Fault-Tolerant Virtual Path Layout in ATM Networks

Broadband networking has evolved dramatically in the past few years. Especially the asynchronous transfer mode (ATM) has attracted attention in the area of high-speed communication, promising the integration of almost all communication profiles such as voice, video and computer-based multimedia communication. As ATM builds the transport technology of broadband integrated services digital network (B-ISDN), it is to be considered as the key technology of the data-highway initiatives aimed by the majority of industrial countries. However, the topic of network security plays an important role in any publicly accessible telecommunication infrastructure. Unfortunately, the progresses made in providing for adequate network security still lag behind the evolution of B-ISDN.In this paper we give an interim report on a project aiming to information privacy in B-ISDN infrastructures. Several approaches to B-ISDN security with emphasis on confidential user-to-user communication are discussed. We compare the different approaches to ATM encryption and propose the application of a method known as ATM cell stream interception. Therefore, we apply an encryption module to an ATM network interface card (NIC) using standardized interfaces and, thus, propose an architecture that is almost independent of the hardware.KeywordsB-ISDN securityATM securityATM cell stream encryption

Broadband Integrated Services Digital Network (BISDN) is conceived as a universal digital network providing both integrated switching and services. Typical services include data, voice, video, high-resolution image, etc. [Spea 87]. Encouraged by developments of fast packet switches [Turn 85] and ATD experiments in France [Deva 88], a packet-oriented virtual circuit transfer mode, called ATM (Asynchronous Transfer Mode), has been adopted as the universal transport vehicle of BISDN services [Minz 89]. Data from various sources are segmented into fixed-size ATM cells and statistically multiplexed to high-speed transmission lines and switches. An ATM cells consists of a 5-octet header and a 48-octet payload fields. Unlike the conventional STM (Synchronous Transfer Mode) technique which switches data according to positions in recurrent structure (frame), ATM cells are switched by labels containing routing information in the headers. Label-based switching is believed to be flexible in integrating diverse traffic types, envisioned for BISDN environments.

High speed Asynchronous Transfer Mode (ATM) wireless networks are assuming a growing interest in the personal communication area [1–6]. This paper describes the design of a wireless ATM system, which is being implemented in the ’’MEDIAN‘‘ project belonging to the European Community (EC) Advance Communications Technologies and Services (ACTS) programme. The Medium Access Control (MAC) aims at providing a simple and efficient transport for ATM cells from a Base Station (BS), interfaced with the ATM Broadband Integrated Service Digital Network (B-ISDN), to ATM Portable Stations (PSs) and vice versa. A Time Division Duplex (TDD) scheme is adopted in which uplink and downlink frame durations can be varied frame-by-frame, in order to fit the present uplink/downlink traffic mix. Moreover, in the uplink, a contention-free based technique is considered in which the slots are assigned to the calls depending on the present load of the PS uplink buffers. The proposed interworking with the ATM network is based on the concept of intercepting the ATM Signalling and Management Cells at the BS, in order to deduce from the ATM Q.2931 messages information relevant to the registration, the call set-up and the MAC procedures.

One of the fundamental challenges facing broadband information transport is to determine congestion control strategies to support multiple classes of traffic in the future asynchronous transfer mode (ATM)-based broadband integrated services digital networks (B-ISDN). To accomplish this in a flexible and a cost-effective manner, priority classes for the different services are commonly used. The authors study priority queueing schemes implemented in a statistical multiplexer with shared and separate buffers, whose input consists of superposition of voice and data traffic. A performance comparison is given for two buffer access schemes: the common nested threshold cell discarding (NTCD) with single shared buffer and NTCD with multiple buffers (NTCD-MB). The arrival process to the multiplexer is approximated using a Markov modulated Poisson process (MMPP). It is shown that when implementing the NTCD-MB priority scheme, the parameters of the switching node can be adjusted in such away that the service quality is guaranteed for different classes of traffic. The improved performance as a result of implementing such scheme is investigated via simulations. >

With networks increasingly moving into virtually every aspect of our daily life, security is gaining importance, not only from the traditional perspective of communication but the network's growing role in modern automation and control. The traditional, certification based approach attempts to guarantee the security of a network through certification. Certified networks are generally confined to a limited domain and, as a result, they are isolated, costly, and under-utilized. In contrast, this paper presents a new principle – user-level, security-on-demand system, wherein the network allocates, where possible, the security resources commensurate with the user's request for transporting message(s) through the network securely. This principle is successfully demonstrated for the current Asynchronous Transfer Mode (ATM) networks, and is the result of an integration of the fundamental framework for network security, recently proposed by the authors in the literature, with the unique characteristics of ATM networks. The framework encapsulates the fundamental knowledge and set of relationships in network security and permits scientific and systematic reasoning about network security. It also enables all user groups – military, government, industry, and academia, to define their security requirements in a uniform manner. The security-on-demand approach promises the development of a "mixed use" class of networks in the future that may be simultaneously shared by different groups of users, with the system sustaining the diverse security requirements of each user. A unique characteristic in ATM network design is the dynamic call setup process. Under it, a network first establishes a virtual path or route for a user's call, guided by the user's requirements, and then transports the messages when a route has been successfully determined. This unique ATM characteristic is integrated with the framework to yield a successful demonstration of the proposed, user-level, security-on-demand approach. Utilizing the security framework as the foundation, every element of the network – node and link, is characterized by a security matrix that reflects its security resources. Every user is permitted to specify the security requirement for the call through a matrix, which expresses the limits of the security resources that the traffic cells must encounter during their transport through the network. Thus, during the dynamic establishment of the virtual path, every node and link is examined to ensure that the user-specified security is met, in addition to bandwidth and other Quality of Service (QoS) requirements. Traffic is launched when the call setup succeeds, otherwise, the call fails. Like all networks, the ATM network inherently consists of geographically dispersed entities and, as a result, the resource allocation strategy is necessarily distributed. Furthermore, as the network operation progresses, the resource availability scene changes dynamically. This paper proposes a unique function that reduces the key network resource parameters at a node to a single value, termed Node Status Indicator (NSI). The NSI value is computed dynamically at every node and disseminated across the network to be utilized by a node to refine its determination of a virtual path for a user call. The aim of the NSI is to improve the resource utilization in the network. The proposed approach is modeled for a large-scale, representative, 40-node ATM network. Utilizing stochastic input traffic that is synthesized to reflect realistic operating conditions, the model is simulated extensively on a testbed of 35+ Pentium workstations, under Linux, configured as a loosely-coupled parallel processor, utilizing an accurate, asynchronous, distributed simulator. The simulator implements the key characteristics of the ATM Forum proposed P-NNI 1.0 and UNI 3.0 standards. While the simulation results reflect a successful realization of the proposed approach, analysis reveals minimal impact of incorporating security on ATM network performance, as measured through call success rates and call setup times. In contrast, the tradition has been to incorporate security into large-scale systems and networks as an afterthought, i.e. adding hardware and software devices after the design has been completed, resulting in performance degradation. Also, while the use of NSI is observed to yield slightly lower average call setup rates and slightly higher average call setup times, a careful analysis of the trace of the calls as they progress through the system, reveals that, in general, calls are dispersed throughout the network, seeking to utilize all available resources of the network more evenly.

The synchronous residual time stamp method (SRTS) is one of the proposed timing recovery methods for constant bit rate (CBR) services over asynchronous transfer mode (ATM) networks. ATM adaption layer 1 (AAL1) is used to specify these CBR services and is usually called the circuit emulation application such as DS1 and DS3. The paper gives both a characteristic and conformance testing method for RTS parameters in a synchronous optical network (SONET) based broadband integrated service digital network (BISDN), which has the reference clock hierarchy derived from a 155.52 MHz network.

Error detection and correction options for data services in B-ISDN (broadband integrated services digital network) are examined. B-ISDN uses the asynchronous transfer mode (ATM) technique for transporting voice, data, and video services. Currently, the ATM cell header size, functions, and adaption layer fields for data services are being standardized in CCITT. Error protection for data payloads will be provided by a per-cell CRC (cyclic redundancy check) field. Different data services may need different degrees of error protection. The authors discuss and analyze different options for error detection and correction by considering various schemes ranging from no error protection to only error detection. Based on the analysis and results presented, a per-cell CRC has been adopted in the adaptation layer for all data services. The per-cell CRC substantially improves cell misdelivery for all data services. For error-insensitive data services, single-bit correction over MID and segment-type fields improves cell loss substantially. At the same time, single-bit correction keeps cell misdelivery sufficiently low (1 in 10/sup 13/ in the worst case). >

The number of Internet users continues to increase due to the popularity of the WWW (World Wide Web). Intranets and extranets have also become very popular as they enable the efficient use of data within companies and enhance business processing speed. IP (Internet protocol) packets are used to realize most of these computer communication services. IP belongs to the network layer in the OSI reference model, so the transfer performance of IP is influenced by the technology used in the data link layer under the network layer. One communication technology for the data link layer is ATM (asynchronous transfer mode). ATM technology was researched and recommended for B-ISDN (broadband integrated services digital network). We have been tackling an Internet/intranet/extranet backbone system that offers high speed, high throughput, small delay and low cost by IP/MAC (media access control) over ATM. However we faced the problem that ATM does not completely suit IP packet and MAC frame transfer. For example, there is the "dead cell problem" in which the loss of even one of the ATM cells forming the IP packet causes the loss of the entire packet. There is also the "cell tax problem", in which the overhead of ATM cells is much larger than those of other long distance transfer techniques. Perfect EPD (early packet discard) is impossible because there is no indication bit that means a cell includes the head or tail part of a datagram in the payload. Moreover, intelligent and effective application use is difficult because the cell header has few CLP (cell loss priority) bits. This paper describes the main problems of datagram transfer across existing ATM networks and details a new cell structure that solves these problems. Other issues relating to this remodelling of the existing cell structure are also examined.

The asynchronous transfer mode (ATM) is well known technology for implementing broadband integrated services digital networks. A major issue in ATM technology is traffic control. We introduce the concepts of conservative cell loss ratio (CLR) estimation and worst case cell arrival patterns, and apply them to cell arrival patterns that conform to the generic cell rate algorithm (GCRA). We define new sets of cell arrival patterns which contain the worst case cell arrival patterns for compliant cell arrival patterns. Based on these sets, we propose a connection admission control method. A numerical example demonstrates its effectiveness.

The paper gives models and analytic techniques for addressing critical issues of the Broadband Integrated Services Digital Network which will use the Asynchronous Transfer Mode. The traffic is expected to be highly bursty and variable at the source and consequently a key issue is admission control. We study a 4-parameter device called a regulator which acts as a policing device as well as a traffic shaper. The device is a generalized leaky bucket with a data buffer, a token buffer supplied by a constant-rate token stream, and a peak rate controller; the outputs of the device are streams of priority and marked cells. The composite system comprising of the source and the regulator is represented in a stochastic fluid model since fluid flow has been found to have properties well matched to the ATM environment, and the Markov Modulated Fluid Source allows bursty characteristics to be accurately modelled. A complete procedure based on spectral expansions for calculating the system's stationary state distribution is given. It is shown that with proper design the regulator effectively controls a three-way trade-off between throughput, delay and burstiness. Numerical results reveal that performance is sensitive to source characteristics such as the squared coefficient of variation of burst and silent periods. The second part of the paper characterizes the output of the regulator. The distributions of the time periods spent in the various states by the output process are calculated exactly. From this an approximate Markovian characterization is obtained. The output streams of priority and marked cells are coupled to capture their correlations. For the simple case of two-state on-off sources, the approximate Markovian characterization of the regulator's output rate processes is explicitly given and it is distinguished by the property that all moments are identical to those of the actual processes. With this characterization an original goal of analyzing a composite system of access regulation and statistical multiplexing is separated, decomposed and thereby made tractable.

The asynchronous transfer mode (ATM) is expected to be the multiplexing and switching technique for the future broadband integrated service digital networks (BISDNs) which can transport almost all types of traffic including bursty data traffic and continuous voice/video frames. However, this capability cannot be realized without a proper congestion-control scheme. This paper discusses the suitability of the real-time channel approach for congestion control in ATM networks. A main contribution of the paper is the development of a new message-transmission scheme for real-time channels which does not require each cell to carry deadline information which is difficult to do with the standard ATM cell format. This makes our scheme compatible with, and implementable in, ATM networks. The new scheme also has a number of advantages over existing ones. The achievable quality of service with the proposed approach would make ATM networks capable of supporting both real-time services and dynamic bandwidth sharing which have been promised but not yet fully realized. >

Management architectures as well as protocols for accessing managed entities and exchanging management information are well developed in standards. On the other hand developments in open distributed processing (ODP) are of recognized importance for network and service management. Their generic features fit well into the geographically extended, multiple vendor and heterogeneous environment of communication networks. As a third ongoing development asynchronous transfer mode (ATM) broadband integrated services digital networks (B-ISDN) offer challenging problems for resource allocation, network performance and quality of service (QoS) evaluation in real time. The paper shows how performance monitoring and evaluation for ATM networks can greatly profit from the features of a distributed system environment (DSE). The extreme flexibility offered by the ATM principle requires a rich and reusable set of servers accomplishing coordinated performance evaluation tests. DSE transparencies are an excellent match to corresponding management applications (MA) requirements, so that tests can be performed in a distributed, flexible and adaptable way under a conceptually simple architecture. The paper draws extensively from a non-distributed counterpart, i.e. an existing sophisticated ATM test and analysis tool developed under the "Research for Advanced Communications in Europe" (RACE) program, R1083 PARASOL project.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The evolution of public telecommunication networks toward broadband integrated services digital networks (B-ISDNs) is presented. The asynchronous transfer mode (ATM), which supports B-ISDNs, and the B-ISDN protocol reference model are discussed. It is shown that the service offered by the ATM layer in the B-ISDN protocol reference model is equivalent to the service offered by the OSI physical layer. It is also shown that the service offered by the ATM adaptation layer (AAL) type 3/4 is similar to an OSI data link service. The emergence of the metropolitan area network (MAN) standard as an intermediate support for broadband services and the similarities between the DQDB MAC and the AAL type 3/4 in its connectionless mode are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Trends in the development of public telecommunication networks

Terminal-pair reliability (TR) in an asynchronous transfer mode (ATM) virtual path (VP) network corresponds to probabilistic quantization of robustness between two VP terminators, given a VP layout and failure probabilities of physical links. Existing TR algorithms are not viable for ATM VP networks owing to either high complexity or failure dependency among the VPs. The paper proposes two efficient algorithms for TR computation between two VP terminators by means of variants of path-based and cut-based partition methods which have been effectively used for TR computation in traditional networks. The first variant, called the path-based virtual path reliability (PVPR) algorithm, partitions the search space based on a physical path embedding the shortest route of VPs from the source to the destination terminator. The second variant, called the cut-based virtual path reliability (CVPR) algorithm, in lieu, performs the partition on the basis of a physical cutset separating the source from the remaining terminators. In both algorithms, each subproblem is recursively processed by means of partition until the source and destination terminators are contracted or disconnected. Experimental results reveal that, CVPR outperforms PVPR with respect to computation time. Moreover, compared to one of the most promising TR algorithms, both CVPR and PVPR exhibit superior performance. The two algorithms and their promising results consequently facilitate the real-time computation of the reliability or robustness of ATM VP networks.