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     

Architectures for ATM network survivability

This article surveys the restoration architectures for asynchronous transfer mode (ATM) network survivability that have been actively studied in this decade. Network reliability is critical for recent and future networks that will advance the information era. Moreover, it is one of the biggest factors in designing and managing networks. Since the early telecom network era, many restoration systems have been developed for plesiochronous digital hierarchy (PDH), synchronous digital hierarchy (SDH), synchronous optical network (SONET), leased lines and so on; and they were surveyed in many papers and books. This article focuses on new restoration techniques for ATM networks. First, the requirement studies are introduced. This includes the scant results published on the influence of failure and the state of failure analysis. Next, restoration schemes are categorized and briefly introduced. Examples include centralized control, automatic protection switch (APS), self-healing ring (SHR), self-healing network (SHN) and failure resistant virtual path (FRVP). In order to achieve adequate restoration probability with minimum cost, a network design scheme is necessary; thus, network design issues are introduced. Finally, this article focuses on the issues, future work, and problems that remain to be solved.     

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     

Self-healing virtual path architecture in ATM networks

ATM network techniques have been actively researched and developed with the goal of realizing B-ISDN. ATM networks can transport signals of various services efficiently and economically, and offer the benefit of enhanced flexibility if the virtual path (VP) concept is adopted. Therefore, the ATM network will provide the infrastructure for B-ISDN. One of the most important themes in B-ISDN is the increased level of network reliability required to to match the high volume of data transmission that will be incurred by the information society and the “mission critical” nature of such data. The authors summarize self-healing network (SHN) schemes they have developed, and discuss problems that must be solved to realize SHN     

A shared-memory virtual channel queue for ATM broadband terminal adaptors

In order to take advantage of the low entry cost of the future public ATM (asynchronous transfer mode) network with shared facilities, it is highly desirable to interconnect different hosts and local area networks (LANs) to the ATM network. The interface between the computer hosts or LANs and the ATM network, commonly called a broadband terminal adaptor (BTA), provides the necessary format conversion for the data packets and the ATM cells. It is conceivable that multiple packets from different virtual channels are interleaved as they arrive at the receive-end BTA. The BTA must have a sufficiently large buffer, called a virtual channel queue (VCQ), to temporarily store the partially received packets. Once a complete packet has been received, it is forwarded to the host or LAN. Whenever the buffer fills with all incomplete packets, a packet must be discarded to make room for others. In this paper, we first study, through computer simulations, the buffer size requirement of a shared-memory VCQ for different numbers of virtual channels at various packet loss probabilities. We then present two different implementation architectures for the shared-memory VCQ, and compare their hardware complexity. The second architecture with linked-queue approach, adopted in our work, requires less buffer and has better scalability to accommodate a large number of virtual channels. Various possible error conditions, such as cell losses in the ATM network and the VCQ buffer overflow, are considered. Corresponding solutions are proposed and included in the VCQ designs.     

The MainStreetXpress core services node-a versatile ATM switcharchitecture for the full service network

Switching systems based on the ATM principle have outgrown the experimental stage, and are already used today in private and corporate networks, as well as in public wide area networks to provide regular service. ATM has the inherent ability to provide a common basis for transmission and switching functionality in both local and wide area networks. With the potential to support all services available today as well as those envisaged for the future, ATM holds a strong promise for network operators and end customers. To fully exploit this potential, ATM switch architectures are required which provide versatility and modularity in supporting services and protocols, independent scalability of data throughput and control performance over a wide range, and also reliability features adaptable to the respective application scenario. This paper describes in some detail how the MainStreetXpress core services node, which has evolved from the prototype described by Fischer et. al. (1991) to a mature central office ATM switch, addresses these issues and provides a future-proof architecture incorporating all of the features required in the B-ISDN era     

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     

Traffic management for B-ISDN services

A set of asynchronous transfer mode (ATM) bearer service categories, differentiated in terms of quality of service (QOS), that will support the large spectrum of applications expected in broadband integrated services digital networks (B-ISDN) is defined. The evolution of applications and the traffic requirements in B-ISDN/ATM networks are described, and the evolution of network services to address these requirements is discussed. The definition of ATM bearer service categories necessary for the economical support of initial applications and evolution to future B-ISDN services is proposed. The elements of the ATM traffic management strategy to support these service categories are presented     

An empirical evaluation of virtual circuit holding time policies inIP-over-ATM networks

When carrying Internet protocol (IP) traffic over an asynchronous transfer mode (ATM) network, the ATM adaptation layer must determine how long to hold a virtual circuit opened to carry an IP datagram. We present a formal statement of the problem and carry out a detailed empirical examination of various holding time policies taking into account the issue of network pricing. We offer solutions for two natural pricing models, the first being a likely pricing model of future ATM networks, while the second is based on characteristics of current networks. For each pricing model, we study a variety of simple nonadaptive policies as well as easy to implement policies that adapt to the characteristics of the IP traffic. We simulate our policies on actual network traffic, and find that policies based on least recently used (LRU) perform well, although the best adaptive policies provide a significant improvement over LRU     

ATM and the future of telecommunication networking

Telecommunication services and networks are in the process of significant change. This paper examines whether asynchronous transfer mode (ATM), thought at one time to be the only viable broadband communication protocol, providing end-to-end connectivity for all applications, still has a role to play in the evolving telecommunication environment. The paper considers the trends in network integration, the emergence of many new services, and the alternative communication protocols with which ATM must compete or interwork. It also addresses the fundamental issue of how to develop a reasonable pricing strategy for these integrated multiservice networks. Several examples are given which show how ATM is adapting to accommodate changing requirements, whilst maintaining its essential ability to transport a diverse range of services. In addition, the authors make a tentative proposal about how economic forces could be harnessed to form a new integrated service model that is compatible with a network infrastructure based upon ATM or any suitable alternative     

Bandwidth allocation and connection admission control in ATMnetworks

Asynchronous transfer mode (ATM) is the transmission format for almost all future communication networks, including broadband integrated services digital networks (B-ISDN). The key feature of ATM is its high flexibility in bandwidth allocation. Instead of reserving capacity for each connection, the bandwidth is allocated on demand. As a consequence, packets (called cells in ATM terminology) might be lost. To guarantee a given quality of service (QoS), some kind of control is needed to decide whether to accept or to reject an incoming connection. A connection is accepted only if the network has sufficient resources to achieve the QoS required by the user without affecting the QoS of the existing connections. In ATM networks, connection admission control (CAC) is responsible for this decision. It is a very complex function because the traffic may vary greatly and have poorly known characteristics. This paper describes CAC procedures proposed in the literature and discusses issues related to bandwidth allocation in ATM networks. It shows that CAC and statistical multiplexing are only needed for certain connections     

Broadband satellite networks-the global IT bridge

Next-generation broadband satellite networks are being developed to carry bursty Internet and multimedia traffic in addition to the traditional circuit-switched traffic (mainly voice) on a global basis. These satellites provide direct network access for personal applications as well as interconnectivity to the terrestrial remote network segments. The main requirement in success of these networks is that they should be able to transmit high data rate traffic with prescribed quality of service (QoS). Thus, the broadband satellite network has no choice other than the rise of ATM technology and to be optimized for Internet-based traffic. ATM is the promising technology for supporting high-speed data transfer potentially suitable for all varieties of private and public telecommunications networks. IP, on the other hand is the fast-growing Internet layer protocol that is applicable over any data link layer Internet-based applications are the emerging source of traffic in the future wireless networks and broadband satellite networks should consider Internet as the primary service. In this paper, we discuss the traditional ATM and wireless ATM networks and explain the characteristics of the wireless IP networks. The paper then uses those concepts in defining the criteria for the broadband satellite networks such as the QoS and traffic management. Application of the broadband satellite networks is also proposed     

ATM in MPLS-based converged core data networks

Services supported by asynchronous transfer mode account for the majority of data and Internet service revenues generated by carrier networks today. This is based on ATM's ability to support high availability services with quality of service. However, the influences of the Internet and a highly dynamic telecommunications market have raised demands for increased flexibility while controlling costs. Therefore, future carrier networks are likely to continue to be based on established technologies, such as ATM, as well as IP. In many cases, this is achieved through maintaining separate ATM and IP core networks, with the IP network supporting Internet services, while the ATM network continues to support guaranteed services such as private lines, broadband access, and video. In some cases, however, it can be advantageous for a carrier to transport segments of their ATM network over their IP network core; for example, to transport ATM traffic currently carried on leased facilities onto an IP network where the service provider owns the facilities. Developments in IP and MPLS-based traffic engineering and QoS may increase the ability of IP-based networks to support ATM services using MPLS. This article provides an overview of approaches enabling a network based on MPLS that naturally supports IP services to also support ATM services. The drivers and requirements for convergence on an IP/MPLS core network are presented, followed by an overview of the different approaches and associated challenges currently being debated in the standards bodies.     

Operations standards for global ATM networks: network element view

The International Telecommunication Union (ITU) has completed work on a series of standards on asynchronous transfer mode (ATM) equipment functional operations and network element management. The objective of these standards is to enable flexible design and interoperability of network elements for use in a global ATM network, independent of any specific implementation. This article discusses these standards with respect to their development and application in planning ATM networks. Specifically, it addresses the following: the modeling approach taken in the development of the ITU standards, key operational features specified in the ATM network element functional model, and the capabilities of the ATM network element management interface. Examples of ATM equipment are provided to illustrate how the functional models specified in the ITU standards may be used by network planners and equipment manufacturers to specify and develop ATM equipment tailored to specific needs, while ensuring network interoperability. The article concludes with some points on the future enhancement of these and related ATM equipment operations standards     

Transport architecture evolution in UMTS/IMT‐2000 cellular networks

Mobile evolution from the second generation (2G) to the third generation (3G) raises several important questions for operators and manufacturers. How to ensure that the old and current investments can still be utilized in the future? What is the optimum architecture? ATM or IP? Voice or data? There is no single correct answer to these questions, as it all depends on individual cases. In this paper, we discuss the transport architecture evolution for the universal mobile telecommunications system (UMTS)/international mobile telecommunications—year 2000 (IMT‐2000), or 3G cellular networks and interworking aspects between 2G and 3G cellular networks. The interfaces between access nodes in a cellular network and the changes incorporated to support packet data services are described. Emerging services such as mobile data, virtual private networks (VPN) and location aware networking are described. Role of ATM and IP in this new transport architecture is presented. Control and data plane interworking issues between different transport technologies are described. The new ATM standard, ATM adaptation layer type 2 (AAL2) and its applicability for transporting compressed speech in an ATM based cellular network is described. A similar approach in IP, multiplexing in real‐time transport protocol (RTP) payload to transport compressed speech on selective interfaces of 3G network, is introduced. Transport network architecture evolution within four different scenarios is evaluated. Special interest is focused on the protocol stacks and flexible layered solutions that allow smooth migration from one transport technology to another. Copyright © 2000 John Wiley & Sons, Ltd.     

在ATM网上实现局域网功能的困难及对策

ＡＴＭ网络作为下一代网络，终将成为网络的主流。但是ＡＴＭ网在目前传统局域网占主导对位的环境条下成为今后的主流和局长的方向，就必须解决二个问题；首先，必须使已有的众多的网络应用软件能在ＡＴＭ工作站上使用；第二，ＡＴＭ网应能很和传统的局 连在一起的工作站一起运作。本文介绍了在ＡＴＭ网上实现局域网功能所面临的困难及一些可能的解决方案。     

Data communications using ATM: architectures, protocols, andresource management

The introduction of ATM is being propelled by the need for fast data communications in public and private networks. What is needed is a clear picture of protocol architectures and traffic characteristics of the various applications to be supported both now and in the future. The authors discuss ATM network architectures with special focus on the support of connectionless LAN interconnection and show which benefits can be obtained from the introduction of a connectionless server in an ATM network. They outline issues related to the use of existing protocols when ATM networks are introduced and show which protocol complexities have to be handled by gateways and servers, again using the example of connectionless LAN interconnection. Having presented network and protocol architectures the issue of data communication in ATM, resource allocation, is treated     

TMN-based broadband ATM network management

ATM has rapidly transitioned from a standards and prototyping concept to become the next-generation switching technology used in products available on the market. With the rapid introduction of ATM switches into networks, there is an urgent need to manage them. The article discusses the telecommunication management network (TMN) interfaces being defined for management systems to communicate with ATM network elements (NEs) and other management systems. ATM management systems will have to communicate with ATM NEs in their jurisdiction using TMN interfaces. Networks will usually contain equipment from different suppliers. Thus, it is vital that there be standard management interfaces so that these different NEs can be managed. Some standard interfaces for ATM networks are defined, while others are being defined. The status of these interfaces is reviewed in the article. Communication between different networks is also needed, both between public networks and between public and private networks. Management personnel of one network need to exchange information with other networks for certain functions (e.g., initial service provisioning), and so management systems of different networks will exchange information through a combination of mechanized and manual interfaces. The status of these interfaces is also reviewed in the article     

Security in data networks

The explosive growth of data networks and their commercial application is driving the need for improved security. This paper aims to raise awareness of the features of secure data networks and the role that encryption plays in this context. An overview of data network security is provided by examining a number of currently available technologies, and how they may be combined to provide a secure network. This is illustrated by a review of existing and proposed encryption services offered by BT/Concert. Taking a glimpse into the future, the ATM Forum's proposals for security in ATM networks are summarised.     

Performance evaluation of TCP extensions on ATM over high bandwidthdelay product networks

Practical experiments in a satellite network environment assist in the design and understanding of future global networks. This article describes the practical experiences gained from TCP/IP on ATM networks over a high-speed satellite link and presents performance comparison studies of such networks with the same host/traffic configurations over local area and wide area networks. These comparison studies on the LAN, WAN, and satellite environments increase our understanding of the behavior of high-bandwidth networks. NASA's Advanced Communications Technology Satellite (ACTS), with its special characteristics and high data rate satellite channels, and the ACTS ATM Internetwork (AAI) were used in these experiments to deliver broadband traffic. Network performance tests were carried out using application-level software (Netspec) on SONET OC-3 (155.52 Mb/s) satellite links. Finally, we experimentally study the performance, efficiency, fairness, and aggressiveness of TCP Reno, TCP New Reno, and TCP SACK end hosts on ATM networks over high BDP networks