Showing papers in "Telecommunication Systems in 2001"

GRID: A Fully Location-Aware Routing Protocol for Mobile Ad Hoc Networks

Abstract: A mobile ad hoc network (MANET) is one consisting of a set of mobile hosts capable of communicating with each other without the assistance of base stations. One prospective direction to assist routing in such an environment is to use location information provided by positioning devices such as global positioning systems (GPS). In this paper, we propose a new routing protocol called GRID, which tries to exploit location information in route discovery, packet relay, and route maintenance. Existing protocols, as compared to ours, are either not location-aware or partially location-aware in that location knowledge is not fully exploited in all these three aspects. One attractive feature of our protocol is its strong route maintenance capability --- the intermediate hosts of a route can perform a "handoff" operation similar to that in cellular systems when it roams away to keep a route alive. This makes routes in the MANET more stable and insensitive to host mobility. Simulation results show that our GRID routing protocol can reduce the probability of route breakage, reduce the number of route discovery packets used, and lengthen routes' lifetime.

A Dominating-Set-Based Routing Scheme in Ad Hoc Wireless Networks

Abstract: Efficient routing among a set of mobile hosts (also called nodes) is one of the most important functions in ad hoc wireless networks. Routing based on a connected dominating set is a promising approach, where the searching space for a route is reduced to nodes in the set. A set is dominating if all the nodes in the system are either in the set or neighbors of nodes in the set. In this paper, we propose a simple and efficient distributed algorithm for calculating connected dominating set in ad hoc wireless networks, where connections of nodes are determined by their geographical distances. We also propose an update/recalculation algorithm for the connected dominating set when the topology of the ad hoc wireless network changes dynamically. Our simulation results show that the proposed approach outperforms a classical algorithm in terms of finding a small connected dominating set and doing so quickly. Our approach can be potentially used in designing efficient routing algorithms based on a connected dominating set.

Pricing Multicast Communication: A Cost-Based Approach

Abstract: Multicast and unicast traffic share and compete for network resources. A cost-based approach to multicast pricing, based on accurate characterization of multicast scalability, will facilitate the efficient and equitable resource allocation between traffic types. Through the quantification of link usage, this paper establishes a multicast scaling relationship: the cost of a multicast distribution tree varies at the 0.8 power of the multicast group size. This result is validated with both real and generated networks, and is robust across topological styles and network sizes. Since multicast cost can be accurately predicted given the membership size, there is strong motivation to price multicast according to membership size. Furthermore, a price ceiling should be set to account for the effect of tree saturation. This tariff structure is superior to either a purely membership-based or a flat-rate pricing scheme, since it reflects the actual tree cost at all group membership levels.

Atomic Resource Sharing in Noncooperative Networks

Abstract: In noncooperative networks, resources are shared among selfish users, which optimize their individual performance measure We consider the generic and practically important case of atomic resource sharing, in which traffic bifurcation is not implemented, hence each user allocates its whole traffic to one of the network resources We analyze topologies of parallel resources within a game-theoretic framework and establish several fundamental properties We prove the existence of and convergence to a Nash equilibrium For a broad class of residual capacity performance functions, an upper bound on the number of iterations till convergence is derived An algorithm is presented for testing the uniqueness of the equilibrium Sufficient conditions for achieving a feasible equilibrium are obtained We consider extensions to general network topologies In particular, we show that, for a class of throughput-oriented cost functions, existence of and convergence to a Nash equilibrium is guaranteed in all topologies

Practical Time-Scale Fitting of Self-Similar Traffic with Markov-Modulated Poisson Process

Abstract: Recent measurements of packet/cell streams in multimedia communication networks have revealed that they have the self-similar property and are of different characteristics from traditional traffic streams. In this paper, we first give some definitions of self-similarity. Then, we propose a fitting method for the self-similar traffic in terms of Markov-modulated Poisson process (MMPP). We construct an MMPP as the superposition of two-state MMPPs and fit it so as to match the variance function over several time-scales. Numerical examples show that the variance function of the self-similar process can be well represented by that of resulting MMPPs. We also examine the queueing behavior of the resulting MMPP/D/1 queueing systems. We compare the analytical results of MMPP/D/1 with the simulation ones of the queueing system with self-similar input.

Web Server Performance Modeling

Abstract: The advent of Web technology has made Web servers core elements of future communication networks. Although the amount of traffic that Web servers must handle has grown explosively during the last decade, the performance limitations and the proper tuning of Web servers are still not well understood. In this paper we present an end-to-end queueing model for the performance of Web servers, encompassing the impacts of client workload characteristics, server harware/software configuration, communication protocols, and interconnect topologies. The model has been implemented in a simulation tool, and performance predictions based on the model are shown to match very well with the performance of a Web server in a test lab environment. The simulation tool forms an excellent basis for development of a Decision Support System for the configuration tuning and sizing of Web servers.

Finding a Maximal Weighted Independent Set in Wireless Networks

Abstract: This paper introduces MWIS, a distributed algorithm for the efficient determination of a maximal weighted independent set in the topology graph G of a wireless network. Motivated by the observation that the problem of partitioning wireless nodes into clusters easily reduces to the problem of finding a maximal weighted independent set of nodes, the proposed algorithm is described by taking into account two main characteristics of wireless networks, namely, the broadcast nature of the wireless medium and the possibility to support nodes mobility. MWIS is executed at each node by means of fast message triggered procedures that require the sole knowledge of the topology local to the node. Moreover, its time complexity is proven to be bounded by a topology dependent parameter of the network (the stability number ?(G) of the network topology graph G), rather than by the invariant number n of the network nodes. Based on this result, and by using a well known result about ?(G) in the theory of random graphs the paper concludes with a brief discussion on the average time complexity of MWIS.

GPS/Ant-Like Routing in Ad Hoc Networks

Abstract: A mobile ad hoc network (MANET) is comprised of mobile hosts that can communicate with each other using wireless links. In this paper we present a novel routing algorithm called GPSAL (GPS/Ant-Like Routing Algorithm) which is based on GPS (Global Positioning System) and mobile software agents modeled on ants for routing in ad hoc networks. We compare our algorithm to the Location-Aided Routing (LAR) [20] algorithm for MANET which is also based on GPS. Simulation results show that our algorithm has less overhead than LAR.

Route Maintenance in a Wireless Mobile Ad Hoc Network

Abstract: A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, without the infrastructure of base stations. To deal with the dynamic changing topology of a MANET, many routing protocols have been proposed. In this paper, we consider the route maintenance problem, which includes two parts: route deterioration and route breakage. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route once it is discovered, until it is expired or broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability. So the routing paths can be adjusted on-the-fly while they are still being used for delivering packets and can be patched in minimum wireless bandwidth and delay while route errors occur.

Fault-Tolerant Multistage Interconnection Network

Abstract: In this paper, a new fault-tolerant Banyan (FTB) network design is proposed. The rules to add extra hardware and links to the regular Banyan network in order to get the new FTB network are presented. The work includes a modular design for a new 2×2 switch element that can be configured in different well-defined modes. In case an error occurs in the function of a switch in the FTB network, the switch can be bypassed and other switch in the network replaces its role. The most attractive feature of the new design is that it can maintain the original (regular) Banyan topology in the presence of faults. Consequently, the system performance will not be affected due to the occurrence of tolerable faults in the interconnection network. This feature makes our design different from all fault-tolerant designs. Moreover, multiple faults can be tolerated in the proposed FTB network. The FTB network will be very powerful in safety critical systems and applications where error can lead to catastrophic events.

An Evaluation of Scenario Notations for Telecommunication Systems Development

Abstract: The elicitation, modeling and analysis of requirements have consistently been one of the main challenges during the development of complex systems. Telecommunication systems belong to this category of systems due to the worldwide distribution and the heterogeneity of today’s telecommunication networks. Many proposals have been made for approaches that allow the developer to describe system behavior. Scenarios and use cases represent one such approach that has become popular for the capturing and analysis of requirements. However, little research has been done that compares different approaches and assesses their suitability for the telecommunications domain. This paper defines evaluation criteria for scenario notations and then uses these criteria to review twelve scenario notations. In addition, nineteen approaches for the construction of more detailed and integrated design models from scenarios are briefly compared. Such models enable further analysis and pave the way towards automated generation of implementations. Hopes and challenges related to scenario-based development of telecommunication systems are finally discussed.

Contradictory relationship between Hurst parameter and queueing performance (extended version)

Abstract: Long Range Dependent (LRD) network traffic does not behave like the traffic generated by the Poisson model or other Markovian models. From the network performance point of view, the main difference is that LRD traffic increases queueing delays due to its burstiness over many time scales. LRD behavior has been observed in different types and sizes of networks, for different applications (e.g., WWW) and different traffic aggregations. Since LRD behaviour is not rare nor isolated, accurate characterization of LRD traffic is very important in order to predict performance and to allocate network resources. The Hurst parameter is commonly used to quantify the degree of LRD and the burstiness of the traffic. In this paper we investigate the validity and effectiveness of the Hurst parameter. To this end, we analyze the UCLA Computer Science Department network traffic traces and compute their Hurst parameters. Queueing simulation is used to study the impact of LRD and to determine if the Hurst parameter accurately describes such LRD. Our results show that the Hurst parameter is not by itself an accurate predictor of the queueing performance for a given LRD traffic trace.

A Nonstationary Offered-Load Model for Packet Networks

Abstract: Motivated by the desire to appropriately account for complex features of network traffic revealed in traffic measurements, such as heavy-tail probability distributions, long-range dependence, self similarity and nonstationarity, we propose a nonstationary offered-load model. Connections of multiple types arrive according to independent nonhomogeneous Poisson processes, and general bandwidth stochastic processes (not necessarily Markovian) describe the individual user bandwidth requirements at multiple links of a communication network during their connections. We obtain expressions for the moment generating function, mean and variance of the total required bandwidth of all customers on each link at any designated time. We justify Gaussian approximations by establishing a central limit theorem for the offered-load process. We also obtain a Gaussian approximation for the time-dependent buffer-content distribution in an infinite-capacity buffer with constant processing rate. The offered-load model can be used for predicting future bandwidth requirements; we then advocate exploiting information about the history of connections in progress.

Quality-of-Service Analysis for Statistical Multiplexing with Gaussian Distributed and Autoregressive Input

Abstract: We investigate multiplexers in telecommunication systems with a workload process developing equivalent to that of a service system with semi-Markovian input, which includes fluid flow and time slotted systems. Discrete time methods are used to analyze their waiting time and loss rate. Our focus is on the performance evaluation of statistical multiplexing. Traffic flows are modeled by autoregressive processes producing autocorrelated and Gaussian distributed workload increases. The superposition of on-off voice sources approaches autoregressive processes and they also serve as a basic model for video traffic in an appropriate time scale, although video reveals a more complex autocorrelation structure. Performance results are obtained depending on only two parameters, which allow for clear conclusions about the statistical multiplexing gain with regard to bounds on loss rates as demanded in quality-of-service guarantees.

Link Capacity Sharing between Guaranteed- and Best Effort Services on an ATM Transmission Link under GoS Constraints

Abstract: While link allocation policies in multi-rate circuit switched loss models have drawn much attention in recent years, it is still an open question how to share the link capacity between service classes in a fair manner. In particular, when an ATM link is offered calls from service classes with/without strict QoS guarantees one is interested in link capacity sharing policies that maximize throughput and keep the per-class blocking probabilities under some GoS constraints. In this paper we propose a model and associated computational technique for an ATM transmission link to which CBR/VBR and ABR classes offer calls. We also propose a simple link allocation rule which takes into account blocking probability constraints for the CBR/VBR calls and a throughput constraint for the ABR calls and attempts to minimize the blocking probability of ABR calls. Numerical examples demonstrate the effectiveness of the policy and of the applied computational technique.

ATM Network Design: Traffic Models and Optimization-Based Heuristics

Abstract: We consider the design and capacity expansion of ATM networks as an optimization problem in which flows representing end-to-end variable bit-rate services of different classes are to be multiplexed and routed over ATM trunks and switches so as to minimize the costs of additional switches and transport pipes while meeting service quality and survivability constraints. After an overview of the underlying fractional Brownian motion model for aggregate flows, a nonlinear multicommodity optimization problem is formulated and LP-based heuristics for its approximate solutions are described. Finally, computational results are produced that demonstrate realistic size problems can be solved with the proposed method to shed light on key economic characteristics of ATM traffic, such as safe levels of statistical multiplexing, as well as robust and efficient design alternatives.

The BMAP/G/1 Queue with Level-Dependent Arrivals --- An Overview

Abstract: The BMAP/G/1 queue is a field of intensive research since several years. We generalize the BMAP/G/1 queue by allowing the arrival process to depend on the state (level) of the queue, i.e., on the number of customers in the system. This will be called a BMAP/G/1 queueing system with level-dependent arrivals. A suitable arrival process is defined by nesting a countable number of BMAPs. We give conditions for the level-dependent BMAP/G/1 queue to be stable, i.e., in equilibrium. By analysing the fundamental periods, which now depend on their starting level, we determine the stationary queue length at service completion times and at an arbitrary time.

Blocking of Dynamic Multicast Connections

Abstract: Multicast connections have a bandwidth saving nature. This means that a multicast connection --- in taking the form of a tree with streams merging at the nodes --- requires much less capacity from the network links than a bunch of separate point-to-point connections providing the same connectivity. In this paper, we consider dynamic multicast connections that can be used to model, for example, TV or radio delivery on a telecommunications network, such as an ATM network with virtual circuits. We show how to calculate the blocking probabilities of requests to join such a tree. First, we consider the blocking probabilities occurring in a single link. The resulting model is able to capture heterogeneous capacity requirements for different multicast channels. Then we extend the results to a whole network using the reduced load approximation. The accuracy of the approximation method is studied by simulations.

State-Dependent Pricing and Its Economic Implications

Abstract: In a packet-switched network, the service provider can charge users a state-dependent price, which depends on the extent to which the network is congested. Alternatively, one can charge users a long-term average price, which is set based on expected demand and capacity availability, but independent of instantaneous network conditions. In this paper, we compare the benefits of different pricing schemes from the service provider, society, and consumer perspectives. Our results suggest that adopting state-dependent pricing improves both profit and total benefits to the society, but may be detrimental to consumer benefits.

Geographical Reservation for Guaranteed Handover and Routing in Low Earth Orbit Constellations

Abstract: In this paper, we address the problem of permanent guaranteed routing through a LEO satellite constellation with inter-satellite links. A reduction to a geometric problem of intersection of rectangles is given, along with algorithmic issues. We express the problem on a very simple model, and discuss the extension to more complicated schemes. We present some experimental results based on this framework that demonstrate the efficiency of the method in a call admission control process.

Optimizing the Number of Robots for Web Search Engines

Abstract: Robots are deployed by a Web search engine for collecting information from different Web servers in order to maintain the currency of its data base of Web pages In this paper, we investigate the number of robots to be used by a search engine so as to maximize the currency of the data base without putting an unnecessary load on the network We use a queueing model to represent the system The arrivals to the queueing system are Web pages brought by the robots; service corresponds to the indexing of these pages The objective is to find the number of robots, and thus the arrival rate of the queueing system, such that the indexing queue is neither starved nor saturated For this, we consider a finite-buffer queueing system and define the cost function to be minimized as a weighted sum of the loss probability and the starvation probability Under the assumption that arrivals form a Poisson process, and that service times are independent and identically distributed random variables with an exponential distribution, or with a more general service function, we obtain explicit/numerical solutions for the optimal number of robots to deploy

Dual Ascent for Uncapacitated Telecommunications Network Design with Access, Backbone, and Switch Costs

Abstract: We consider the telecommunications network design problem of simultaneously determining at which locations to place a switch, interconnecting all switches with backbone trunks, and connecting each location to some switch by an access circuit We assume there are no capacity constraints, and minimize the sum of switch, backbone trunk, and access circuit costs using a dual ascent method that solves a sequence of dual uncapacitated facility location problems A Steiner tree based heuristic provides a primal feasible design On 15 random problems with 100 locations, the average duality gap is 20%

Integration of Dispatch and Interconnect Traffic in a Land Mobile Trunking System. Waiting Time Distributions

Abstract: The performance evaluation of integrated dispatch and interconnect traffic schemes are important in land mobile trunking system. Two such schemes have been analyzed by different methods. We present an unified approach to analyze various new schemes for integrating dispatch and interconnect traffic. Waiting time distribution under the First-In-First-Out (FIFO) discipline for dispatch calls, and lost probability for interconnect calls are obtained. Performance tradeoff between dispatch and interconnect traffic are displayed.

Variable Bit Rate Voice Using Hysteresis Thresholds

Abstract: In this work we address the problem of statistically multiplexing a variable number of telephone calls via a limited number of channels. Terminals operate with voice activity and silence detectors, and the speech is encoded to a bit rate which is system state dependent. Growing from zero, calls in the system are admitted with a maximum bit rate (maximum quality) until the cutoff fraction of talkspurt (a front end clipping) reaches a certain threshold. At this point the voice bit rate of all transmitting terminals is reduced. If due to traffic fluctuations, the number of calls in progress decreases, then all voice terminals are allowed to operate at the maximum bit rate again. In order to avoid annoying effects to listeners, both the percentage of voice information that is lost and the mean number of changes in the bit rate per mean call holding time are constrained. The first constraint is strongly dependent on the encoding bit rate, and the second one is controlled by using a hysteresis threshold when switching from one bit rate to another. In this work we have used three encoding bit rates, high, medium and low. A birth---death Markov process is used to model the system, which provided exact numerical evaluations for the percentage of time the system operates in each encoding bit rate and for the mean number of changes in the bit rate. Metrics are defined to measure the percentage of both types of voice information that are lost (not transmitted), cutoff or front end clipping and uniform dropping. Finally, an illustrative example is reported.

Forecasting Demand for Telecommunications Products from Cross-Sectional Data

Abstract: A crucial planning problem for many telecommunications companies is how best to forecast changes in demand for their products over the next several years. This paper presents a new approach to demand forecasting that performs well compared to even sophisticated time series methods but that requires far less data. It is based on the following simple idea: Divide units of analysis (census blocks, customers, etc.) into groups with relatively homogeneous behaviors, forecast the behavior of each group (which can be done easily, by construction), and sum over all groups to obtain aggregate forecasts. Identifying groupings of customers to minimize forecast errors is a difficult combinatorial challenge that we address via the data-mining technique of classification tree analysis. Product acquisition rates are modeled as transition rates in a multi-state simulation model. The dynamic simulation model is used to integrate the transition rate and covariate information and to predict the resulting changes in product demands over time.

Call admission control for capacity-varying networks

Abstract: Many networks, such as Non-Geostationary Orbit Satellite (NGOS) networks and networks providing multi-priority service using advance reservations, have capacities which vary over time for some or all types of calls carried on these networks. For connection-oriented networks, Call Admission Control (CAC) policies which only use current capacity information may lead to excessive and intolerable dropping of admitted calls whenever the network capacity decreases. Thus, novel CAC policies are required for these networks. Three such CAC policies are discussed, two for calls with exponentially distributed call holding times and one for calls whose holding time distributions have Increasing Failure Rate (IFR) functions. The Admission Limit Curve (ALC) is discussed and shown to be a constraint limiting the conditions under which any causal CAC policy may admit calls and still meet call dropping guarantees on an individual call basis. We demonstrate how these CAC policies and ALC represent progressive steps in developing optimal CAC policies for calls with exponentially distributed call holding times, and extend this process to the more general case of calls with IFR call holding times.

Loss characterization in high-speed networks through simulation of fluid models

Abstract: This paper describes the design principles of a fluid-based, discrete-event simulator and its application to the characterization of losses in ATM networks. This simulation technique allows us to obtain performance measures that either cannot be found using known analytical methods or for which a conventional simulation is too expensive; notably, fluid-model simulation makes it feasible to characterize for a given buffer its occupation, duration of congestion periods, frequency of loss bursts and loss-burst volume in fairly complex networks. Several numerical examples illustrate the proposed simulation method.

Resource Sharing for Book-Ahead and Instantaneous-Request Calls Using a CLT Approximation

Abstract: This paper extends the admission control algorithm for book-ahead and instantaneous-request calls proposed by Greenberg, Srikant and Whitt (1997) to cover multiple classes of instantaneous-request calls, each with their own traffic characteristics and their own performance requirements. As before, book-ahead calls specify their starting and finishing times, and are assumed to book far ahead relative to the holding times of the instantaneous-request calls. The book-ahead calls may be constrained by an upper-limit on the capacity that can be reserved for them. Instantaneous-request calls are admitted if the probability of interruption (or some other form of service degradation in response to the conflict) for that call is below a threshold, but now this threshold can be class-dependent, and now the interrupt probability is calculated by a normal approximation based on the central limit theorem. Simulation experiments show that the normal approximation performs as well as the previous detailed calculation in single-class examples, and that the normal approximation can be applied to multi-class examples.

Optimal Policies for ATM Cell Scheduling and Rejection

Abstract: This paper addresses the following questions related to buffer management schemes for high speed integrated services networks: (i) given the pattern of cell arrivals from different classes of traffic, can buffer control significantly influence the effect of cell loss, and (ii) what are the "best" policies for selecting cells for transmission from buffers in the network nodes as well as for rejecting cells when the buffers are full. The basic approach to answering these questions is to impute a cost of losing cells which could depend on the class of application, and to minimize this cost over the finite or infinite time horizons. The policies we derive using this cost minimization approach are best in the sense that they minimize linear cost functions of cell losses, at each instant of time during the system's operation. We also show how to construct policies that minimize general cost functions of cell loss rates.

A Probabilistic Study of Inter-Satellite Links Load in Polar Orbit Satellite Constellations

Abstract: We analyze the load of the inter-satellite links in polar satellite constellations. Starting from simple considerations on the structure of the underlying network topology, we derive the probability of use of different families of links, with various hypotheses on the nature of the traffic. Our analysis leads to a simple, practical evaluation of the asymptotical link load, which depends on the position of the link. Our model is validated through a constellation simulator, which shows that the results hold even for light load.