Showing papers in "IEEE Communications Magazine in 1999"

Light trees: optical multicasting for improved performance in wavelength routed networks

Abstract: We introduce the concept of a light-tree in a wavelength-routed optical network. A light-tree is a point-to-multipoint generalization of a lightpath. A lightpath is a point-to-point all-optical wavelength channel connecting a transmitter at a source node to a receiver at a destination node. Lightpath communication can significantly reduce the number of hops (or lightpaths) a packet has to traverse; and this reduction can, in turn, significantly improve the network's throughput. We extend the lightpath concept by incorporating an optical multicasting capability at the routing nodes in order to increase the logical connectivity of the network and further decrease its hop distance. We refer to such a point-to-multipoint extension as a light-tree. Light-trees can not only provide improved performance for unicast traffic, but they naturally can better support multicast traffic and broadcast traffic. In this study, we shall concentrate on the application and advantages of light-trees to unicast and broadcast traffic. We formulate the light-tree-based virtual topology design problem as an optimization problem with one of two possible objective functions: for a given traffic matrix, (i) minimize the network-wide average packet hop distance, or (ii) minimize the total number of transceivers in the network. We demonstrate that an optimum light-tree-based virtual topology has clear advantages over an optimum lightpath-based virtual topology with respect to the above two objectives.

New high-rate wireless LAN standards

Abstract: After the IEEE 802.11 standardization group established the first wireless LAN, several efforts were started to increase data rates and also to use other bands. This article describes the new wireless LAN standards developed by IEEE 802.11, ETSI BRAN, and MMAC. The new standards are targeting data rates up to 11 Mb/s in the 2.4 GHz band and up to 54 Mb/s in the 5 GHz band.

MPLS and traffic engineering in IP networks

Abstract: Rapid growth and increasing requirements for service quality, reliability, and efficiency have made traffic engineering an essential consideration in the design and operation of large public Internet backbone networks. Internet traffic engineering addresses the issue of performance optimization of operational networks. A paramount objective of Internet traffic engineering is to facilitate the transport of IP traffic through a given network in the most efficient, reliable, and expeditious manner possible. Historically, traffic engineering in the Internet has been hampered by the limited functional capabilities of conventional IP technologies. Recent developments in multiprotocol label switching (MPLS) and differentiated services have opened up new possibilities to address some of the limitations of the conventional technologies. This article discusses the applications of MPLS to traffic engineering in IP networks.

WASPNET: a wavelength switched packet network

Abstract: WASPNET is an EPSRC-funded collaboration between three British Universities: the University of Strathclyde, Essex University, and Bristol University, supported by a number of industrial institutions. The project which is investigating a novel packet-based optical WDM transport network-involves determining the management, systems, and devices ramifications of a new network control scheme, SCWP, which is flexible and simplifies optical hardware requirements. The principal objective of the project is to understand the advantages and potential of optical packet switching compared to the conventional electronic approach. Several schemes for packet header implementation are described, using subcarrier multiplexing, separate wave lengths, and serial transmission. A novel node design is introduced, based on wavelength router devices, which reduce loss, hence reducing booster amplifier gain and concomitant ASE noise. The fabrication of these devices, and also wavelength converters, are described. A photonic packet switching testbed is detailed which will allow the ideas developed within WASPNET to be tested in practice, permitting the practical problems of their implementation to be determined.

FPGA in the software radio

Abstract: As new radio standards are deployed without substantially supplanting existing ones, the need for multimode multiband handsets and infrastructure increases. This article describes how emerging FPGA technology's unique combination of size and power efficiency plus field programmability offers a transition of FPCAs from ASIC prototyping to embedded products. Software-defined receiver examples suggest an enlarged role for FPGAs in pragmatic paths toward the productization of software radio technology.

Resilience in multilayer networks

Abstract: The integration of different technologies such as ATM, SDH, and WDM in multilayer transport networks raises many questions regarding the coordination of the individual network layers. Especially in the area of network survivability, much can be gained by a better alignment of the healing actions taken by different network layers in case of outages. Survivability issues encountered in a multilayer environment include, among others: how to identify the original failure cause, how to appoint for each failure a layer responsible for its healing, how to let different layers interwork, and how to provide spare resources in an efficient way.

On multimedia networks: self-similar traffic and network performance

Abstract: The main objective in telecommunications network engineering is to have as many happy users as possible. In other words, the network engineer has to resolve the trade-off between capacity and QoS requirements. Accurate modeling of the offered traffic load is the first step in optimizing resource allocation algorithms such that provision of services complies with the QoS constraints while maintaining maximum capacity. As broadband multimedia services became popular, they necessitated new traffic models with self-similar characteristics. We present a survey of the self-similarity phenomenon observed in multimedia traffic and its implications on network performance. Our current research aims to fill the gap between this new traffic model and network engineering. An immediate consequence of this study is the demonstration of the limitations or validity of conventional resource allocation methods in the presence of self-similar traffic.

The 3GPP proposal for IMT-2000

Abstract: Market expectations for third-generation mobile radio systems (IMT-2000) show an increasing demand for a wide range of services from voice to low, high, and advanced data rate services to support mobile multimedia. This leads to technical requirements for IMT-2000 which are currently being standardized worldwide. Circuit- and packet-oriented services will be supported. These systems will operate in all radio environments to provide service to anyone, anytime, anywhere. The ITU has identified spectrum for the allocation of IMT-2000. However, these frequency bands are currently not available worldwide. In different regions research activities on IMT-2000 have been initiated to support the international consensus building process and standardization activities. Based on these activities system proposals have been submitted to ITU TG 8/1. In particular, the newly formed Third Generation Partnership Projects 3GPP and 3GPP2 have the objective of harmonizing similar proposals and defining detailed standards. Proposals from Europe, Japan, Korea, and the United States are very similar. The evolution and migration of second-generation systems to the third generation takes into account the deployed investment to save today's investment where useful and necessary. This article focuses on market and technical requirements and, in particular, the technical approach of 3GPP based on the big footprint of the GSM system.

Performance trends for analog to digital converters

Abstract: Analog-to-digital converters are key components of signal processing systems, and may even dictate system architectures due to their limitations on sampling rate and resolution. The state of the art for ADCs, including both experimental converters and commercially available parts, is reviewed. The data imply that the performance measure, P=2/sup SNRbits//spl middot/f/sub samp/, uncertainty in the sampling process (aperture jitter) over a very wide range of sampling rates. For ADCs operating at multi-GSPS rates, the speed of the device technology is also a limiting factor (due to comparator ambiguity). Technological progress as measured by P is discussed.

Recent advances in cellular wireless communications

Abstract: Testimonies of "wireless catching up with wireline" have begun. An information superhighway system is envisioned to fulfill the plethora of demand for wireless communications and the need for multimedia networks with multiservice requirements. The revolution in this technology will eventually free us, as communication users, from being tied down to a particular fixed location in a telephone network to person-to-person communications, via pocket-sized terminals, at an affordable price. This article briefly surveys the state of the art, standards, and technological growth experienced in mobile cellular (terrestrial and satellite) communications since the days of the ingenious inventions of Alexander Graham Bell and Guglielmo Marconi, over a century ago. Subsequently, we describe some emerging technological trends that can improve the capacity of third-generation systems and future outlooks for PCS networks in the next millennium.

Searching the Web: general and scientific information access

Abstract: The World Wide Web has revolutionized the way that people access information, and has opened up new possibilities in areas such as digital libraries, general and scientific information dissemination and retrieval, education, commerce, entertainment, government and health care. There are many avenues for improvement of the Web, for example in the areas of locating and organizing information. Current techniques for access to both general and scientific information on the Web provide much room for improvement, search engines do not provide comprehensive indices of the Web and have difficulty in accurately ranking the relevance of results. Scientific information on the Web is very disorganized. We discuss the effectiveness of Web search engines, including results that show that the major Web search engines cover only a fraction of the "publicly indexable Web". Current research into improved searching of the Web is discussed, including new techniques for ranking the relevance of results, and new techniques in metasearch that can improve the efficiency and effectiveness of Web search. The creation of digital libraries incorporating autonomous citation indexing is discussed for improved access to scientific information on the Web.

Very-high-speed digital subscriber lines

Abstract: VDSL services are overviewed with an emphasis on the basic architecture, applications, and data rates, as well as the technological challenges of design. Discussions of the telephone line environment, radio-band interference ingress and egress, impulse noise, and symmetric and asymmetric multiplexing are included, along with brief descriptions of two popular implementations.

Technical challenges in the globalization of software radio

Abstract: The software radio has emerged from the third-generation strategy for affordable, ubiquitous, global communications. This article reviews the concepts, architecture, technology challenges, and economics of the continuing productization and globalization of software radio.

Broadband RF stage architecture for software-defined radio in handheld terminal applications

Abstract: Broadband RF is a general-purpose common RF stage for every standard within a set of RF bands. The RF stage architecture presented in this article is suitable for software-defined radios. This article first defines the conceptual scheme of a handheld software defined radio (SDR) terminal, and then describes how the direct conversion principle is applied to the SDR. The discussion focuses on receiver hardware implementation and systematic control.

The origins of the sampling theorem

Abstract: The publications of Claude E. Shannon brought the sampling theorem to the broad attention of communication engineers. This article demonstrates how practicians, theoreticians, and mathematicians discovered the implications of the sampling theorem almost independent of one another.

Medium access control protocols performance in satellite communications

Abstract: Medium access control protocols are at the core of all forms of electronic communications systems. MAC protocols are designed to coordinate the transmission of packets, retransmission of damaged packets, and resolution of collisions among stations during a contention period. MAC protocols are foundations in low-level network architecture and play a significant role in the performance of higher-level protocols such as multiservices and multimedia application protocols. In this article five classes of MAC protocols are investigated with respect to their applications in satellite communications. These classes include fixed assignments, demand assignment, random access, hybrid random access and reservation, and adaptive protocols. Among several QoS objectives described in high-speed networking and the limitations inherent in satellite communications systems, in this article a set of important performance criteria are identified and used to evaluate different MAC protocols for satellite communications. The performance criteria include high channel throughput, low transmission delay, channel stability, protocol scalability, channel reconfigurability, broadband applicability, and low complexity of the control algorithm. For this, a simulation study is performed among selected MAC protocols from different classes, and their performances have been evaluated for NASA's Mars Regional Network.

MPLS advantages for traffic engineering

Abstract: This article discusses the architectural aspects of MPLS which enable it to address IP traffic management. Specific MPLS architectural features discussed are separation of control and forwarding, the label stack, multiple control planes, and integrated IP and constraint-based routing. The article then discusses how these features address network scalability, simplify network service integration, offer integrated recovery, and simplify network management. Scalability is addressed through integrated routing enabling a natural assignment of traffic to the appropriate traffic engineering tunnels without requiring special mechanisms for loop prevention. Change is greatly reduced. The label stack enables an effective means for local tunnel repair providing fast restoration. Feedback through the routing system permits fast and intelligent reaction to topology changes. Service integration is simplified through a unified QoS paradigm which makes it simple for services to request QoS and have it mapped through to traffic engineering.

Applying patterns to develop extensible ORB middleware

Abstract: Distributed object computing forms the basis for next-generation application middleware. At the heart of distributed object computing are object request brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. This article presents a case study of key patterns used to develop ORBs that can be dynamically configured and evolved for specific application requirements and network/end-system characteristics.

Dynamic channel reservation based on mobility in wireless ATM networks

Abstract: We present a dynamic channel reservation scheme to improve the utilization of wireless network resources while guaranteeing the required QoS of handoff calls. The wireless channels are dynamically reserved by using the request probability determined by the mobility characteristics and channel occupancy to guarantee acceptable quality of handoff calls and keep the new call blocking probability as low as possible.

Voice service interworking for PSTN and IP networks

Abstract: This article presents an overview of the main technical problems to be addressed for the provision of interoperable services between IP telephony and the PSTN. The pivotal element of the solution resides in an interworking function. This function is typically implemented in a gateway whose requirements and behavior are here analyzed in terms of signaling and control protocols (control plane) as well as user data transfer (user plane). The presentation is structured around these two planes. The control plane defines the set of signaling protocols to be used in each networking context and the translation between them. Detailed scenarios illustrate the signal translation in the gateway allowing for the establishment of a hybrid phone call. The user plane is responsible for adapting the user data to the properties of each network channel and determines the quality of service of the voice call in terms of delay and speech quality.

Synchronization with DMT modulation

Abstract: In a digital transmission system, synchronization is an essential receiver function. Accurate timing information must be known to the demodulator in order to produce reliable estimates of the transmitted data sequence. In this article, synchronization for discrete multitone transmission (DMT) is examined. The effect of imperfect timing on the receiver performance is investigated. An overview of timing estimation and correction circuits based on data-aided and non-data-aided algorithms derived from maximum-likelihood estimation theory is given.

All-optical WDM multi-rings with differentiated QoS

Abstract: This article considers all-optical WDM networks based on a slotted multichannel ring topology, where nodes are equipped with one fixed-wavelength receiver and one wavelength-tunable transmitter; and shows how to design very effective MAC protocols that provide packet-mode transport to multiple information flows with different QoS requirements. As an example, we describe SR3, a collision-free slotted MAC protocol which combines a packet scheduling strategy (called SRR), a fairness control algorithm (called MMR); and a reservation mechanism. SRR achieves an efficient exploitation of the available bandwidth, MMR guarantees fair throughput access to each node, and SR3, by permitting slot reservations, leads to tighter control on access delays, and can thus effectively support traffic classes with different QoS requirements.

Smart antennas for broadband wireless access networks

Abstract: This article is an overview of smart antenna applications in fixed broadband wireless access networks. Different smart antenna techniques are described including advances such as "spatial multiplexing" that can dramatically increase the performance of BWA networks. The impact of SA techniques on capacity and throughput of BWA networks is discussed.

Configurable logic for digital communications: some signal processing perspectives

Abstract: For the past two decades software programmable digital signal processors and ASICs have provided hardware solutions for signal processing system designers A new option has become available: field programmable gate arrays FPGA-based DSP platforms allow the designer to realize a data path that exactly matches the required processing, while at the same time maintaining the flexibility of a software approach This article presents an overview of some FPGA DSP applications Several filter designs are presented, and the use of CORDIC arithmetic for constructing an FPGA carrier recovery loop is outlined In addition to presenting design examples that can be realized using present-generation devices and tools, we take a brief look at how the dynamic reconfiguration aspect of certain FPGAs could be exploited in future-generation communication technologies

TCP/IP enhancements for satellite networks

Abstract: With the emerging market for high-mobility remote access broadband services, satellite networks are becoming increasingly popular. Although the ubiquitous TCP/IP protocol is widely used to provide reliable data delivery in terrestrial networks, it faces many challenges in satellite environments. These stem from the inherent features of satellite channels, such as large delays, increased error rates, and bandwidth asymmetry. To address these concerns, a variety of solutions have been proposed. These include direct TCP enhancements to better tune the TCP/IP stack and additional selective acknowledgment mechanisms. Other proposals use advanced interworking to reduce sensitivity to various channel features. Examples include multiple TCP sessions, link-layer interworking, and ACK control schemes. Improving onboard satellite features (buffer management, flow control) can also provide benefits for TCP/IP transport. The objective of this article is to present the various solutions and discuss their possible trade-offs. Overall, there exists a rich set of alternatives to meet the challenges in this important arena.

Reliable services in MPLS

Abstract: MPLS (multiprotocol label switching) is a convergence of various implementations of IP switching using ATM-like "label swapping" to speed up packet forwarding without changes to existing IP routing protocols. An important practical issue is the capability to recover quickly from faults. We examine distributed methods for fast fault recovery using modified label distribution protocol messages. To maintain and verify service continuity, methods are proposed for traffic and performance monitoring.

Optical multistage interconnection networks: new challenges and approaches

Abstract: Optical interconnections for communication networks and multiprocessor systems have been studied extensively. A basic element of optical switching networks is a directional coupler with two inputs and two outputs or switching elements (SEs). Depending on the control voltage applied to it, an input optical signal is coupled to either of the two outputs, setting the SE to either the straight or cross state. A class of topologies that can be used to construct optical networks is multistage interconnection networks, which interconnect their inputs and outputs via several stages of SEs. Although optical MINs hold great promise and have demonstrated advantages over their electronic counterparts, they also introduce new challenges such as how to deal with the unique problem of avoiding crosstalk in the SEs. In this article we survey the research carried out, including major challenges encountered and approaches taken, on optical MINs.

True number portability and advanced call screening in a SIP-based IP telephony system

Abstract: Custom local area signaling service features offered in the PSTN have certain limitations due to the closed nature of PSTN network signaling. The adoption of telephony over IP (IP telephony) will enable a new paradigm of services and features that are not possible to implement in today's PSTN. This is especially the case for services that make use of personal, trusted information, which can be provided by a user's personal digital assistant. We demonstrate how personal information can be coupled with an IP telephony service to provide user-customized call handling by the network. In particular, we describe a demonstration architecture that includes Ethernet-attached phones running SIP, with an interface to synchronize with PDAs that supply personal information. The proposed architecture is quite flexible; it can support enhanced versions of the current PSTN and private branch exchange services, in addition to many new features and services. We describe true number portability and advanced call screening as examples of new services in a hybrid PSTN/IP telephony environment.

Design issues of optical IP routers for Internet backbone applications

Abstract: The rapid increase of Internet traffic is pushing the deployment of WDM technology in the next-generation high-speed Internet backbone. Routers in the backbone could still be the potential bottleneck. In this article we consider some design issues of high-throughput optical routers which combine the advantages of WDM with the new optical switching technology. We first introduce a proposed Internet architecture based on the optical burst switching mechanism. Some important design issues in optical buffering and control function are addressed which are expected to have significant effects on router performance. Numerical results of a simulation study are also presented along with discussions.

The noise and crosstalk environment for ADSL and VDSL systems

Abstract: This article provides an overview of the noise and, in particular, the crosstalk environment in which DSL technology needs to operate. Transmission on the copper access network is subject to impairments which limit the achievable information capacity, and there is an urgent need to ensure that all DSL systems are spectrally compatible if the capacity of the network is to be fully realized. This article discusses the principles of frequency planning in copper access networks that help to ensure compatibility of deployed systems.