ATM Node Research Articles

Physical-Layer p-Cycles Adapted for Router-Level Node Protection: A Multi-Layer Design and Operation Strategy

We study an idea for efficient integrated protection of an IP over WDM network using the spare capacity of span-protecting p-cycles to provide protection against both optical link failures and router node failures in the IP/MPLS layer. Previously, networks using span-protecting p-cycles were designed from the point of view of a single-layer physical transport network. Also separately, it has been known how to plan capacity allocations to IP-layer logical links to support controlled levels of bandwidth oversubscription on transiting traffic flows through a failed router or ATM node. To address both failure types, however, it is unattractive to simply combine the two investments in added protection capacity. Accordingly, we have studied ways to plan a 100% span-restorable set of physical-layer p-cycles so that very high levels of transiting traffic flow can also be restored upon MPLS router node failure, with controlled worst-case oversubscription of LSP capacity allocations. In test cases it was found that the spare capacity provided by span-protecting p-cycles can provide a high level of node protection depending on the strategy used for exploring the p-cycle capacity. We think this leads to novel and efficient strategies for multi-service and multi-layer survivable traffic engineering and bandwidth management

A predictive dynamic output buffer reconfiguration (PDOBR) architecture for ATM networks

The traditional output buffer architecture in ATM switches is realized in one of two forms – shared or separate. In the shared design, all of the N output links utilize a large common buffer, of size S cells, in an effort to achieve efficient use of the total buffer space. Under the separate buffer architecture, distinct buffers, each of size S N cells, are assigned to every output link, the goal being to realize fair buffer usage by every individual output link. For both architectures, however, the buffer organization is determined, permanently, at the time of the switch fabric design, and may not be altered during actual operation. The highly dynamic and stochastic nature of ATM traffic poses a key difficulty for this tradition. This paper introduces a radically new approach, termed Predictive Dynamic Output Buffer Reconfiguration (PDOBR) architecture, wherein the output buffer organization in the switch fabric is reconfigured dynamically, i.e., during network operation, under the call processor’s control, such that the network incurs minimal cell drop stemming from buffer overflow. Under PDOBR, the output buffer at every node of the ATM network is organized in the form of separate buffers for each output link, of size S N cells, plus a “floating” buffer of the same size, that may be appended, at runtime, to any one of the output links to augment its net buffer capacity. In contrast to the shared buffer that experiences severe congestion and gross unfairness under bursty traffic, separate buffers result is fairness in buffer availability between the output links, yielding efficient behavior. Utilizing its knowledge of the successful user call requests and the magnitudes of the corresponding sustained cell rate (SCR) bandwidth requests, the call processor at every ATM node computes the net bandwidth commitment for each of its output links through a simple summation of the corresponding SCR values. The call processor then compares the net bandwidth commitment for every output link against an empirical threshold, obtained through systematic analysis, to predict and identify a single output link, if any, that is likely to incur relatively high cell traffic. The “floating” buffer is then appended to the output link prior to launching the corresponding user’s traffic. Experiments confirm logical thinking that an increase in the size of the “floating” buffer should result in a superior efficiency for PDOBR. Further analysis reveals that a combination of faster technology, FAST Schottky TTL, and a threshold setting of 70 Mb/s yields a very high throughput of 85.05% and low cell drop rate of 14.95%. However, the highest performance is achieved – namely a high throughput of 91.56% coupled with a low cell drop rate of 8.44%, when the “floating” buffer size is increased by 18.98%, the difference, Δ L 2, in the absolute cell drop rates resulting from 70 Mb/s and 100 Mb/s threshold scenarios, and the threshold is set at 70 Mb/s.

Reactive congestion control algorithm in an ATM node

This paper discusses the congestion phenomenon on anAtm node and presents an analytical approach to follow the cumulated delays on the network. It proposes an adaptation algorithm of the sources rate with the evolving congestion state of a node by a reactive approach.

Crankback Prediction in Hierarchical ATM Networks

When an ATM node discovers that it cannot continue the setup of a virtual channel under the requested Quality of Service (QoS), it initiates a backtracking procedure called “crankback.” We propose a novel scheme, referred to as crankback prediction, that decreases the crankback overhead. Under the proposed scheme, nodes check during the connection admission control procedure whether the establishment of a virtual channel has a good chance to be admitted over the entire designated route. If this is not the case, crankback is initiated even before a particular QoS parameter is violated. The main idea behind the proposed scheme is to allocate a “quota” to the Peer Groups (PGs) along the message path, and then to suballocate this quota to the child PGs of these PGs. This process continues recursively until reaching the 1-level PG, which contains only physical nodes. The main advantage of the proposed scheme is that it lowers the setup delay and the processing and communication load imposed by signaling messages that establish unused portions of Virtual Channels (VCs)

Adaptive crankback schemes for hierarchical QoS routing in ATM networks

To reduce routing information and achieve scalability in large ATM networks, ATM Private Network-to-Network Interface (PNNI) adopts hierarchical routing. For efficient routing, a large ATM network is decomposed into subnetworks called Peer Groups (PG), which advertise aggregated routing information only. Because of lack of precision in the aggregated information, a call set up message on a chosen route can be rejected. When an ATM node discovers that a call set up message cannot proceed due to insufficient resources, a back-tracking procedure called ‘crankback’ is initiated against call blocking. Although crankback reduces blocking probability, it also causes additional overhead, such as longer setup delay. Consequently, this study proposes two approaches to reduce crankback overhead. The first approach adds extra information to the setup message, referred to as Crankback Information Stack (CIS), to reduce crankback overhead. Meanwhile, the other approach, referred to as Cost Threshold (CT), uses the aggregated path cost and the cost information of previously rejected call setup message to determine whether call setup should be tried on the next alternate path. The simulation results herein demonstrate that both of the proposed approaches significantly reduce crankback overhead, while the combination of the CIS and CT approach achieves further improvement.

Data communication management in system specification

In this paper, a powerful communication scheme is introduced to efficiently meet different communication requirements for behavioural synthesis from VHDL. The algorithmic description of the system behaviour is specified through a set of cooperating VHDL processes. Communication between processes is provided by the definition of a message-passing communication scheme, to efficiently manage both synchronised and unsynchronised data exchange. A way to effectively map message passing to shared memory for system synthesis is also presented. The proposed data communication scheme has been successfully tested with the VHDL model of the congestion control of an ATM node.

11-4 TV信号切換システム用ATMノード開発

11-4 TV信号切換システム用ATMノード開発

Large scale enterprise ATM node with per-VC traffic control

On the backbone nodes of enterprise networks which handle data and voice traffic, complicated Quality of Service (QoS) capability, transmission efficiency, and high reliability are required. ATM technology satisfies those requirements. We have developed a large scale enterprise ATM node based on the shared buffer switch architecture. In the node, per-VC traffic control functions are implemented at low cost using centralized control of buffer write and read. In this paper, we explain the detail of the per-VC traffic control functions and show the performance results of ABR control using the node.

Low-bit-rate voice and telephony over ATM in cellular/mobile networks

A new ATM AAL2 to support low-bit-rate and delay-sensitive applications in an ATM environment has been approved by the ITU-T and ATM Forum. AAL2 allows multiplexing of voice/data packets (minicells) from different users in a single ATM connection, thus improving the utilization of the network resources. This article identifies issues related to AAL2 such as the application environment, the gain obtained by multiplexing voice packets from different users on a single ATM connection, buffer requirements, and cell assembly delay. To analyze these issues, we modeled and simulated ATM trunking between a base transceiver station and the mobile switching center. The performance simulations show that the multiplexing gain obtained by AAL2 is significant, and the output buffer requirement at the ATM node is small. In addition, the results show that a timeout mechanism is needed to limit the ATM cell assembly delay in order to meet the delay requirements of real-time traffic such as voice.

A Fundamental Framework for Network Security Towards Enabling Security on Demand in an ATM Network

The traditional, certification based approach attempts to guarantee the security of a network through risk analysis that involves the static analysis of the risks, threats, resource availability, cost, and other parameters. Certified networks are generally confined to a limited domain and, as a result, they are isolated, costly, and under-utilized. This paper integrates the recently introduced fundamental framework for network security with the fundamental and unique characteristics of ATM networks towards a new paradigm-user level security on demand. The framework approach has been adopted by the US National Security Agency as the basis for its Network Rating Model. The framework consists of eight perspectives and nine attributes. The perspectives, termed pillars in this paper, individually provide orthogonal views of network security and collectively constitute a comprehensive stable structure that supports the total network security. The attributes refer to the inherent characteristics of a secure network. The framework provides a basis to address, fundamentally, every weakness in a given network. It also enables the understanding of the security posture of an individual network, in a comprehensive manner, the comparative evaluation of the security of two or more networks, and the determination of the resulting security of a composite network that is formed from connecting two or more networks with known security. In the proposed security on demand approach, the security posture of every node and link is computed, utilizing the framework. Under call setup, the ATM network allows the system to configure, i.e. first project and then verify through propagating a setup message containing a DTL (designated transit list), a route from the source to the destination, including every intermediate ATM node and link, that meets the requirements of every user. Every user specifies the appropriate elements of a security matrix that represents the desired security requirements, in addition to the usual bandwidth and other quality of service (QoS) requirements. Traffic is launched when the call setup succeeds, otherwise, the call fails. Thus, the approach is consistent with the basic characteristics of, is fundamentally the most logical approach to security in, and offers comprehensive security in ATM networks. It also views security as a distributed network resource and allocates it to each user efficiently, based on demand and dictated by the need. The approach has been integrated into the call admission control (CAC) algorithm of the ATM Forum proposed Private Network-Network Interface (PNNI), modeled for a representative, 50-node ATM network, and an asynchronous distributed simulation is executed on a testbed of 25+ Pentium workstations under Linux, configured as a loosely-coupled parallel processor. While the success of the implementation validates the approach, the asynchronous distributed simulation closely resembles an operational ATM network. Performance results, obtained utilizing stochastic and representative input traffic, reveal that the overhead of integrating security into CAC is negligible.

CELL-LOSS-RATIO ANALYSIS WITH INSUFFICIENT KNOWLEDGE OF TRAFFIC CHARACTERISTICS

This paper evaluates cell-loss ratio in an output buffer of an ATM node based on the observed relative frequency of the number of cell arrivals during a fixed interval. The central issue of this evaluation problem is that the unique evaluation result of cell-loss ratio cannot be derived because the relative frequency of the number of cell arrivals does not completely describe the traffic characteristics of cell streams. Thus! this paper focuses on the derivation of the worst-case performance, that is, the cell-loss-ratio upper bound. Two cell-loss-ratio upper bounds are derived - one for when the cell streams are stationary, and one for when cell streams are stationary and ergodic. Numerical results show that cell streams with the same relative frequency of the number of cell arrivals can have quite different cell-loss ratios, and that the derived formula gives the actual upper bounds.

Simple schemes for traffic integration at call set-up level in ATM networks

The paper presents a scheme for admission control at call set-up level at an ATM node. The traffic is considered to be divided into classes, characterized by statistical parameters like peak and average bandwidth, and by Quality of Service (QoS) requirements that allow us to define a ‘feasibility region’ where such requirements are guaranteed. A model to describe the ‘call admission’ is proposed. Then, three alternative strategies to get the maximum number of acceptable connections, by taking into account the probability of blocking a call at the call set-up level, are described. The first one is intended to minimize the overall call blocking probability; the second one is aimed at balancing the probability among the different traffic classes; while the last one allows us to enforce a constraint on the call blocking probability. The efficiency of the proposed strategies is tested by simulation and verified by comparing it with other admission control schemes that appear in the literature.

Burst reducing servers in ATM networks

We study a stream of traffic or message as it is transferred over an ATM connection consisting of burst reducing servers. A message is modeled as a deterministic fluid flow, and an ATM node is modeled as a server which allocates bandwidth to messages. A message's burstiness curve b(μ) is the buffer size needed to prevent cell loss if it is served at rateμ. A server is burst reducing if its output message is always less bursty than the input message. Two popular bandwidth allocation schemes — the fixed rate and the leaky bucket server — are shown to be burst reducing. We also present a new class of burst reducing servers, the affine servers. We derive buffer requirements along a multi-hop connection and the final fluid flow reaching the destination as a message goes through a sequence of burst reducing servers. Finally, we suggest an approach to defining service quality.

A new approach for allocating buffers and bandwidth to heterogeneous, regulated traffic in an ATM node

A new approach to determining the admissibility of variable bit rate (VBR) traffic in buffered digital networks is developed. In this approach all traffic presented to the network is assumed to have been subjected to leaky-bucket regulation, and extremal, periodic, on-off regulated traffic is considered; the analysis is based on fluid models. Each regulated traffic stream is allocated bandwidth and buffer resources which are independent of other traffic. Bandwidth and buffer allocations are traded off in a manner optimal for an adversarial situation involving minimal knowledge of other traffic. This leads to a single-resource statistical-multiplexing problem which is solved using techniques previously used for unbuffered traffic. VBR traffic is found to be divisible into two classes, one for which statistical multiplexing is effective and one for which statistical multiplexing is ineffective in the sense that accepting small losses provides no advantage over lossless performance. The boundary of the set of admissible traffic sources is examined, and is found to be sufficiently linear that an effective bandwidth can be meaningfully assigned to each VBR source, so long as only statistically-multiplexable sources are considered, or only nonstatistically-multiplexable sources are considered. If these two types of sources are intermixed, then nonlinear interactions occur and fewer sources can be admitted than a linear theory would predict. A qualitative characterization of the nonlinearities is presented. The complete analysis involves conservative approximations; however, admission decisions based on this work are expected to be less overly conservative than decisions based on alternative approaches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hierarchical dynamic control of multiple traffic classes in ATM networks

AbstractA hierarchical control structure is proposed to ensure performance requirements and to maintain load balancing among different traffic classes at an ATM node. A two‐level control hierarchy is defined, where one level performs fixed class‐selective call admission control strategies that are periodically dynamically coordinated by a higher level bandwidth allocation controller. The call admission control rules are designed to maintain a certain grade of service, in terms of cell loss probability, given the buffer space and bandwidth (percentage of cells) assigned to each class. The assignment of buffers is performed off‐line, whereas bandwidth shares are periodically recomputed on‐line by the allocation controller, that attempts to minimize a cost function, accounting for overall cell loss and refused traffic. The bandwidth assignments obtained are passed to the call admission controllers, where they are used as parameters affecting the admission rules until the next intervention. The control structure, the strategies and the optimization algorithm used are described in detail, as well as the assumptions underlying the choices that have been made. Simulation results are reported and discussed.

Multiplexing digital television sources on ATM networks

This paper investigates the transmission of digital television signals on ATM networks. The key characteristic of an ATM network is its ability of statistically multiplexing variable bit rate sources in queueing systems called multiplexers. These queues are optimally located at the output port of the switching fabrics and emptied at constant bit rate by the destined transmission links. In that framework, the paper intends to analyze the multiplexing of digital television sources which are connected at a given ATM node and share the same transmission resources. Consequently, the study starts with analyzing the packet traffic generated when pooling television sources. The paper proceeds with modeling the queue behaviors and, eventually, with deriving the multiplexing performances. These latter parameters refer to three main topics namely, the cell losses and their configurations, the transmission jitter and the statistical multiplexing. Both theoretical approaches and simulations are employed to yield the final performances. As an important issue, substantial multiplexing gains is also put into evidence through theoretical and experimental arguments. Cell loss configurations are presented to suggest what policy to implement for cell loss burst correction. It is further shown how random transmission delay and jitter turn out to be minor problems when dealing with the transmission of television services.

Performance design of an ATM node on the basis of the experience from the BLNT RACE project

AbstractThis paper contains recent results of ATM traffic studies obtained by the project partners involved in the Broadband Local Network Technology (BLNT) RACE project 1012. These studies are concerned with congestion notification methods, problems in conjunction with Peak Cell Rate control and the analysis of multi‐stage switching systems. The implications of these studies on the design and performance of an ATM node are discussed.

A simulation study of bursty data traffic with hybrid source smoothing in an ATM node

In this paper, we study the mean delay and maximum buffer requirements at different levels of burstiness for highly bursty data traffic in an ATM node. This performance study is done via an event-driven simulation program which considers both real-time and data traffic. We assume that data traffic is loss-sensitive. A large buffer (fat bucket) is allocated to data traffic to accommodate sudden long burst of cells. Real-time traffic is delay-sensitive. We impose input traffic shaping on real-time traffic using a leaky-bucket based input rate control method. Channel capacity is allocated based on the average arrival rate of each input source to maximize the utilization of channel capacity. Simulation results show that both the maximum buffer requirements and mean node delay for data traffic are directly proportional to the burstiness of its input traffic. Results for mean node delay and cell loss probability of real-time traffic are also analyzed. The simulation program is written in C++ and has been verified using the zero mean statistics concept by comparing simulation results to known theoretical or observed results.

Terminals and signal processing in atm networks

The paper presents the research topics of the «Progetto Finalizzato Telecomunicazio-ni» partially founded by CNR (National Council for Research) on the multi-media terminals, video broadcast terminal and HDTV (High Definition Television) signal processing. It describes the main features of a full ATM Workstation, of ISDN multiservice terminal and digital video broadcast codec connected to ATM node. It presents also the studies on HDTV by simulation of algorithm.

A self‐learning control of atm service quality using neural network

AbstractStudies of ATM network are conducted aiming at the integrated processing of multimedia. One of the important problems is to find a control method for the ATM network which can meet various types of requirements for the service quality arising from the diversity of sources connected to the network. For such a problem, the traditional approach by exhaustive analysis and simulation that has been used in the circuit switching network has a problem in that a large number of parameters to be considered in the ATM network complicates the control and it is difficult to deal flexibly with the diversity of sources and the change of traffic characteristics due to the new service.The leaky pattern table method is proposed which can realize a highly accurate control by learning from the data with small generation rate. As an example of application of the proposed method, the call admission control in the ATM node is considered. The detailed construction of the control system is discussed, and the proposed system is evaluated by computer simulation using a basic model.From such a viewpoint, this paper applies the neural network which can realize a high‐speed learning of the multiinput/multi‐output nonlinear function by back propagation to obtain the relation between the load in the ATM network and the communication quality by training. This network is used also to effect the learning control to deal flexibly with the change of the environment.