Showing papers in "IEEE Communications Magazine in 1994"

Kerberos: an authentication service for computer networks

Abstract: When using authentication based on cryptography, an attacker listening to the network gains no information that would enable it to falsely claim another's identity. Kerberos is the most commonly used example of this type of authentication technology. The authors concentrate on authentication for real-time, interactive services that are offered on computer networks. They use the term real-time loosely to mean that a client process is waiting for a response to a query or command so that it can display the results to the user, or otherwise continue performing its intended function. This class of services includes remote login, file system reads and writes, and information retrieval for applications like Mosaic. >

Access control: principle and practice

Abstract: Access control constrains what a user can do directly, as well as what programs executing on behalf of the users are allowed to do. In this way access control seeks to prevent activity that could lead to a breach of security. This article explains access control and its relationship to other security services such as authentication, auditing, and administration. It then reviews the access matrix model and describes different approaches to implementing the access matrix in practical systems, and follows with a discussion of access control policies commonly found in current systems, and a brief consideration of access control administration. >

Traffic modeling for telecommunications networks

Abstract: As new communications services evolve, professionals must create better models to predict system performance. The article provides an overview of computer simulation modelling for communication networks, as well as some important related modelling issues. It gives an overview of discrete event simulation and singles out two important modelling issues that are germane to extant and emerging networks: traffic modelling and rare event simulation. Monte Carlo computer simulation is used as a performance prediction tool and Markov models are considered. >

Network firewalls

Abstract: Computer security is a hard problem. Security on networked computers is much harder. Firewalls (barriers between two networks), when used properly, can provide a significant increase in computer security. The authors classify firewalls into three main categories: packet filtering, circuit gateways, and application gateways. Commonly, more than one of these is used at the same time. Their examples and discussion relate to UNIX systems and programs. The majority of multiuser machines on the Internet run some version of the UNIX operating system. Most application-level gateways are implemented in UNIX. This is not to say that other operating systems are more secure; however, there are fewer of them on the Internet, and they are less popular as targets for that reason. But the principles and philosophy apply to network gateways built on other operating systems as well. Their focus is on the TCP/IP protocol suite, especially as used on the Internet. >

Simulation of communication systems

Abstract: When both a complex system and a complex channel model are encountered, the result is typically a design or analysis problem that cannot be solved using traditional (pencil and paper) mathematical analysis. Computer-aided techniques, which usually involve some level of numerical simulation, can be a very valuable tool in these situations. The purpose of this article is to provide a tutorial review of some of the basic techniques of communication system simulation. The authors consider the basic techniques used to represent signals, generate signals, and model linear systems, nonlinear systems, and time-varying systems within a simulation. They consider the important problem of using a simulation to estimate the performance of a communication system. >

An open-systems approach to video on demand

Abstract: Open systems will enable video servers and set-tops to provide different services in a variety of environments Hewlett-Packard is interested in applying the principles of open systems to video on demand (VOD) In particular, the company is developing a technology base that will allow their servers and set-tops to operate in a variety of environments and enable the provision of a variety of services The impact that the different VOD system elements have on the video server and set-top are examined from a communications standpoint Opportunities for open or standard interfaces are identified and recommendations are made on what these should be where possible >

MPEG coding for variable bit rate video transmission

Abstract: For real-time transmission of broadcast-quality video on ATM-based B-ISDN, the intraframe to interframe ratio and the quantizer scale are two key parameters that can be used to control a video source in a network environment Their impact on the traffic characteristics of the coder provides insights into the cell arrival process for an MPEG source The authors obtain video source models for coders that utilize a standard algorithm that can be applied to a multitude of video services The output stream of a video coder, which complies with the Motion Pictures Expert Group (MPEG) coding standard, is studied with an National Television Systems Committee (NTSC) quality video sequence as the input Because the MPEG video coding algorithm has been proposed for a variety of applications, they also investigate the effect of changing the coding parameters on the statistics of interest >

Interactive video on demand

Abstract: Video on demand (VOD)/spl minus/likely to become one of the most successful services in the emerging broadband network/spl minus/must minimize bandwidth requirements to serve large numbers of users. This article describes two VOD service variants, whereby bandwidth requirements in the network are reduced, while keeping the quality of service (QoS) at an equally high level. >

Traffic management for ATM local area networks

Abstract: Asynchronous transfer mode (ATM) is the first switching technology to be capable of supporting circuit switching and packet switching within a single integrated switching mechanism. This was one of the research goals that led to the development of ATM. Considerable progress has already been made in implementing constant bit-rate services, similar to conventional circuit switching, over ATM. The authors briefly consider how to support LAN emulation over an ATM network and then explore how to offer the dynamic bandwidth sharing in the local area. Considerable progress has already been made in implementing constant bit-rate services, similar to conventional circuit switching, over ATM. However, the bursty nature of data traffic requires dynamic bandwidth sharing similar to packet switching, and this is still under investigation. >

Inverse multiplexing

Abstract: Inverse multiplexing offers an approach to high-speed data networking that is different than many other currently fashionable network technologies. It uses a new type of customer premises-based equipment that makes use of existing network services to provide significantly enhanced functionality, rather than requiring a new and yet-to-be-implemented set of capabilities to be added to the network. This puts more control into users' hands. Inverse multiplexers provide the ability to dial up multimegabit-per-second digital connections without requiring significant changes to the network itself. It is this ability to use currently available network offerings in a new and highly useful manner that makes inverse multiplexing such a valuable addition to the corporate networking toolbox. >

Optical time division multiplexing: systems and networks

Abstract: The recent advances in optical time division multiplexed (OTDM) systems and components research show the technique to be highly suited to the generation and transmission of high capacity data on a single optical carrier. This approach uses a single wavelength to carry capacities of at least 40 Gb/s. Such systems are based on a clock frequency and tributary data rates which are easily accessible using electronic components. Short optical pulses are used in a return-to-zero data transmission format with temporal interleaving to map a number of optical data channels into a single electronic clock cycle. It is an approach that can be used to achieve extremely high data-rate bit interleaved systems. This article summarizes the developments in this field and outlines a possible methodology to evolve transport networks to encompass the potential that both WDM and OTDM have to offer. >

ATM local area networks

Abstract: LAN emulation offers a best-effort, connectionless, packet transfer service at the MAC sublayer, implemented on top of a connection-oriented ATM network LAN emulation using switched virtual connections requires address resolution to locate the destination end station followed by connection establishment to the resulting ATM address. Address resolution may be implemented by a broadcast technique or by an address server. The broadcast method is the simplest for small networks but a combination of both is probably better. The use of the MAC address to identify an end station, with dynamic binding to its current physical location in the ATM network, allows the ATM LAN segment to be viewed as a virtual LAN. The virtual LAN model permits end stations to move and change physical location while maintaining connection to the same ATM LAN segment. This greatly simplifies the management of large data networks. >

Hierarchical coding of digital television

Abstract: If the same digital television signal is used for multiple resolutions, bit rates, or transmission and storage mechanisms, then hierarchical coding offers several advantages. The FCC has decided to adopt the "main profile" of MPEG-2 for the video representation of the signal that will be used in the North American terrestrial broadcasting of HDTV. The article examines the tradeoffs of using hierarchical coding and provides an overview of possible applications and existing techniques, with emphasis on the scaleable profiles of MPEG-2, in particular the technique of spatial domain scalability. >

Simulation software for communications networks: the state of the art

Abstract: In the last five to ten years, simulation has been used with greater frequency to analyze communications networks, due in part to the increased number of networks in existence and to their greater complexity. The authors define the types of simulation software that are available for network analyses and also discuss desirable features for such products. They then present brief descriptions of seven prominent simulation products, emphasizing their approach to building a simulation model. They also give a four-activity approach for selecting a simulation package for an organization or a particular application. A general reference for the simulation concepts discussed in this article is Law and Kelton (1991). >

Applicability of ADSL to support video dial tone in the copper loop

Abstract: An ADSL-3 architecture providing a downstream payload above 6 Mb/s has been proposed for operation over carrier serving area (CSA) loops. To determine whether such a system can be reliably deployed in the telephone company copper loop plant, a detailed model for loops and noise is presented. Results show that a sophisticated system, including echo cancellation and trellis coding, can reliably achieve CSA coverage, if T1 is not present in the plant. In the presence of assumed T1 worst case conditions, either the downstream bit rate must be reduced, or the operating range needs to be decreased to a serving area smaller than the CSA. A smaller "mid-CSA" serving area is proposed, and it is demonstrated that a 6.3-Mb/s ADSL (asymmetric digital subscriber line) system can operate in the presence of T1 in adjacent binder groups over this smaller serving area, which is roughly defined by 6 kilofeet of 26 gauge and 8 kilofeet of 24 gauge. A statistical study utilizing actual T1 line data suggests that if CSA coverage is attempted in the presence of T1 in adjacent binder groups, a success rate of greater than 92 percent can be expected. >

Toward a national public key infrastructure

Abstract: Reliance on electronic communications makes information more vulnerable, and users will require confidentiality, message integrity, sender authentication, and sender non-repudiation. Public key cryptography will play an important role in providing these services. >

The past, present, and future of inverse multiplexing

Abstract: Inverse multiplexing refers to the process of aggregating channels to allow applications greater freedom in selecting the optimum communication bandwidth and cost. The history of the Bandwidth On Demand Interoperability Group (BONDING) standard and its relationship to current and emerging network architectures are discussed. Applications of bandwidth-on-demand products to videoconferencing, multimedia, and LAN interconnection are described with respect to current and future equipment capabilities. Many data transmission applications require transmission at bit rates higher than those available from carriers. Services are most cost effectively provided if they have characteristics common among many user applications. The present paper describes an increasingly popular solution to this problem given today's expanding switched digital networks. Referred to as "inverse multiplexers" current implementations are providing national and international connectivity for diverse applications involving high-quality videoconferencing, variable-demand LAN interconnections, and low-cost network backup. >

Key escrowing today

Abstract: The objective of the US Government's Escrowed Encryption Standard (EES) and associated Key Escrow System (KES) is to provide strong security for communications while simultaneously allowing authorized government access to particular communications for law enforcement and national security purposes. The article describes the EES and the KES. Particular emphasis is given to security, since potential users have been concerned that the hooks which provide authorized government access could be exploited or abused. It describes many of the safeguards that have gone into the design of the KES in order to ensure that the risk of unauthorized access to EES-encrypted communications is negligible. >

Simulation issues for future wireless modems

Abstract: Mobile communication systems present several design challenges that stem from the mobility of users throughout the system and the time-varying multipath channel and interference. To address these challenges, future wireless modems will rely on performance enhancing techniques such as adaptive antennas, DSP-based interference rejection techniques, and real-time signal processing for capacity improvement. The authors present an overview of key simulation issues for wireless communications systems. First, the burst error characteristics of the mobile channel require the selection of appropriate performance measures. Second, accurate simulations require realistic channel models that include the effects of attenuation, multipath propagation, noise, and interference. Third, link-level simulation of wireless systems requires attention to details of system implementation including the effects of nonlinearities. Finally, efficient simulation of CDMA systems may require a combination of analytic and simulation techniques. >

Baseband and passband transport systems for interactive video services

Abstract: As essentially none of the existing telecommunication networks are capable of providing interactive video services (IVS), network providers have begun to consider the network architecture that is best to deploy. Two approaches have received most of the consideration. Because of the embedded base of broadcast, coax-based cable TV networks and because of the unconfirmed demand for IVS, much attention has been paid to upgrading these networks to provide IVS transport even though extensive modification would be required. These networks are referred to as passband networks because of the use of modulated subcarriers as the signal transport mechanism. The alternative approach under consideration is the use of fiber-to-the-curb transport systems. Because such networks transport IVS directly as baseband signals without subcarrier modulation, they are known as baseband networks. The paper compares the baseband and passband approaches in several areas including: compatibility with the optical transmission medium; compatibility with IVS source/sink equipment; compatibility with the emerging telecommunications interoffice and feeder networks; and the cost of deployment. The recent history in which passband and baseband approaches competed to become the preferred transport mechanism in LAN applications is reviewed. The fact that in that case baseband emerged as the preferred approach has important implications for the selection of the preferred approach in today's IVS applications. The constituent elements and transport requirements of the end-to-end network for delivering IVS are reviewed. >

Digital television terrestrial broadcasting

Abstract: Digital transmission will change the way television channels are allocated and will force broadcasters to master a new set of parameters for optimizing service coverage. This article discusses modulation and channel coding issues related to digital television terrestrial broadcasting (DTTB), such as data throughput, spectrum efficiency, single- and multicarrier modulations, interferences under simulcasting conditions, multilayer services, and DTTB coverage. Current advanced television (ATV) research for terrestrial broadcasting in the VHF/UHF bands is converging toward a fully digital implementation. In a digital ATV system, the digitized high definition video sources, with raw bit rate of up to l-Gb/s, are compressed using source coding techniques based on the discrete cosine transform (DCT) coding. The output data rate of the video source encoder, with present technology, is typically 15 to 20 Mb/s. This data rate is sufficient to provide a satisfactory distribution quality video service. >

The scalable lightwave network

Abstract: In principle, an optical network employing wavelength routing, wavelength reuse, and multihop packet switching is modularly scalable to very large configurations in both the hardware and software sense. As such, it is a viable architecture for a new ATM-based telecommunications infrastructure The network architecture considered for a new, scalable, broadband telecommunications infrastructure is based on (1) the use of wavelength division multiplexing (WDM) and wavelength routing; (2) the translation of signals from one wavelength to another at the access stations; and (3) the use of multihop ATM packet switching. These principles permit networks to be built whose size is essentially unlimited. >

Data communications using ATM: architectures, protocols, and resource management

Abstract: The introduction of ATM is being propelled by the need for fast data communications in public and private networks. What is needed is a clear picture of protocol architectures and traffic characteristics of the various applications to be supported both now and in the future. The authors discuss ATM network architectures with special focus on the support of connectionless LAN interconnection and show which benefits can be obtained from the introduction of a connectionless server in an ATM network. They outline issues related to the use of existing protocols when ATM networks are introduced and show which protocol complexities have to be handled by gateways and servers, again using the example of connectionless LAN interconnection. Having presented network and protocol architectures the issue of data communication in ATM, resource allocation, is treated. >

Network planning for third-generation mobile radio systems

Abstract: The success of UMTS relies not only on the development of a flexible air interface, efficient coding techniques, and handset technology; it is equally important to design a system that can support the underlying technology and to interface with other networks. >

Connectionless service for public ATM networks

Abstract: The interconnection of connectionless LANs and MANs over a connection-oriented B-ISDN presents a dilemma with regard to efficient interoperability. In order to provide solutions to this dilemma, there have been many techniques proposed. We describe and evaluate the architectural and conceptual alternatives available for the implementation of a connectionless service for public ATM networks. We also suggest a scheme through which best-effort connectionless service may be provided in public ATM networks using connectionless servers and hop-by-hop flow control. There is as yet no consensus on issues such as bandwidth management, address resolution, connectionless server forwarding modes, or connectionless server topology, and therefore much of the area remains open for research. These research issues must be addressed, however, in order to realize the interoperability, and thereby the acceptance, of ATM. >

IP on ATM local area networks

Abstract: ATM offers increased bandwidth and greater flexibility and manageability. However, ATM's success as a LAN technology depends on its ability to provide LAN-like services compatible with existing protocols and applications. The authors address the various issues in the design and implementation of the Internet Protocol (IP) in the evolving ATM LANs. >

Rural communications in India using fixed cellular radio systems

Abstract: Seventy-five percent of India's population is in rural villages, yet almost 90 percent of the country's phones are in urban sites. The authors propose a fixed cellular radio system, combined with the existing mobile network, as a cost effective way to extend telecommunications services to India's rural areas. >

Optical local area network technologies

Abstract: To utilize the large bandwidth of optical fiber, optical LANs must employ architectures that fundamentally differ from current single-channel LAN architectures. With computer processor speeds continuing to grow exponentially and multimedia applications growing even faster, there is a strong need for higher-speed local area networks (LANs) that can handle the traffic generated by tomorrow's LAN users. Optical fiber is well suited for high-speed traffic transport, but the busty nature of computer traffic and large number of users makes it difficult to utilize the fiber's capacity in LANs. The incorporation of multiple payload channels in future LANs is seen as a necessity; WDM is a good candidate for achieving this. The rapidly improving optical component technologies allow more flexible WDM architecture designs for various emerging applications. >

Soliton transmission in telecommunication networks

Abstract: Erbium-doped fiber amplifiers are a major breakthrough for soliton communication. Most of the difficult problems preventing soliton communication recently were solved using erbium-doped optical fiber amplifiers (EDFAs). Progress in optical soliton communication has been very rapid, since the invention of the 1.48 /spl mu/m laser diode pumped EDFA, mainly because of its great potential for high-speed communication. This article describes how optical soliton communication has been established, together with the recently developed "soliton control" technique. >

Wireless LANs: physical properties of infra-red systems vs. mmw systems

Abstract: Interest in wireless indoor communications has been spectacular. As we tend to need relatively broad bandwidths for such communication, the choice of carrier frequency would seem to be between the millimeter-wave/upper microwave bands and infra-red. The authors consider those systems which operate with one cell or multiple cells within a room. Such systems in the longer term must offer speeds compatible with fiber distributed data interface (FDDI) or the integrated broadband communications network (IBCN). Keeping this in mind, the authors look at the capability of systems supporting transmission rates of 100 Mb/s, though of course useful networks can be realized with much lower single user data transfer rates. As with mmw, infrared (IR) radiation is essentially restricted to the room in which it is generated; apart from leakage through windows and doors it will not normally be detected outside a room and should not interfere significantly with similar systems in neighboring offices. However, IR is not suitable for operation in very large rooms. In addition it is seen that mmw offers certain advantages in both large and small rooms. >