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Communications Magazine, IEEE

Issue 3 • Date March 2005

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Displaying Results 1 - 25 of 29
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  • Fiber optic cable infrastructure and dispersion compensation for storage area networks

    Page(s): 86 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (839 KB) |  | HTML iconHTML  

    The fiber optic cable infrastructure currently used by many large data centers is over 10 years old, and may soon require upgrading in order to support higher-data-rate services. Legacy multimode optical fiber is typically low bandwidth, and will only support limited distances at data rates exceeding 1 Gb/s. In this article we investigate various methods for extending the distance of multimode fiber at higher data rates. This includes the tactical use of enhanced bandwidth multimode fiber, electronic dispersion compensation, and wavelength tuning control loops. View full abstract»

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  • Reliability and availability assessment of storage area network extension solutions

    Page(s): 80 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    Reliability is one of the key performance metrics in the design of storage area network extensions as it determines accessibility to remotely located data sites. SANs can be extended over distances spanning from hundreds to thousands of kilometers with optical or IP-based transport networks. The network equipment used depends on the storage protocol used for the extension solution. The present article provides analytical models developed for the calculation of long-term average downtimes, service failure rates, and service availability that can be achieved as a function of hardware/software failures, software upgrades, link failures, failure recovery times, and layer 3 protocol convergence times. View full abstract»

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  • Multifractal based network traffic modeling [Book Review]

    Page(s): 12 - 14
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    Freely Available from IEEE
  • Reconfigurable free-space optical cores for storage area networks

    Page(s): 93 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1200 KB) |  | HTML iconHTML  

    The role of the optical storage area network is becoming increasingly important in computer network architectures, with the amount of information being presented and requested on the Internet ever increasing. One of the key questions is what is the role of, and how do we control, an optical switch core within a SAN to optimize its performance. In this article we review two potential optical switch technologies and assess their performance as a SAN optical switch core. View full abstract»

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  • Communication paradigms for sensor networks

    Page(s): 116 - 122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    When compared with now classical MANETs, sensor networks have different characteristics, and present different design and engineering challenges. One of the main aspects of sensor networks is that the solutions tend to be very application-specific. For this reason, a layered view like the one used in OSI imposes a large penalty, and implementations more geared toward the particular are desirable. This survey presents the three main paradigms for communication in ad hoc networks and discusses their applicability for routing, querying, and discovery. We conclude that the node-centric approach, although the oldest and best understood, is not the most appropriate for large-size low-energy application-specific sensor networks. View full abstract»

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  • Game theory models for IEEE 802.11 DCF in wireless ad hoc networks

    Page(s): S22 - S26
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    Because wireless nodes decide their channel accesses independently in the IEEE 802.11-based ad hoc networks, and the channel access of a node has an influence on those of its neighboring nodes, game theory naturally becomes a useful and powerful tool to research this kind of network. In this article a game model is proposed to interpret the IEEE 802.11 distributed coordination function mechanism. In addition, by designing a simple Nash equilibrium backoff strategy, we present a fairness game model. Our simulation results show that the new backoff strategy can improve TCP performance almost perfectly. View full abstract»

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  • A centralized energy-efficient routing protocol for wireless sensor networks

    Page(s): S8 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (533 KB) |  | HTML iconHTML  

    Wireless sensor networks consist of small battery powered devices with limited energy resources. Once deployed, the small sensor nodes are usually inaccessible to the user, and thus replacement of the energy source is not feasible. Hence, energy efficiency is a key design issue that needs to be enhanced in order to improve the life span of the network. Several network layer protocols have been proposed to improve the effective lifetime of a network with a limited energy supply. In this article we propose a centralized routing protocol called base-station controlled dynamic clustering protocol (BCDCP), which distributes the energy dissipation evenly among all sensor nodes to improve network lifetime and average energy savings. The performance of BCDCP is then compared to clustering-based schemes such as low-energy adaptive clustering hierarchy (LEACH), LEACH-centralized (LEACH-C), and power-efficient gathering in sensor information systems (PEGASIS). Simulation results show that BCDCP reduces overall energy consumption and improves network lifetime over its comparatives. View full abstract»

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  • Performance evaluation of multihop ad hoc WLANs

    Page(s): 107 - 115
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    Ongoing technological advances in portable devices, coupled with the need for continuous connectivity while mobile, have made ad hoc networks a compelling research and development topic, particularly in a challenging multimedia multihop scenario. The ability of IEEE 802.11's ad hoc mode of operation, as a dominating wireless local area network (WLAN) protocol, to serve multihop networks requires thorough investigation. In this article, through considering crucial real-life physical phenomena and avoiding as many confining assumptions as possible, system performance measures such as delay and packet failure rate are evaluated. As a result, the importance of adequate selection of the system parameters toward performance improvement is underscored. Moreover, the simulation results imply that by complementing through priority provisions, coordination, route reservation, clustering, and optimum channel coding considerations, the IEEE 802.11 medium access control (MAC) protocol can survive in a multihop scenario. The custom simulation environment developed features modularity, comprising traffic generator, mobility, wireless channel, and IEEE 802.11 protocol modules, and is capable of accommodating many more of the physical phenomena involved. View full abstract»

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  • Next-generation optical storage area networks: the light-trails approach

    Page(s): 72 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB) |  | HTML iconHTML  

    Multiple architectures, technologies, and standards have been proposed for storage area networks, typically in the WAN environment. The transport aspect of storage signifies that optical communications is the key underlying technology. The contemporary SAN over optical network concept uses the optical layer for pure transport with minimal intelligence. This leads to high cost and overprovisioning. Future optical networks, however, can be expected to play a role in optimizing SAN extension into the WAN. An essential characteristic of SAN systems is tight coupling between nodes in a SAN network. Nodes in a SAN system have two critical functions that are presently emulated by data layers and can be offloaded to the optical layer. First, nodes need to signal among each other to achieve tasks such as synchronous and asynchronous storage. Second, to benefit from an optimized network, nodes need to allocate bandwidth dynamically in real time. In this article we show how the optical layer can be furthered from just pure transport to creating opportunities in provisioning as well as providing the mirroring function of SAN systems (multicasting) and consequently lead to reduction in cost. We demonstrate that the light-trail model is one way of efficiently utilizing the optical layer for SAN. View full abstract»

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  • Regulatory and policy issues protecting public safety with better communications systems

    Page(s): 10 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB) |  | HTML iconHTML  

    The communications failure present in the September 11 World Trade Center tragedy served as the basis for this paper. These communications failures are not the result of simple operator error or a single design flaw. The problems are rooted in the basic technical architecture of the communications infrastructure used for public safety in the United States, and the policy that produced that infrastructure. This paper presents innovation in both technology and policy to address the many problems. View full abstract»

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  • TCP in wireless environments: problems and solutions

    Page(s): S27 - S32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (514 KB) |  | HTML iconHTML  

    The Internet provides a platform for rapid and timely information exchange among a disparate array of clients and servers. TCP and IP are separately designed and closely tied protocols that define the rules of communication between end hosts, and are the most commonly used protocol suite for data transfer in the Internet. The combination of TCP/IP dominates today's communication in various networks from the wired backbone to the heterogeneous network due to its remarkable simplicity and reliability, TCP has become the de facto standard used in most applications ranging from interactive sessions such as Telnet and HTTP, to bulk data transfer like FTP. TCP was originally designed primarily for wired networks. In a wired network, random bit error rate, a characteristic usually more pronounced in the wireless network, is negligible, and congestion is the main cause of packet loss. The emerging wireless applications, especially high-speed multimedia services and the advent of wireless IP communications carried by the Internet, call for calibration and sophisticated enhancement or modifications of this protocol suite for improved performance. Based on the assumption that packet losses are signals of network congestion, the additive increase multiplicative decrease congestion control of the standard TCP protocol reaches the steady state, which reflects the protocol's efficiency in terms of throughput and link utilization. However, this assumption does not hold when the end-to-end path also includes wireless links. Factors such as high BER, unstable channel characteristics, and user mobility may all contribute to packet losses. Many studies have shown that the unmodified standard TCP performs poorly in a wireless environment due to its inability to distinguish packet losses caused by network congestion from those attributed to transmission errors. In this article, following a brief introduction to TCP, we analyze the problems TCP exhibits in the wireless IP communication environment, and illustrate viable solutions by detailed examples. View full abstract»

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  • The new paradigm for wireless network optimization: a synergy of automated processes and human intervention

    Page(s): S14 - S21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6379 KB) |  | HTML iconHTML  

    With the evolution of wireless technologies, the optimization process for the radio access network has undergone a dramatic increase in complexity. This trend is driven by the introduction of multiple objectives for packet data services, the increasing network heterogeneity resulting from technology overlays, and the growing demand for nondisruptive optimization of operating networks. In a multidisciplinary effort, Bell Laboratories has developed a new optimization methodology that tackles these challenges using automated processes. We show that the paradigm shift toward automation requires the development of several interdependent algorithms each designed to cope with a particular optimization task. In the application described, human intervention proves indispensable; it demands a new kind of expertise that combines understanding of the automated processes with knowledge of network operation. Through examples we illustrate the variety of tasks that have to be automated and where guidance is needed through human control. The development of these automated processes is an important step toward dynamic optimization routines that are integrated into the network and adjust the network in a real-time manner. View full abstract»

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  • Design guidelines for routing protocols in ad hoc and sensor networks with a realistic physical layer

    Page(s): 101 - 106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB) |  | HTML iconHTML  

    We present guidelines on how to design network layer protocols when the unit disk graph (UDG) model is replaced by a more realistic physical layer model. Instead of merely using the transmission radius in the UDG model, physical, MAC, and network layers share the information about a bit and/or packet reception probability as a function of distance between nodes. We assume that all nodes use the same transmission power for sending messages, and that a packet is received when all its bits are correctly received. The MAC layer reacts to this probabilistic reception information by adjusting the number of acknowledgments and/or retransmissions. We observe that an optimal route discovery protocol cannot be based on a single retransmission by each node, because such a search may fail to reach the destination or find the optimal path. Next, we discuss that gaining neighbor knowledge information with "hello" packets is not a trivial protocol. We describe localized position-based routing protocols that aim to minimize the expected hop count (in case of hop-by-hop acknowledgments and fixed bit rate) or maximize the probability of delivery (when acknowledgments are not sent). We propose a guideline for the design of greedy position-based routing protocols with known destination locations. The node currently holding the message forwards it to a neighbor (closer to the destination than itself) that minimizes the ratio of cost over progress, where the cost measure depends on the assumptions and metrics used, while the progress measures the difference in distances to the destination. We consider two basic medium access layer approaches, with fixed and variable packet lengths. This article serves as a preliminary contribution toward the development of network layer protocols that match the assumptions and criteria already used in simulators and ultimately in real equipment. View full abstract»

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  • Mesh networks: commodity multihop ad hoc networks

    Page(s): 123 - 131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (585 KB) |  | HTML iconHTML  

    In spite of the massive efforts in researching and developing mobile ad hoc networks in the last decade, this type of network has not yet witnessed mass market deployment. The low commercial penetration of products based on ad hoc networking technology could be explained by noting that the ongoing research is mainly focused on implementing military or specialized civilian applications. On the other hand, users are interested in general-purpose applications where high bandwidth and open access to the Internet are consolidated and cheap commodities. To turn mobile ad hoc networks into a commodity, we should move to more pragmatic "opportunistic ad hoc networking" in which multihop ad hoc networks are not isolated self-configured networks, but rather emerge as a flexible and low-cost extension of wired infrastructure networks coexisting with them. Indeed, a new class of networks is emerging from this view: mesh networks. This article provides an overview of mesh networking technology. In particular, starting from commercial case studies we describe the core building blocks and distinct features on which wireless mesh networks should be based. We provide a survey of the current state of the art in off-the-shelf and proprietary solutions to build wireless mesh networks. Finally, we address the challenges of designing a high-performance, scalable, and cost-effective wireless mesh network. View full abstract»

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  • IEEE Communications Magazine

    Page(s): 0_1
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    Freely Available from IEEE
  • Table of contents

    Page(s): 2 - 3
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    Freely Available from IEEE
  • David newman named 2005 outstanding engineering alumnus at Pennsylvania State University

    Page(s): 8
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    Freely Available from IEEE
  • Conference calendar

    Page(s): 15 - 16
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    Freely Available from IEEE
  • CommuniCrostic puzzle

    Page(s): 18
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    Freely Available from IEEE

Aims & Scope

IEEE Communications Magazine covers all areas of communications such as lightwave telecommunications, high-speed data communications, personal communications systems (PCS), ISDN, and more.

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Editor-in-Chief
Sean Moore
Centripetal Networks