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Communications Magazine, IEEE

Issue 10 • Date Oct. 2003

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Displaying Results 1 - 16 of 16
  • Guest editorial - 50th anniversary of CLOS networks

    Page(s): 26 - 27
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    Freely Available from IEEE
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  • A survey of nonblocking multicast three-stage Clos networks

    Page(s): 34 - 37
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    The author gave a survey on multicast nonblocking multistage interconnection networks in his 1998 book. Here he focuses on the three-stage Clos network and its recursive extensions. Not only does this article bring the literature up to date, but it also provides some fresh viewpoints to either clarify or simplify some issues. View full abstract»

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  • Application and performance of downlink beamforming techniques in UMTS

    Page(s): 134 - 143
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    The opportunities and constraints for application of beamforming techniques in UMTS are reviewed and compared by means of extensive dynamic network-level simulations. We start by reviewing the physical layer specifications for UMTS in order to clarify which channels are allowed to use beamforming. Second, radio resource management for cells with beamforming capabilities are addressed from a standardization and algorithmic point of view. The exchange of beamforming specific measurement reports between the base station (Node-B) and the radio network controller is discussed as well as beam switching mechanisms, directional power-based admission control, and more. In addition to implementation of beamforming within logical cells, options for exploiting the antenna array to synthesize independent sector beams are also investigated (i.e., higher order sectorization via beamforming). The presented results show that beamforming within logical cells is an effective enabler for higher system capacity, while the use of beamforming for creation of many logical cells is less attractive due to significantly larger soft handover overhead and somewhat reduced capacity gain. View full abstract»

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  • Multirate Clos networks

    Page(s): 38 - 44
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    Clos networks are a class of multistage switching network topologies that provide alternate paths between inputs and outputs, making it possible to minimize or eliminate the blocking that can otherwise occur in such networks. In his seminal paper in the Bell System Technical Journal in 1953, Charles Clos showed how these networks could be configured to make them nonblocking and effectively launched the systematic study of switching system performance, a field that has developed a rich technical literature, and continues to be very active and of continuing practical importance. This article describes how Clos' results have been generalized to systems that support connections with varying bandwidth requirements. These generalizations have extended the application of Clos networks well beyond their original technological context and have led to a number of interesting new results, especially in connection with systems that support multicast communication. View full abstract»

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  • Multicarrier DS-CDMA: a multiple access scheme for ubiquitous broadband wireless communications

    Page(s): 116 - 124
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    We identify some of the key problems that may be encountered when designing a broadband multiple access system with bandwidth on the order of tens or even hundreds of megahertz. We commence with a comparative discussion in terms of the characteristics of three typical code-division multiple access schemes: single-carrier direct-sequence CDMA (SC DS-CDMA), multicarrier CDMA (MC-CDMA), and multicarrier DS-CDMA (MC DS-CDMA). Specifically, their benefits and deficiencies are analyzed when aiming to support ubiquitous communications over a variety of channels encountered in indoor, open rural, suburban, and urban environments. It is shown that when communicating in such diverse environments, both SC DS-CDMA and MC-CDMA exhibit certain limitations that are hard to circumvent. By contrast, when appropriately selecting the system parameters and using transmit diversity, MC DS-CDMA becomes capable of adapting to such diverse propagation environments at a reasonable detection complexity. View full abstract»

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  • QoS online routing and MPLS multilevel protection: a survey

    Page(s): 126 - 132
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    A survey of MPLS protection methods and their utilization in combination with online routing methods is presented in this article. Usually, fault management methods pre-establish backup paths to recover traffic after a failure. In addition, MPLS allows the creation of different backup types, and hence MPLS is a suitable method to support traffic-engineered networks. In this article, an introduction of several label switch path backup types and their pros and cons are pointed out. The creation of an LSP involves a routing phase, which should include QoS aspects. In a similar way, to achieve a reliable network the LSP backups must also be routed by a QoS routing method. When LSP creation requests arrive one by one (a dynamic network scenario), online routing methods are applied. The relationship between MPLS fault management and QoS online routing methods is unavoidable, in particular during the creation of LSP backups. Both aspects are discussed in this article. Several ideas on how these actual technologies could be applied together are presented and compared. View full abstract»

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  • Multicasting streaming media to mobile users

    Page(s): 81 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (765 KB) |  | HTML iconHTML  

    Content distribution in general, and multicasting in particular, over a wired network to static hosts can be realized by placing proxies and gateways at several parts of the network. However, if the end hosts are mobile over heterogeneous wireless access networks, one needs to consider many operational issues such as network detection, handoff, join and leave latency, and desired level of quality of service, as well as caching and load balancing. This article surveys a set of protocols and technologies that offer multicast-based services for streaming multimedia in a mobile environment. It also brings forth some of the issues related to mobile content distribution in the wireless Internet that may be helpful during its deployment by application service providers. View full abstract»

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  • Packet sequencing: a deterministic protocol for QoS in IP networks

    Page(s): 98 - 107
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    We describe a deterministic protocol for routing delay and loss-sensitive traffic through an IP network. Unlike traditional approaches, the method described here - packet sequencing - does not rely on queue management. Instead, it uses a temporally-based deterministic protocol to coordinate and switch IP packets on a systemwide basis. As a result, end-to-end throughput is guaranteed, without packet loss, loss variance, or accumulated performance impairment; additionally, end-to-end delay is minimized, and jitter is essentially eliminated. We also show that packet sequencing can complement conventional IP networks: sequencing does not negate the use of queue management QoS methods that are the subject of considerable ongoing study. This article describes the fundamental approach, issues associated with scalability, illustrative performance in the context of storage networking, and attributes related to the security and reliability of IP networks. View full abstract»

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  • Cross-layer design for wireless networks

    Page(s): 74 - 80
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    As the cellular and PCS world collides with wireless LANs and Internet-based packet data, new networking approaches will support the integration of voice and data on the composite infrastructure of cellular base stations and Ethernet-based wireless access points. This article highlights some of the past accomplishments and promising research avenues for an important topic in the creation of future wireless networks. We address the issue of cross-layer networking, where the physical and MAC layer knowledge of the wireless medium is shared with higher layers, in order to provide efficient methods of allocating network resources and applications over the Internet. In essence, future networks will need to provide "impedance matching" of the instantaneous radio channel conditions and capacity needs with the traffic and congestion conditions found over the packet-based world of the Internet. Furthermore, such matching will need to be coordinated with a wide range of particular applications and user expectations, making the topic of cross-layer networking increasingly important for the evolving wireless buildout. View full abstract»

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  • Multi-stage switching system using optical WDM grouped links based on dynamic bandwidth sharing

    Page(s): 56 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (633 KB) |  | HTML iconHTML  

    A three-stage Clos switch architecture is attractive because of its scalability. From an implementation point of view, it allows us to relax the cooling limitation, but there is a problem interconnecting different stages. This article presents a three-stage switching system that uses optical WDM grouped links and dynamic bandwidth sharing. We call it a WDM grouped-link switch. The introduction of WDM makes the number of cables used in the system proportional to the switch size. Dynamic bandwidth sharing among WDM grouped links prevents the statistical multiplexing gain offered by WDM from falling even if the switching system becomes large. The WDM grouped-link switch uses cell-by-cell wavelength routing. A performance evaluation confirms the scalability and cost-effectiveness of this switch. An implementation of the WDM grouped link and a compact planar lightwave circuit platform is described. This architecture allows us to expand the throughput of the switching system up to 5 Tb/s. View full abstract»

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  • A perspective on the evolution of mobile communications

    Page(s): 66 - 73
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    This article outlines the current state of mobile communications and presents some of the future directions in research and development from the perspective of NTT DoCoMo with special emphasis on the market in Japan. It first describes the directions in which mobile communications are expected to forge ahead in the future, and the service implementation strategies they could employ. Then it describes an example of mobile multimedia services and present an outline of the Freedom of Mobile Multimedia Access (FOMA), which is a service based on the 3G mobile communications system called International Mobile Telecommunications-2000 (IMT2000). This is followed by an overview of our R&D approach to 4G systems, which constitute mobile communications systems of the future, and the profile of technologies to make these happen. Finally, it reviews our approach to future technologies that are expected to be realized in 4G and subsequent systems, and illustrate it with an example of a research project. View full abstract»

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  • On the future of Internet management technologies

    Page(s): 90 - 97
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    As the Internet continues to grow, it becomes more and more apparent that existing Internet management technologies need to be improved, extended or replaced in order to extend functionality and reduce development time and operational costs. Within the IETF, IRTF, and IAB, several new approaches are currently under discussion. Evolutionary approaches aim at improving currently used technologies, whereas revolutionary approaches try to replace existing management-specific technologies with standard distributed systems technologies. This article surveys the research and development work under way to develop future Internet management technologies. View full abstract»

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  • Nonblocking, repackable, and rearrangeable Clos networks: fifty years of the theory evolution

    Page(s): 28 - 33
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    The article gives an overview of major theoretical issues associated with a switching network structure proposed by C. Clos (1953). The concepts of strict-sense and wide-sense nonblocking as well as repackable and rearrangeable networks are described, showing the development of major research areas. A taxonomy of Clos switching networks and some important results for the basic network structure are given and discussed. Other research issues are enumerated. View full abstract»

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  • Hybrid TDMA/CDMA based on filtered multitone modulation for uplink transmission in HFC networks

    Page(s): 108 - 115
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    We present a hybrid TDMA/CDMA system for uplink transmission in multiple access networks that is based on filtered multitone modulation. We consider an application to uplink transmission in hybrid fiber/coax networks. After discussing the characteristics of the proposed system, we address the problem of initial ranging and power adjustment of unregistered stations. Finally, we introduce a new collision resolution algorithm in conjunction with FMT modulation that uses iterative identification of the competing stations to achieve high throughput on the collision channel. System performance is investigated by simulations. View full abstract»

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  • Matching algorithms for three-stage bufferless Clos network switches

    Page(s): 46 - 54
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    Three-stage Clos network switches are an attractive solution for future broadband packet routers due to their modularity and scalability. Most three-stage Clos network switches assume either all modules are space switches without memory (bufferless), or employ shared memory modules in the first and third stages (buffered). The former is also referred to as the space-space-space (S3) Clos network switch, while the latter is referred to as the memory-space-memory (MSM) Clos network switch. We provide a survey of recent literature concerning switching schemes in the S3 Clos network switch. The switching problem in the S3 Clos network switch can be divided into two major parts, namely port-to-port matching (scheduling) and route assignment between the first and third stages. Traditionally, researchers have proposed algorithms to solve these issues separately. Recently, a new class of switching algorithms, called matching algorithms for Clos (MAC), has been proposed to solve scheduling and route assignment simultaneously. We focus on the MAC schemes and show that the new class of algorithms can achieve high performance and maintain good scalability. View full abstract»

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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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Meet Our Editors

Editor-in-Chief
Sean Moore
Centripetal Networks