Guidelines For The Design Of Enhanced, Cost Effective Networks In A Manufacturing Environment

Abstract

Investigations into the transmission of real-time interactive speech over local areanetworks (LAN) in an industriai/commerciai environment to eventually obviate theneed for a private automatic branch exchange and ultimately prepare the way for asingle interactive integrated information system (PS) that provides work stations, whichare networked via a LAN, with a fully interactive speech and graphics facilitycommensurate with the future requirements in computer integrated manufacturing(CIM).The reasons for conducting this programme of research were that existing LANs do notoffer a real time interactive speech facility. Any verbal communication betweenworkstation 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 itsassociated costs. Initial investigations indicate that there is sufGcient capacity onexisting LANs to support both data and real-time speech provided certain data packetdelay 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. Inthis thesis the research work reported provides the main criteria for the implementationof real-time interactive speech on both existing and newly installed networks.With such enhanced communication facilities, designers and engineers on the shopfloor can be projected into their suppliers, providing a much greater integrationbetween manufacturer and supplier which will be beneficial as Concurrent andSimultaneous Engineering Methodologies are further developed.As a result, various LANs have been evaluated as to their suitability for thetransmission of real time interactive speech. As LANs, in general, can be separatedinto those with either deterministic or stochastic access mechanisms, investigations werecarried out into the ability of both the:(i) Token Passing Bus LANs supporting the Manufacturing andAutomation Protocol (MAP)—Deterministicand(u) Carrier Sense Multiple Access/Collision Detection (CSMA/CD) LANssupporting the Technical Office Protocol (TOP)— Stochasticto support real time interactive speech, as both are used extensively in commerce andmanufacturing.The thesis that real time interactive speech can be transmitted over LANs employed ina computer integrated manufacturing environment has to be moderated following thetests carried out in this work, as follows:-The Token Passing LAN presents no serious problems under normaltraffic conditions, however, the CSMA/CD LAN can only be used inrelatively light traffic conditions i.e. below 30% of its designedmaximum capacity, providing special arrangements are made tominimise the access, transmission and processing delays of speechpackets.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 efifectof speech packet loss on real-time interactive systems due to the unacceptable delayscaused by the conditions mentioned above.

Date of Award	1994
Original language	English
Awarding Institution	University of Plymouth