105 research outputs found
GUIDELINES FOR THE DESIGN OF ENHANCED, COST EFFECTIVE NETWORKS IN A MANUFACTURING ENVIRONMENT
Investigations into the transmission of real-time interactive speech over local area
networks (LAN) in an industriai/commerciai environment to eventually obviate the
need for a private automatic branch exchange and ultimately prepare the way for a
single interactive integrated information system (PS) that provides work stations, which
are networked via a LAN, with a fully interactive speech and graphics facility
commensurate with the future requirements in computer integrated manufacturing
(CIM).
The reasons for conducting this programme of research were that existing LANs do not
offer a real time interactive speech facility. Any verbal communication between
workstation users on the LAN has to be carried out over a telephone network (PABX).
This necessitates the provision of a second completely separate network with its
associated costs. Initial investigations indicate that there is sufGcient capacity on
existing LANs to support both data and real-time speech provided certain data packet
delay criteria can be met.
Earlier research work (in the late 1980s) has been conducted at Bell Labs and MIT.
[Ref 25, 27 & 28], University of Strathclyde [Ref 24] and at BTRL [Ref 22 and 37].
In all of these cases the real time implementation issues were not fijlly addressed. In
this thesis the research work reported provides the main criteria for the implementation
of real-time interactive speech on both existing and newly installed networks.
With such enhanced communication facilities, designers and engineers on the shop
floor can be projected into their suppliers, providing a much greater integration
between manufacturer and supplier which will be beneficial as Concurrent and
Simultaneous Engineering Methodologies are further developed.
As a result, various LANs have been evaluated as to their suitability for the
transmission of real time interactive speech. As LANs, in general, can be separated
into those with either deterministic or stochastic access mechanisms, investigations were
carried out into the ability of both the:
(i) Token Passing Bus LANs supporting the Manufacturing and
Automation Protocol (MAP)—Deterministic
and
(u) Carrier Sense Multiple Access/Collision Detection (CSMA/CD) LANs
supporting the Technical Office Protocol (TOP)— Stochastic
to support real time interactive speech, as both are used extensively in commerce and
manufacturing.
The thesis that real time interactive speech can be transmitted over LANs employed in
a computer integrated manufacturing environment has to be moderated following the
tests carried out in this work, as follows:-
The Token Passing LAN presents no serious problems under normal
traffic conditions, however, the CSMA/CD LAN can only be used in
relatively light traffic conditions i.e. below 30% of its designed
maximum capacity, providing special arrangements are made to
minimise the access, transmission and processing delays of speech
packets.
Given that a certain amount of delay is inevitable in packet switched systems (LANs),
investigations have been carried out into techniques for reducing the subjective efifect
of speech packet loss on real-time interactive systems due to the unacceptable delays
caused by the conditions mentioned above
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Advances in local area optical data communication systems
This paper reviews optical fibre technology for local area optical communications systems. Technologies used in local systems include single and multimode fibre, single and multimode lasers, optical modulators, photodetectors, wavelength division multiplexing, multilevel modulation formats, electronic packet switching, electronic equalization and error correction. These methods have enabled the local area optical link data rate to increase from 0.1 Gb/s in 1990 to nearly a Tb/s in 2019. The challenges to increasing link data rates further, whilst reducing the transmitted power per bit, at reduced cost are discussed. Potential technical solutions and newly proposed methods which might address these challenges are highlighted
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Wavelengths switching and allocation algorithms in multicast technology using m-arity tree networks topology
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.In this thesis, the m-arity tree networks have been investigated to derive equations for their nodes, links and required wavelengths. The relationship among all parameters such as leaves nodes, destinations, paths and wavelengths has been found. Three situations have been explored, firstly when just one server and the leaves nodes are destinations, secondly when just one server and all other nodes are destinations, thirdly when all nodes are sources and destinations in the same time. The investigation has included binary, ternary, quaternary and finalized by general equations for all m-arity tree networks.
Moreover, a multicast technology is analysed in this thesis to transmit data carried by specific wavelengths to several clients. Wavelengths multicast switching is well examined to propose split-convert-split-convert (S-C-S-C) multicast switch which consists of light splitters and wavelengths converters. It has reduced group delay by 13% and 29% compared with split-convert (S-C) and split-convert-split (S-C-S) multicast switches respectively. The proposed switch has also increased the received signal power by a significant value which reaches 28% and 26.92% compared with S-C-S and S-C respectively.
In addition, wavelengths allocation algorithms in multicast technology are proposed in this thesis using tree networks topology. Distributed scheme is adopted by placing wavelength assignment controller in all parents’ nodes. Two distributed algorithms proposed shortest wavelength assignment (SWA) and highest number of destinations with shortest wavelength assignment (HND-SWA) algorithms to increase the received signal power, decrease group delay and reduce dispersion. The performance of the SWA algorithm was almost better or same as HND-SWA related to the power, dispersion and group delay but they are always better than other two algorithms. The required numbers of wavelengths and their utilised converters have been examined and calculated for the researched algorithms. The HND-SWA has recorded the superior performance compared with other algorithms. It has reduced number of utilised wavelengths up to about 19% and minimized number of the used wavelengths converters up to about 29%.
Finally, the centralised scheme is discussed and researched and proposed a centralised highest number of destinations (CHND) algorithm with static and dynamic scenarios to reduce network capacity decreasing (Cd) after each wavelengths allocation. The CDHND has reduced (Cd) by about 16.7% compared with the other algorithms
Wavelength and time division multiplexing with lightpath trespassing for all-optical star local area networks
Many medium access control protocols have been proposed for optical wavelength division multiplexing local area networks with a star topology. These protocols range from those based on the concept of fixed-assignment of communication subchannels, such as TDMA (Time Division Multiple Access); reservation of communication subchannels, such as DAS (Dynamic Allocation Scheme); or random-access to communication subchannels, such as DT-WDMA (Dynamic Time-Wavelength Division Multiple Access). In addition various hybrid protocols have been considered, for example, protocols incorporating both fixed-assignment and reservation rules, such as HTDM (Hybrid TDM). This thesis is on a novel hybrid protocol of fixed-assignment and random-access called "WTDMA with lightpath trespassing". This protocol combines the most desirable aspects of fixed-assignment and random-access protocols, while limiting their drawbacks. The performance of different versions of the protocol are analysed both mathematically and by stochastic simulation. The obtained results justify the introduction of the WTDMA with trespassing protocol, and indicate the situations where its use is advantageous
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