Electronics & Communication Engineering Journal
Volume 8, Issue 4, August 1996
Volumes & issues:
Volume 8, Issue 4
August 1996
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- Source: Electronics & Communication Engineering Journal, Volume 8, Issue 4, p. 154 –155
- DOI: 10.1049/ecej:19960406
- Type: Article
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- Author(s): M. Fontaine and D.G. Smith
- Source: Electronics & Communication Engineering Journal, Volume 8, Issue 4, p. 156 –164
- DOI: 10.1049/ecej:19960401
- Type: Article
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156
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Asynchronous transfer mode (ATM) is the transmission format for almost all future communication networks, including broadband integrated services digital networks (B-ISDN). The key feature of ATM is its high flexibility in bandwidth allocation. Instead of reserving capacity for each connection, the bandwidth is allocated on demand. As a consequence, packets (called cells in ATM terminology) might be lost. To guarantee a given quality of service (QoS), some kind of control is needed to decide whether to accept or to reject an incoming connection. A connection is accepted only if the network has sufficient resources to achieve the QoS required by the user without affecting the QoS of the existing connections. In ATM networks, connection admission control (CAC) is responsible for this decision. It is a very complex function because the traffic may vary greatly and have poorly known characteristics. This paper describes CAC procedures proposed in the literature and discusses issues related to bandwidth allocation in ATM networks. It shows that CAC and statistical multiplexing are only needed for certain connections. - Author(s): D.J. Daniels
- Source: Electronics & Communication Engineering Journal, Volume 8, Issue 4, p. 165 –182
- DOI: 10.1049/ecej:19960402
- Type: Article
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165
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Surface-penetrating radar is a nondestructive testing technique which uses electromagnetic waves to investigate the composition of nonconducting materials either when searching for buried objects or when measuring their internal structure. A typical surface-penetrating radar transmits a short pulse of electromagnetic energy of 1 ns (10-9 s) time duration from a transmit antenna into the material. Energy reflected from discontinuities in impedance is received by means of a receive antenna and is then suitably processed and displayed by a radar receiver and display unit. If the transmit and receive antennas are moved at a constant velocity along a linear path, a cross-sectional image of the material can be generated. Alternatively, if the antennas are scanned in a regular grid pattern, a three-dimensional image of the target can be derived. This paper provides a review of the principles of the technique, discusses the technical requirements for the individual subsystems comprising a surface-penetrating radar and provides examples of typical applications for the method. Continued technical improvements in system performance enable clearer radar images of the internal structure of materials to be obtained, thus advancing the application of the technique. - Author(s): P. Duggan
- Source: Electronics & Communication Engineering Journal, Volume 8, Issue 4, p. 183 –190
- DOI: 10.1049/ecej:19960403
- Type: Article
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183
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Security measures are being applied in the Telecom Eireann trunk telephone network to minimise disruption due to excess traffic or system failure. Dynamic measures, such as network management, will be deployed in the very near future, but in the meantime static measures are being applied. Geographically separate exchanges of the same status are provided at major nodes with traffic shared equally between them on separate transmission links. Rerouting is provided automatically when a system fails, but at a reduced grade of service. The paper presents a model which simulates this concept of mutual alternative routing using the UNIX-based OPNET (Optimised Network Engineering Tools) package. - Author(s): C. Ward ; M. Smith ; A. Jeffries ; D. Adams ; J. Hudson
- Source: Electronics & Communication Engineering Journal, Volume 8, Issue 4, p. 191 –200
- DOI: 10.1049/ecej:19960404
- Type: Article
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Cellular communications have become the success story of the late 20th century. In just 15 years the global cellular subscriber base has grown to 60 million and it is forecast to exceed 350 million by early next century. This rapid growth has created the dichotomy for cellular operators of increasing pressure from customers to improve coverage, capacity and quality within their networks whilst the ever growing competition in the cellular marketplace demands that operational costs be reduced to the lowest possible level. One development which can assist network operators in reconciling these conflicting demands is the smart antenna. However, the successful deployment of smart antennas will require a much greater understanding of the characteristics of signals within the mobile/base-station transmission path. The measurement equipment described in this paper has enabled the acquisition of data which contributes significantly towards the understanding of these propagation path characteristics.
Radio access: your flexible friend
Bandwidth allocation and connection admission control in ATM networks
Surface-penetrating radar
A mutual alternative routing model for circuit-switched networks
Characterising the radio propagation channel for smart antenna systems
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