Mobility management in next-generation wireless systems

The world of wireless telecommunications is rapidly changing. The capabilities of wireless networks are improving at a steady pace. This paper presents two possible protocols for implementing mobility for wireless users in an asynchronous transfer mode (ATM) network. The vision of the authors is of one "wireless ATM telecommunications network" that is capable of supporting a variety of today's applications with room to grow for advanced applications of the future. We first visit database architectures that can support mobility in a wireless ATM network. We then discuss one of two signaling architecture alternatives, the "overlay signaling," for overlay support of mobile users in the ATM-based wireless telecommunications network. "Overlay signaling" aims at minimizing the modification needed to the existing ATM protocols. We then describe a native "migratory signaling" approach that further integrates wireless and wireline users into one global wireless ATM network at the expense of requiring some modifications to the existing ATM protocols. A performance analysis of the proposed signaling architecture alternatives is also presented. We conclude by pointing out some challenges in merging ATM with wireless telecommunications.

The increasing importance of portable computing/telecommunications applications has motivated the studies on broadband wireless network technologies such as wireless ATM (Asynchronous Transfer Mode) or WATM. Orthogonal Frequency Division Multiplexing (OFDM) is especially suitable for high-speed communication due to its resistance to Inter Symbol Interference ISI. This paper describes an ATM network with wireless access for multimedia communications. The network has been specifically designed to serve as a testbed on which evaluate the effect of OFDM wireless channel. The paper overviews and simulates the ATM technology concepts and the requirements of wireless ATM from mobility and modulation technique.

This paper presents a dynamic anchor scheme in wireless ATM (asynchronous transfer mode) networks, which improves the location registers (LR) scheme, in which LR’s are hierarchically structured. This dynamic anchor scheme introduces the CCR (communication-to-computation cost ratio) term in the LR scheme. The proposed scheme reduces computation cost by introducing the active LR. There are at most two active LR’s in a hierarchical arrangement of LR’s and the location of one active LR is static and the location of another active LR called as anchor LR is dynamically selected among the LRs in the hierarchy in order to minimize a total location management cost. The total location management cost is calculated depending on the CCR as well as the CMR (call-to-move ratio). Numerical results show that the proposed scheme can reduce the location management cost compared with the original LR scheme for the different values of the CCR and the CMR.KeywordsWireless ATMLocation Managementanchor scheme

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.

Two major challenges pertaining to wireless asynchronous transfer mode (ATM) networks are the design of multiple access control (MAC), and dynamic bandwidth allocation. While the former draws more attention, the latter has been considered nontrivial and remains mostly unresolved. We propose a new intelligent multiple access control system (IMACS) which includes a versatile MAC scheme augmented with dynamic bandwidth allocation, for wireless ATM networks. IMACS supports four types of traffic-CBR, VBR, ABR, and signaling control (SCR). It aims to efficiently satisfy their diverse quality-of-service (QoS) requirements while retaining maximal network throughput. IMACS is composed of three components: multiple access controller (MACER), traffic estimator/predictor (TEP), and intelligent bandwidth allocator (IBA). MACER employs a hybrid-mode TDMA scheme, in which its contention access is based on a new dynamic-tree-splitting (DTS) collision resolution algorithm parameterized by an optimal splitting depth (SD). TEP performs periodic estimation and on-line prediction of ABR self-similar traffic characteristics based on wavelet analysis and a neural-fuzzy technique. IBA is responsible for static bandwidth allocation for CBR/VBR traffic following a closed-form formula. In cooperation with TEP, IBA governs dynamic bandwidth allocation for ABR/SCR traffic through determining the optimal SD. The optimal SDs under various traffic conditions are postulated via experimental results, and then off-line constructed using a back propagation neural network (BPNN), being used on-line by IBA. Consequently, with dynamic bandwidth allocation, IMACS offers various QoS guarantees and maximizes network throughput irrelevant to traffic variation.

Medical information systems are acquiring the ability to collect and deliver many different types of medical information. In support of the increased network demands necessitated by these expanded capabilities, asynchronous transfer mode (ATM) based networks are being deployed in medical care systems. While ATM supplies a much greater line rate than currently deployed networks, the management and standards surrounding ATM are yet to mature. This paper explores the management and control issues surrounding an ATM network supporting medical information systems, and examines how management impacts network performance and robustness. A multivendor ATM network at the BJC Health System/Washington University and the applications using the network are discussed. Performance information for specific applications is presented and analyzed. Network management's influence on application reliability is outlined. The information collected is used to show how ATM network standards and management tools influence network reliability and performance. Performance of current applications using the ATM network is discussed. Special attention is given to issues encountered in implementation of hypertext transfer protocol over ATM internet protocol (IP) communications. A classical IP ATM implementation yields greater than twenty percent higher network performance over LANE. Maximum performance for a host's suite of applications can be obtained by establishing multiple individually engineered IP links through its ATM network connection.

Future wireless systems will allow a mobile access to Asynchronous Transfer Mode (ATM) networks. Towards this end, one of the main problems is the management of different traffics, each of them having specific Quality of Service (QoS) requirements. This paper proposes a novel Medium Access Control (MAC) protocol coordinated by a controller at the access point. In particular, a polling technique is considered to enable cyclically the transmissions of different terminals. The maximum number of packets that each source can send at each cycle is regulated by a token bucket scheme. We have considered the joint management of real time-Variable Bit Rate (rt-VBR) traffics and bursty Available Bit Rate (ABR) traffics. The controller estimates the congestion of the rt-VBR buffers and accordingly adapts the cycle order. The obtained MAC scheme, called Adaptive Token Bucket – priority based Round Robin (ATB-RR), has permitted to achieve satisfactory QoS levels for both rt-VBR and ABR traffics also in the presence of a scenario with mixed real-time sources.

Future wireless systems will allow a mobile access to Asynchronous Transfer Mode (ATM) networks. This paper proposes a novel Medium Access Control (MAC) protocol based on a round robin policy. A token bucket scheme has been adopted, so that a source enabled to transmit can send a maximum number of packets according to the number of tokens in the related bucket. We have considered real time-Variable Bit Rate (rt-VBR) traffics and bursty Available Bit Rate (ABR) traffics. The scheduler estimates the congestion of the rt-VBR buffers and accordingly adapts the cycle order. The obtained MAC scheme, called Adaptive Token Bucket — priority based Round Robin (ATB-RR), has permitted to obtain satisfactory quality of service levels for both rt-VBR and ABR traffics.

This paper considers the influence of switch fabric design on the performance of resource allocation and connection admission algorithms for asynchronous transfer mode (ATM) networks. In particular, the goal of predictable and guaranteed quality of service (QoS) can be achieved within an ATM network by considering the above factors in the design of the ATM switch fabric. The paper focuses on the identification of the functional requirements of the switch fabric at the ATM layer, and develops an improved architecture which considers QoS at the switch fabric, along with an interface to the resource management. The resultant switch results in ATM networks which have reliable and predictable parameters and which have reduced complexity in connection admission control.

Due to the connection-oriented nature of the asynchronous transfer mode (ATM), one of the challenges in mobile wireless ATM (WATM) systems is the management of terminal handovers. When ATM connections are reestablished to follow terminals moving between areas covered by distinct base stations, seamless handover protocols are necessary to guarantee that ATM cells are delivered to terminals in the correct order, with cell loss rate and delay that satisfy the contracted quality of service (QoS). A promising approach to meet QoS requirements is based on the use of handover buffers at the (destination) base station, where transmitted cells are stored while the connection is being reestablished. Up to date, only simulation and experimental results are available to determine the performance of such protocols and buffering schemes. This paper presents the first attempt to develop an analytical modeling approach to estimate the performance of handover protocols making use of handover buffers at the base station. By incorporating several approximations, the proposed models allow designers to simultaneously take into account numerous system parameters, including handover buffer size, sustainable and peak cell rates of the ATM connection, terminal offered load, and time needed to reestablish the ATM connection. Analytical performance predictions are shown to closely match results of detailed simulation experiments, thus demonstrating the suitability of the proposed modeling framework for the selection of the most adequate solution to handle handover and provide the QoS required by end users.

While the transmission control protocol (TCP) generally provides robust performance across many network environments, several researchers have identified the poor end-to-end performance achieved by TCP on asynchronous transfer mode (ATM) networks. The performance problems arise for several reasons: (1) a size mismatch between TCP segments and ATM cells; (2) the simple protocols used for segmentation and reassembly in ATM, and for retransmission in TCP; (3) specific optimizations in TCP, made primarily for low-bandwidth Internet environments which do not work well in high speed ATM networks; (4) features (or misfeatures) in most TCP protocol implementations; and (5) subtle interactions between all of these factors. This paper describes a simulation model that we have constructed to study TCP performance on ATM networks, as well as a set of simulation experiments conducted using the model. The TCP model is detailed enough to recreate many of the performance problems identified by other researchers, as well as to evaluate potential solutions to the performance problems. The TCP model adds to the traffic modeling toolkit available in our existing ATM network simulator, and enables the further study of performance issues in TCP over ATM.

An asynchronous transfer mode (ATM) network is a high-speed multimedia network which handles various kinds of traffic with different bit-rates and different qualities of service (QoS). In order to maintain the QoS for each traffic source and to avoid possible congestion problems, an ATM network requires highly sophisticated and flexible controllers to insure that this demanding performance can be achieved under unexpected changes in traffic conditions. In this paper, we propose an intelligent architecture using recurrent neural networks and an expert system for traffic control in ATM networks. This traffic control using neural networks is suitable for ATM because neural networks can learn the traffic characteristics and the dynamic changes in the traffic. The proposed mechanism is based on the adaptive prediction of the future values of the traffic and the flow rate for each traffic source. At every given time slot, the controllers in the proposed architecture predict whether the congestion will happen or not and regulate the volume of input traffic for each traffic source before the congestion happens, maintaining the user-required QoS for each traffic source based on the predefined rules. Consequently, the mechanism guarantees the QoS for each traffic source and efficiently prevents congestion.

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.

We propose a congestion control algorithm and design a state feedback controller for regulating the congestion of available bit rate (ABR) traffic in asynchronous transfer mode (ATM) networks. ABR service is specified as the rate-based feedback mechanism for congestion control and provides a control signal to throttled sources from a bottleneck node in order to adjust the throttled source rates based on available capacity. Our main purposes are as follows: (1) to design a state feedback controller; (2) to place the closed-loop poles in any desired regions based on a pole placement constraint; (3) to use the LMI (linear matrix inequalities) approach for finding the optimal state feedback gain K. The simulation results show that, under pole placement and LMI approaches, our state feedback congestion controller for ABR traffic in ATM networks can possibly guarantee the system stability, provide no buffer overflow, determine the optimal source traffic rates and place the closed-loop poles in any desired regions as well.

The Communications Research Laboratory (CRL), Tokyo, Japan, and the Telecommunication Network Laboratory Group, Nippon Telegraph and Telephone Corp., Tokyo, Japan, have developed a highly precise, very long baseline interferometry (VLBI) system using a high speed asynchronous transfer mode (ATM) network. The observed data is transmitted through a 2.488-Gbps ATM network [STM-16/OC-48] instead of being recorded onto magnetic tape. The system was specially designed for the Key Stone Project (KSP), a project begun in 1994 to measure crustal deformation in the Tokyo metropolitan area. Cross-correlation processing and data observations are carried out simultaneously by one operator. It takes about one hour to analyze the data after the observations and correlations are completed. In regular geodetic VLBI experiments run every other day for 24 h, a horizontal position uncertainty of about 2 mm and a vertical position uncertainty of about 10 mm were achieved. The system was designed to enable automated operation throughout the entire process. The results obtained are available to the public via the Internet at http:ksp.crl.go.jp. This system is a significant advance in VLBI and should provide more precise information about crustal deformation in the Tokyo metropolitan area.