33 research outputs found
Quality aspects of Internet telephony
Internet telephony has had a tremendous impact on how people communicate.
Many now maintain contact using some form of Internet telephony.
Therefore the motivation for this work has been to address the quality aspects
of real-world Internet telephony for both fixed and wireless telecommunication.
The focus has been on the quality aspects of voice communication,
since poor quality leads often to user dissatisfaction. The scope of the work
has been broad in order to address the main factors within IP-based voice
communication.
The first four chapters of this dissertation constitute the background
material. The first chapter outlines where Internet telephony is deployed
today. It also motivates the topics and techniques used in this research.
The second chapter provides the background on Internet telephony including
signalling, speech coding and voice Internetworking. The third chapter
focuses solely on quality measures for packetised voice systems and finally
the fourth chapter is devoted to the history of voice research.
The appendix of this dissertation constitutes the research contributions.
It includes an examination of the access network, focusing on how calls are
multiplexed in wired and wireless systems. Subsequently in the wireless
case, we consider how to handover calls from 802.11 networks to the cellular
infrastructure. We then consider the Internet backbone where most of our
work is devoted to measurements specifically for Internet telephony. The
applications of these measurements have been estimating telephony arrival
processes, measuring call quality, and quantifying the trend in Internet telephony
quality over several years. We also consider the end systems, since
they are responsible for reconstructing a voice stream given loss and delay
constraints. Finally we estimate voice quality using the ITU proposal PESQ
and the packet loss process.
The main contribution of this work is a systematic examination of Internet
telephony. We describe several methods to enable adaptable solutions
for maintaining consistent voice quality. We have also found that relatively
small technical changes can lead to substantial user quality improvements.
A second contribution of this work is a suite of software tools designed to
ascertain voice quality in IP networks. Some of these tools are in use within
commercial systems today
Telecommunications Networks
This book guides readers through the basics of rapidly emerging networks to more advanced concepts and future expectations of Telecommunications Networks. It identifies and examines the most pressing research issues in Telecommunications and it contains chapters written by leading researchers, academics and industry professionals. Telecommunications Networks - Current Status and Future Trends covers surveys of recent publications that investigate key areas of interest such as: IMS, eTOM, 3G/4G, optimization problems, modeling, simulation, quality of service, etc. This book, that is suitable for both PhD and master students, is organized into six sections: New Generation Networks, Quality of Services, Sensor Networks, Telecommunications, Traffic Engineering and Routing
Operational Research: Methods and Applications
Throughout its history, Operational Research has evolved to include a variety of methods, models and algorithms that have been applied to a diverse and wide range of contexts. This encyclopedic article consists of two main sections: methods and applications. The first aims to summarise the up-to-date knowledge and provide an overview of the state-of-the-art methods and key developments in the various subdomains of the field. The second offers a wide-ranging list of areas where Operational Research has been applied. The article is meant to be read in a nonlinear fashion. It should be used as a point of reference or first-port-of-call for a diverse pool of readers: academics, researchers, students, and practitioners. The entries within the methods and applications sections are presented in alphabetical order. The authors dedicate this paper to the 2023 Turkey/Syria earthquake victims. We sincerely hope that advances in OR will play a role towards minimising the pain and suffering caused by this and future catastrophes
AN INVESTIGATION INTO AN EXPERT SYSTEM FOR TELECOMMUNICATION NETWORK DESIGN
Many telephone companies, especially in Eastern-Europe and the 'third world', are
developing new telephone networks. In such situations the network design engineer needs
computer based tools that not only supplement his own knowledge but also help him to cope
with situations where not all the information necessary for the design is available. Often
traditional network design tools are somewhat removed from the practical world for which
they were developed. They often ignore the significant uncertain and statistical nature of the
input data. They use data taken from a fixed point in time to solve a time variable problem,
and the cost formulae tend to be on an average per line or port rather than the specific case.
Indeed, data is often not available or just plainly unreliable. The engineer has to rely on
rules of thumb honed over many years of experience in designing networks and be able to
cope with missing data.
The complexity of telecommunication networks and the rarity of specialists in this area often
makes the network design process very difficult for a company. It is therefore an important
area for the application of expert systems. Designs resulting from the use of expert systems
will have a measure of uncertainty in their solution and adequate account must be made of
the risk involved in implementing its design recommendations.
The thesis reviews the status of expert systems as used for telecommunication network
design. It further shows that such an expert system needs to reduce a large network problem
into its component parts, use different modules to solve them and then combine these results
to create a total solution. It shows how the various sub-division problems are integrated to
solve the general network design problem. This thesis further presents details of such an
expert system and the databases necessary for network design: three new algorithms are
invented for traffic analysis, node locations and network design and these produce results
that have close correlation with designs taken from BT Consultancy archives.
It was initially supposed that an efficient combination of existing techniques for dealing with uncertainty
within expert systems would suffice for the basis of the new system. It soon
became apparent, however, that to allow for the differing attributes of facts, rules and data
and the varying degrees of importance or rank within each area, a new and radically different
method would be needed.
Having investigated the existing uncertainty problem it is believed that a new more rational
method has been found. The work has involved the invention of the 'Uncertainty Window'
technique and its testing on various aspects of network design, including demand forecast,
network dimensioning, node and link system sizing, etc. using a selection of networks that
have been designed by BT Consultancy staff. From the results of the analysis, modifications
to the technique have been incorporated with the aim of optimising the heuristics and
procedures, so that the structure gives an accurate solution as early as possible.
The essence of the process is one of associating the uncertainty windows with their relevant
rules, data and facts, which results in providing the network designer with an insight into the
uncertainties that have helped produce the overall system design: it indicates which sources
of uncertainty and which assumptions are were critical for further investigation to improve
upon the confidence of the overall design. The windowing technique works by virtue of its
ability to retain the composition of the uncertainty and its associated values, assumption, etc.
and allows for better solutions to be attained.BRITISH TELECOMMUNICATIONS PL
Proceedings of the Fifth International Mobile Satellite Conference 1997
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments
Operational Research: Methods and Applications
Throughout its history, Operational Research has evolved to include a variety of methods, models and algorithms that have been applied to a diverse and wide range of contexts. This encyclopedic article consists of two main sections: methods and applications. The first aims to summarise the up-to-date knowledge and provide an overview of the state-of-the-art methods and key developments in the various subdomains of the field. The second offers a wide-ranging list of areas where Operational Research has been applied. The article is meant to be read in a nonlinear fashion. It should be used as a point of reference or first-port-of-call for a diverse pool of readers: academics, researchers, students, and practitioners. The entries within the methods and applications sections are presented in alphabetical order