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Selected Areas in Communications, IEEE Journal on

Issue 7 • Date Sept. 1995

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Displaying Results 1 - 19 of 19
  • Fundamental design issues for the future Internet

    Page(s): 1176 - 1188
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    The Internet has been a startling and dramatic success. Originally designed to link together a small group of researchers, the Internet is now used by many millions of people. However, multimedia applications, with their novel traffic characteristics and service requirements, pose an interesting challenge to the technical foundations of the Internet. We address some of the fundamental architectural design issues facing the future Internet. In particular, we discuss whether the Internet should adopt a new service model, how this service model should be invoked, and whether this service model should include admission control. These architectural issues are discussed in a nonrigorous manner, through the use of a utility function formulation and some simple models. While we do advocate some design choices over others, the main purpose here is to provide a framework for discussing the various architectural alternatives.<> View full abstract»

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  • An algorithm for combined cell-site selection and power control to maximize cellular spread spectrum capacity

    Page(s): 1332 - 1340
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    There is much current interest in spread spectrum wireless mobile communications and in particular the issue of spread spectrum wireless capacity. We characterize spread spectrum cellular capacity and provide a combined power control, cell-site selection algorithm that enables this capacity to be achieved. The algorithm adapts users' transmitter power levels and switches them between cell-sites, and it is shown that the algorithm converges to an allocation of users to cells that is optimal in the sense that interference is minimized. The algorithm is decentralized, and can be considered as a mechanism for cell-site diversity and handover. We provide numerical examples to show how effectively the algorithm relieves local network congestion, by switching users in a heavily congested cell to adjacent, less congested cells View full abstract»

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  • Feedback-based flow control of B-ISDN/ATM networks

    Page(s): 1252 - 1266
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    We consider a system comprising of a single bottleneck switch/node that is fed by N independent Markov-modulated fluid sources. There is a fixed propagation delay incurred by the traffic between these sources and the switch. We assume that the switch sends periodic feedback in the form of a single congestion indicator bit. This feedback also incurs a fixed propagation delay in reaching the sources. Upon reaching the sources (or the access controllers associated with the sources), this congestion indicator bit is used to choose between two rates for the excess traffic, high or low, possibly depending on the state of that source. The switch employs a threshold mechanism based on its buffer level to discard excess traffic. We show that the stationary distribution of this system satisfies a set of first-order linear differential equations along with a set of split boundary conditions. We obtain an explicit solution to these using spectral decomposition. To this end we investigate the related eigenvalue problem. Based on these results we investigate the role of delayed feedback vis-a-vis various time-constants and traffic parameters associated with the system. In particular, we identify conditions under which the feedback scheme offers significant improvement over the open-loop scheme View full abstract»

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  • Billing users and pricing for TCP

    Page(s): 1162 - 1175
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    This paper presents a system for billing users for their TCP traffic. This is achieved by postponing the establishment of connections while the user is contacted, verifying in a secure way that they are prepared to pay. By presenting the user with cost and price information, the system can be used for cost recovery and to encourage efficient use of network resources. The system requires no changes to existing protocols or applications and can be used to recover costs between cooperating sites. Statistics collected from a four-day trace of traffic between the University of California, Berkeley, and the rest of the Internet demonstrate that such a billing system is practical and introduces acceptable latency. An implementation based on the BayBridge prototype router is described. Our study also indicates that pricing schemes may be used to control network congestion either by rescheduling time-insensitive traffic to a less expensive time of the day, or by smoothing packet transfers to reduce traffic peaks View full abstract»

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  • Connection establishment in high-speed networks

    Page(s): 1150 - 1161
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    The evolving view of connection establishment for connection-oriented services in high-speed networks such as ATM involves a contract negotiation process between a user agent and a network agent. The first stage consists of separate roles for the user and the network. The user agent must characterize the information streams that will be transmitted and the performance parameters that define the desired quality of service for that user. Similarly, the network agent must determine the network's resources and its capabilities to accommodate various mixes of service types. The second stage involves negotiations between multiple network and user agents, in which the parties agree to set up connections to transmit the agreed information streams in a manner to guarantee the agreed qualities of service, and at agreed prices. We focus on these two stages that together form the connection establishment process. After this process, during the connection, the network must police the user to determine compliance with the information stream characteristics, and must implement flow control, service priority mechanisms and packet multiplexing disciplines as necessary to guarantee the quality of service View full abstract»

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  • Stochastic control of handoffs in cellular networks

    Page(s): 1348 - 1362
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    A dynamic programming formulation is used to obtain an optimal strategy for the handoff problem in cellular radio systems. The formulation includes the modeling of the underlying randomness in received signal strengths as well as the movements of the mobile. The cost function is designed such that there is a cost associated with switching and a reward for improving the quality of the call. The optimum decision is characterized by a threshold on the difference between the measured power that the mobile receives from the base stations. Also we study the problem of choosing the “best” fixed threshold that minimizes the cost function. The performance of the optimal and suboptimal strategies are compared View full abstract»

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  • Architecting noncooperative networks

    Page(s): 1241 - 1251
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    In noncooperative networks users make control decisions that optimize their individual performance measure. Focusing on routing, two methodologies for architecting noncooperative networks are devised, that improve the overall network performance. These methodologies are motivated by problem settings arising in the provisioning and the run time phases of the network. For either phase, Nash equilibria characterize the operating point of the network. The goal in the provisioning phase is to allocate link capacities that lead to systemwide efficient Nash equilibria. The solution of such design problems is, in general, counterintuitive, since adding link capacity might lead to degradation of user performance. For systems of parallel links, it is shown that such paradoxes cannot occur and that the optimal solution coincides with the solution in the single-user case. Extensions to general network topologies are derived. During the run time phase, a manager controls the routing of part of the network flow. The manager is aware of the noncooperative behavior of the users and makes its routing decisions based on this information while aiming at improving the overall system performance. We obtain necessary and sufficient conditions for enforcing an equilibrium that coincides with the global network optimum, and indicate that these conditions are met in many cases of interest View full abstract»

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  • A framework for uplink power control in cellular radio systems

    Page(s): 1341 - 1347
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    In cellular wireless communication systems, transmitted power is regulated to provide each user an acceptable connection by limiting the interference caused by other users. Several models have been considered including: (1) fixed base station assignment where the assignment of users to base stations is fixed, (2) minimum power assignment where a user is iteratively assigned to the base station at which its signal to interference ratio is highest, and (3) diversity reception where a user's signal is combined from several or perhaps all base stations. For the above models, the uplink power control problem can be reduced to finding a vector p of users' transmitter powers satisfying p⩾I(p) where the jth constraint pj⩾Ij(p) describes the interference that user j must overcome to achieve an acceptable connection. This work unifies results found for these systems by identifying common properties of the interference constraints. It is also shown that systems in which transmitter powers are subject to maximum power limitations share these common properties. These properties permit a general proof of the synchronous and totally asynchronous convergence of the iteration p(t+1)=I(p(t)) to a unique fixed point at which total transmitted power is minimized View full abstract»

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  • The effect of bandwidth allocation policies on delay in unidirectional bus networks

    Page(s): 1309 - 1323
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    We consider the problem of allocating bandwidth fairly to each node in a shared, unidirectional bus network. We focus on the pi persistent protocol, since these are open loop policies designed to operate well in high speed networks, which have a very large bandwidth-delay product and feedback in the upstream direction is not available in a timely manner. First, we introduce an improvement to the basic pi persistent protocol, in which we replace random coin tosses with a deterministic counting algorithm, and thereby reduce the delays for all nodes for any given choice of {pi}. We then describe an exact method for calculating average packet delays and queue lengths in both the pi persistent and our new deterministic n out of m protocols, based on the regenerative approach of Georgiades et al. (1987). These delay results, together with simulation measurements, show that both of these protocols still waste some bandwidth. After presenting a lower bounding argument to show that some wasted bandwidth is inevitable in all such distributed access control schemes, assuming a passive bus without feedback in the upstream direction, we show that changing the bus to unidirectional point-to-point links between (very simple) active interfaces at each node allows us to construct distributed access schemes that require no upstream feedback and are both work conserving and fair. To illustrate how this can be done, we introduce the pi preemptive protocol, in which each node randomly inserts its own packets into the traffic arriving from upstream. We derive a simple and effective heuristic for calculating the preemption probability for each node, and use simulation to show how well it equalizes the delays at each node View full abstract»

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  • Optimal buffer sharing

    Page(s): 1229 - 1240
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    We address the problem of designing optimal buffer management policies in shared memory switches when packets already accepted in the switch can be dropped (pushed-out). Our goal is to maximize the overall throughput, or equivalently to minimize the overall loss probability in the system. For a system with two output ports, we prove that the optimal policy is of push-out with threshold type (POT). The same result holds if the optimality criterion is the weighted sum of the port loss probabilities. For this system, we also give an approximate method for the calculation of the optimal threshold, which we conjecture to be asymptotically correct. For the N-ported system, the optimal policy is not known in general, but we show that for a symmetric system (equal traffic on all ports) it consists of always accepting arrivals when the buffer is not full, and dropping one from the longest queue to accommodate the new arrival when the buffer is full. Numerical results are provided which reveal an interesting and somewhat unexpected phenomenon. While the overall improvement in loss probability of the optimal POT policy over the optimal coordinate-convex policy is not very significant, the loss probability of an individual output port remains approximately constant as the load on the other port varies and the optimal POT policy is applied, a property not shared by the optimal coordinate-convex policy View full abstract»

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  • Network programming methods for loss networks

    Page(s): 1189 - 1198
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    This paper describes how some of the insights available from the stochastic analysis of dynamic routing may be incorporated into the classical mathematical programming approach to the design of networks. In particular, we present the results of a number of numerical investigations into network architectures for circuit-switched communication networks. Our investigations use recent theoretical results integrating network flow optimization and Markov decision processes to provide performance bounds for dynamic routing strategies. Following a tutorial introduction of the above mentioned topics we develop a sequence of network examples. Our first examples are familiar ones, such as symmetric fully connected networks and networks with moderate amounts of asymmetry, and we describe how network programming methods complement earlier work on dynamic routing. We then consider a variety of example networks which have a more sparse collection of links. These examples indicate the potential applicability of the methods to a variety of areas, including studies of the design, performance and resilience of future communication networks View full abstract»

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  • A new feedback congestion control policy for long propagation delays

    Page(s): 1284 - 1295
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    This paper presents a new feedback congestion control mechanism for the flow control of the best-effort available bit rate (ABR) traffic in ATM networks. This new mechanism belongs to the class of feedback control schemes that ensure no data losses and operate based on simple `stop' and `start' signals. A novelty presented by this paper is a methodology which, for a given set of desired properties, leads to the specification of the corresponding control algorithm. For the case of a single connection, the algorithm can operate with the theoretically minimum possible buffer size. Interestingly, the algorithm obtained has a different structure than the previous schemes; it does not operate based on fixed high and low thresholds. A new congestion control mechanism is subsequently derived for the flow control of multiple connections. The new scheme is exercised hop-by-hop and on a per-connection basis. This scheme allows connections to share memory and bandwidth resources efficiently within the network. The performance of the new scheme is also presented, and its statistical multiplexing efficiency is demonstrated. The measures investigated include buffer occupancy, average delay, overhead due to the protocol signals, and sustained throughput. In the case of long propagation delays, the buffer savings achieved by the new scheme are substantial View full abstract»

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  • A protocol for random multiple access of packets with mixed priorities in wireless networks

    Page(s): 1324 - 1331
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    Random multiple access (RMA) protocols comprise an important class for the accessing/signaling stage in multimedia ATM wireless networks. Within the RMA class, the ALOHA algorithm is most widely used at this point in time, while, as is well known, the latter algorithm becomes unstable, as the user population increases. In this paper, we consider the part-and-try algorithm, instead, for a system with different priorities. Based on this algorithm, we construct a mixed priority protocol whose total throughput-for all priorities combined-equals 0.487. In the special and important for ATM case of two, low, and high priorities, with respective Poisson intensities λL and λH. We also present an analytical methodology which allows the computation of the average packet delays as functions of the rates λL and λH View full abstract»

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  • Optimal flow control of a stochastic fluid-flow system

    Page(s): 1219 - 1228
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    This paper is concerned with the optimal flow control of an ATM switching element in a broadband-integrated services digital network. We model the switching element as a stochastic fluid-flow system with a finite buffer, a constant output rate, and Markov-modulated fluid input. There is a cost of holding fluid and a reward for admitting the fluid to the buffer. We study the optimal flow control policies that minimize the fetal expected discounted cost. We analyze the problem by two different approaches and show that the optimal policy is of the turnpike type with the turnpike levels dependent on the states of the Markov-modulated source. We also state sufficient conditions under which the optimal turnpike levels are monotonic functions of the states of the Markov-modulated source View full abstract»

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  • Adaptive algorithms for feedback-based flow control in high-speed, wide-area ATM networks

    Page(s): 1267 - 1283
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    This paper gives a class of flow control algorithms for the adaptive allocation of bandwidths to virtual connections (VC) in high-speed, wide-area ATM networks. The feedback rate to the source from the network is parsimonious, with each feedback bit indicating whether the buffer at a distant switch is above or below a threshold. The service discipline at the switch is first-come-first-served. The important goal of adaptability aims to make all of the network bandwidth available to the active VCs, even though the number of such VCs is variable over a given range. Each VC has two parameters, one giving its minimum guaranteed bandwidth and the other is the weight for determining its share of the uncommitted bandwidth. Judicious selection of these parameters defines distinctive services, such as best effort and best effort with minimum bandwidth. We derive design rules for selecting the parameters of the algorithms such that the appropriate guarantees and fairness properties are exhibited in the dynamical behavior. The systematic use of “damping” in right proportion with “gain” is shown to be a powerful device for stabilizing behavior and achieving fairness. Our analyses are based on a simple analytic fluid model composed of a system of first-order delay-differential equations, which reflect the propagation delay across the network. Extensive simulations examine the following: (1) fairness, especially to start-up VCs; (2) oscillations; (3) transient behavior, such as the rate of equalization from different initial conditions; (4) disparate bandwidth allocations; (5) multiple paths with diverse propagation delays; (6) adaptability and robustness with respect to parameters; and (7) interoperability of different algorithms View full abstract»

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  • Analysis of controlled multiplexing systems via numerical stochastic control methods

    Page(s): 1207 - 1218
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    The paper demonstrates the usefulness of numerical methods of stochastic control theory for the design, analysis and control of multiplexing type systems and networks, as well as ATM type systems. The sources are of the Markov-modulated type, although the final results hold for other types (e.g. low-order AR schemes). Control problems arise when we wish to control cell loss due to buffer overflows by regulating the sources. The basic control mechanism is the deletion of selected low-priority cells, according to an appropriate state dependent rule. But the same results hold for many other schemes (e.g. purchasing incremental bandwidth). By exploiting the large size of the system (large number of users), the systems can be efficiently approximated by diffusion type processes, whether there is a control term or not, and for many types of control mechanisms. The basic controls are of the “low-priority cell deletion” type, and various extensions. They might be state dependent, and we can obtain optimal controls for cost functions that weigh buffer overflow, controller cell deletion loss as well as queue length. The limit equations are an effective aggregation of the original system. It is shown that there are substantial savings in losses with the use of optimal control techniques. The numerical methods can be used to balance the losses at the control with those due to buffer overflow, to minimize losses at the controller subject to constraints on buffer overflow, and to explore various approximations, systems aggregations, the interaction of multiple source classes of different priorities View full abstract»

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  • On the message and time complexity of protocols for reliable broadcasts/multicasts in networks with omission failures

    Page(s): 1296 - 1308
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    This paper presents a fundamental study on the message and time complexity of reliable broadcast/multicast protocols in point-to-point networks subject to omission failures. We assume a weakly synchronous model in which there is a known upper bound on the delay in delivering a message from one process to another. A faulty process may omit sending or receiving messages; this characterizes a common faulty behavior in networking applications. We focus our study on the number of messages and the maximum amount of time required of any fault-tolerant protocol in failure-free executions. We present protocols that, in an n-process network subject to at most t faulty processes, guarantee the delivery of a message from any process to all other nonfaulty processes. In particular, when no failure occurs in the network, our protocols require (n+t-1) messages and at most (n-1+upper bound [log2(t+1)])·δ units of time, where δ is the maximum time required to deliver a message from a process to another. Moreover, we show that our protocols are optimal with respect to message and time complexity. The new insights provided by the lower bound proofs yield a graph-theoretic characterization of all message and time optimal reliable broadcast/multicast protocols in failure-free executions. We further discuss the implications of our results on the support of multicast services in high-speed switching networks such as ATM View full abstract»

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  • A new degree of freedom in ATM network dimensioning: optimizing the logical configuration

    Page(s): 1199 - 1206
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    A mathematical model is presented that provides a well-defined formulation of the logical configuration problem of ATM networks (the carriers of future B-ISDN) with the objective of maximizing the total expected network revenue, given the physical network parameters and the traffic requirements of each virtual subnetwork. A two-phase solution procedure is developed in which the decision variables are the logical link capacities that specify the logical decomposition into virtual subnetworks, and the load sharing parameters. The first phase of the solution finds a global optimum in a rougher model. The second phase uses this as an initial point for a gradient-based hill climbing that applies the partial derivatives of the network revenue function obtained in a more refined model View full abstract»

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  • Pricing congestible network resources

    Page(s): 1141 - 1149
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    We describe the basic economic theory of pricing a congestible resource such as an FTP server, a router, a Web site, etc. In particular, we examine the implications of “congestion pricing” as a way to encourage efficient use of network resources. We explore the implications of flat pricing and congestion pricing for capacity expansion in centrally planned, competitive, and monopolistic environments. The most common form of Internet pricing is pricing by access, with no usage-sensitive prices. With a fixed set of users, we expect to see greater capacity when usage is not priced, but also greater congestion. However, with greater congestion, congestion-sensitive users might not use the resource View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

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Editor-in-Chief
Muriel Médard
MIT