes more efficient use of capacity than SONET/SDH rings, and use of ATM switching for transport of TDM circuits, which consolidates the numerous TDM equipment layers inherent to the baseline architecture. In addition, motivated by the rapid growth of IP services, we analyze in the alternative architecture whether to provide restoration for IP services in the IP layer itself, by rerouting packets over precalculated restoration paths with MPLS, or to alternatively provide restoration of failed IP layer links in the OLXC layer. One potential advantage of IP layer restoration is that network operators may choose to only restore a fraction of the services, in particular the “priority” services, affected by a network failure. This article gives some methodology of how to determine this fraction at which IP layer restoration is cost-competitive with OLXC restoration     

OA&M framework for multiwavelength photonic transport networks

Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems     

The Integrated Control-Mechanism in ATM-Based Networks

1 Introduction Network survivability has become a critical issue in telecommunication networks owing to the increase of social dependence on communication systems and the growing importance of information. Fast restoration from a network failure has been …     

Integrity of public telecommunications networks

Provides an overview of the special issue of the IEEE Journal of Communications, Volume 12, Number 1 (January 1994) which addresses open questions in network integrity, reliability and survivability. Current progress in this area is discussed. The questions addressed include user survivability perspectives on standards, planning, and deployment; the analysis and quantification of network disasters; survivable and fault-tolerant network architectures and associated economic analyses; and techniques to handle network restoration as a result of physical damage or failures in software and control systems. Special interests are devoted to the survivability of broadband networks employing the new transport/switching techniques based on the synchronous optical network (SONET) and asynchronous transfer mode (ATM) standards due to their emerging role in future B-ISDN. Network integrity due to failures of common channel signaling (CCS) systems is also very critical. The present special issue includes 22 papers and is organized into the following sections: user perspectives and planning, software quality and reliability, network survivability characterization and standards, network restoration for SONET networks, network restoration for ATM networks, traffic effect and performance enhancement for computer networks, and survivable network design methods. Network restoration methods for SONET, ATM, and computer networks correspond to those for the physical layer (SONET), ATM layer, and the network layer, defined in the CCITT broadband ISDN layer structure     

The Integrated Control-Mechanism in ATM-Based Networks

Survivability is one of the important issues in ATM-based networks since even a single network element failure may cause a serious data loss. This paper introduces a new restoration mechanism based on multi-layer ATM survivable network management architecture. This mechanism integrates the general control and restoration control by establishing the Working VPs logical network, Backup VPs logical network and spare logical network in order to optimally utilize the network resources while maintaining the restoration requirements.