5: DIGITAL TERRESTRIAL NETWORKS
Steve Wheeler
Training Manager
RATIO Project
Sidney White
Telematics Researcher
WIRE and RATIO Projects
University of Plymouth, UK
Key Words: Telematics, Distance Education,Convergent Technologies, ISDN, Digital Networks, Information Superhighway
Introduction
This series of articles has highlightedthe development of telematics and its applications to teaching and learning,particularly within the open and distance learning context. The currentrapid convergence of technologies will enable the development of hybridapplications which use TV and computer technology, resulting in opportunitiesfor greater interactivity between users and the services on offer. For example, viewers of television programmes will be able to do more thancontrol the choice of viewing channel or whether or not they incorporateteletext. They will also be able to select the kind of news storiesand topics they wish to see, for example entertainment news or politics. They will be able to place orders with an advertiser as the commercialappears on their screens. They will be able to watch live sportand request replays at any stage of the action, and this could be fromany camera angle. Applying these concepts to education and trainingmay require a quantum leap of imagination in order to exploit the capabilitiesof technologies which will soon be available on a widespread basis.
Moreover, convergence is not limited totelevision. In the UK, Virgin Radio and other commercial stationsare now being transmitted to listeners by satellite and on the Internetas well as by conventional terrestrial transmission routes.
Underpinning the majority of convergenttechnologies are the rapidly advancing capabilities of digital terrestrialnetwork services. Terrestrial networks are based on underground cablingand microwave relays as opposed to satellite transmission.
Communications companies are quick to extolthe virtues of digital network services. Why not change the way wework? was the poignant question posed during a recent media advertisingcampaign by British Telecom with the public being alerted to the benefitsof ISDN by advertising hoardings, radio and TV adverts. Because suchcampaigns have largely targeted the business market, many people tend toassume that businesses are the only beneficiaries of the technology. However, with prices dropping continually and the network provision expandingthe authors predict that the entire UK population will benefit from digitalservices in the next few years.
This fifth article in the ITIN series ontelematics applications seeks to describe some of the applications of digitalterrestrial network services, and how teachers and learners will benefitfrom this technology over the next decade.
Integrated systems
ISDN stands for Integrated Services DigitalNetwork. ISDN enables the integration of one computer with others in orderto provide the user with a service. Computers generate digital commandsor signals, which in a conventional setting require a modem to connectthem to the telephone network in order to send and receive these signals. The modem converts digital signals into audio signals which are then transmittedalong the line. At the receive end, another modem performs a complementaryrole, translating the audio tones back into digital format so that thereceiving computer can use it. ISDN technology ensures that computerscan communicate completely in digital format without the need for modems.
The nature of ISDN
ISDN is a truly hybrid system in that itutilises old and new technology. It more often than not employs 'twistedpair copper wire', the ubiquitous conductive cable that supports the PublicSwitched Telephone Network (PSTN) which constitutes the world's terrestrialtelephone network. With twisted pair widespread across the globe, and moreimportantly still in good condition, telecommunications companies cannotafford to ignore its continued usefulness. ISDN installation is now onthe rise world-wide. The swift advances achieved in computer andcommunications technologies have guaranteed that the development of integrateddigital systems has also steadily progressed.
Some countries have committed copious timeand resources into introducing ISDN, and the concomitant building up ofcustomer confidence in a digital alternative. At the time of writing,British Telecom (BT) claims it is installing 2000 new ISDN lines each week. ISDN is not limited to twisted pair cabling alone, operating just as efficiently using other routeways such as coaxial cable, microwave transmissionand optical fibre cabling.
The benefits of ISDN
It has long been the desire of both futurists and technologists to have a 'one stop' communications link for both the home and office. The saving of time and effort for those wishing to exploit the latest communications innovations make it a clear alternative and ISDN is a step closer to realising that goal. At present one ISDN line can facilitate the use of telephones, e-mail, fax and answering machines without the tangle of multiple lines. Two telephone lines (ISDN2) can additionally give a reasonable quality of videoconferencing and all the benefits it brings, such as the potential for face to face tutorials and direct instruction at any distance. Videoconferencing was the subject of a previous article in this series 1 and is a particularly useful tutorial methodwhen applied to the support of distributed student groups.
The user costs are now downward in trend,following BT's recent announcement to charge the same price for singleanalogue and ISDN2 lines. Until recently, ISDN2 required the userto pay for two lines, but current pricing structures have meant that ISDN2calls now compare favourably with conventional analogue telephone callswithin the UK mainland.
Ultimately, the greatest benefit for businessand education is the increased capability of digital networks to rapidlytransmit large data volumes. The transmission of large volume filessuch as multi-media programs, for instance, would take a great deal longerif a modem/analogue system was used in comparison to ISDN. Less timewaiting to access information from remote websites means less time in whichinterruption in a data stream can occur.
Switching to ISDN offers increased bandwidthcapability. As previously stated, this means that ISDN offers fastertransmission rates. An increase in bandwidth can also mean a greaterchoice of applications, faster response times as well as less signal tonoise ratio (SNR) encountered with analogue links.
Because modern devices have the capacityto store and transmit an increased amount of information, the need to transferinformation as quickly as possible between points becomes less of a priority. To appreciate this we must imagine a stream of traffic trying to navigateits way through a single country lane whilst competing with a stream of oncoming traffic. For safety sake motorists must slow down and forgo thefull potential of their vehicles, occasionally pulling over in order toallow priority traffic such as emergency vehicles through. However,by using a motorway, which has many more lanes, motorists are quickly ableto reach their destinations, substantially reducing the occasions whenthey need to slow down for other traffic and can use their vehicles totheir full potential. ISDN is the equivalent of a motorway and the vehiclepotential we speak of is the digitisation of the transmitted information.
Increased bandwidth will be quite noticeableto users, particularly in the higher transmission rate of data. ISDNprovides data transmission over existing telephone cable at speeds in excessof 50 times that currently achievable in the analogue network. Thiswill enable a screen of information, such as a spreadsheet or document,to be transmitted in under a second compared to over 15 seconds in thepresent analogue network. A more complex screen involving high-resolutiongraphics can be transmitted in about five seconds via ISDN as opposed toover two minutes at current 28800 bit/s speeds. Students sendingwork to tutors for marking can thus expect to spend less time transferringfiles.
Another feature of ISDN is that less interferenceis experienced when information is transmitted. When the telephone systemamplifies (strengthens) the signal it also amplifies the background mushand unwanted background noise as well. Because ISDN is a digital systemmush and background noise is not repeated thereby giving the end user atrue reflection of the original signal.
Problems with ISDN
Allegations have recently been made in the communications and IT press about mysterious disconnection of ISDN lines from the exchange without the authority of the user. 3 This mayreflect the belief that ISDN provision in the UK is less sufficient thanwe have been led to believe and digital service providers may be monitoringlines to gauge usage. Discovering that a line has been disconnectedcan be disconcerting, embarrassing and frustrating, and it is worth rememberingthat a line should be tested if it has been left unused for a week or more. It makes little difference how advanced and leading edged a technologyis claimed to be, or what benefits are possible using computer mediatedcommunications. Students waiting to take part in a virtual conferencewill not wait long if simple connections do not function when they areexpected to.
Cost is an overarching consideration inthe implementation of any new technology, and high installation and rentalcharges levied by service providers is a bone of contention with many ISDNusers. These are the charges for initial connection to the digitalnetwork and the regular payments necessary to maintain the line. At the time of writing, BT's charge for ISDN2 installation is £199,with a quarterly rental bill of £133.75.
The quality of service offered by national telecommunications companies is disparate and appears to reflect each company's country of residence. A recent survey carried out by Data Communications magazine 4 rated Japan's Kokusai Denshin Denwa Co. Ltd. in top place for ISDN provision. Digital provision throughout Europe compared poorly with the rest of the world. ISDN provision in the UK is still patchy in a few regions, with some rural areas contending with particularly poor coverage. 2
ISDN Technical Configurations
In Europe, each digital channel has a bandwidth of 64 Kbps. Additionally there is a D channel which provides a 16 Kbps or 64 Kbps data pipe, although this is dependent upon the number of channels used. ISDN comes in various sizes 5 , and is generally configuredin multiples of 2 x 64 Kbps B channels. At the narrow bandwidth end, commonlyused for videoconferencing applications, is Basic Rate Interface ISDN (BRI),popularly known as ISDN2. Broadly speaking, ISDN2 is two lines mergedtogether to give 128 kbps.
ISDN6 (BRI) is a multiple of 6 x 64 KbpsB channels, giving a bandwidth of 384 Kbps. This bandwidth copies verywell with videoconferencing and will give a good quality graphics picture.
The Future of ISDN
The next millennium will undoubtedly producea greater variety, and as yet unknown sea of applications, heavy on memory,and hungry for bandwidth. The commitment towards, and development of integrateddigital systems may go some way to obviating the problem of bandwidth. There are some that argue, however, that it matters little how much bandwidthis offered. The demands of hardware and software manufacturersand users will simply rise to match the bandwidth available, resultingin log jams of data traffic.
If we are led to believe the futurist predictions,a vast amount of business and training is set to be conducted over theInternet. Those who have access to the Internet will have already experiencedthe frustrating effects of narrow bandwidths which result in slow connectivityand download time. Although digital connections such as ISDN willgo a long way in helping to alleviate these problems, they may never beeradicated completely as web graphics become even more sophisticated.
ISDN 2 is well suited to videoconferencing,as it benefits from a high speed service and a wider bandwidth. This meansthat more information can be transmitted along the connection in less timethan a telephone line. Videoconferencing requires as much bandwidth asit can handle, due partly to the fact that each pixel in a videoconferencingpicture has to be transported along the communications line as quicklyas possible in order to achieve an acceptable frame rate, and produce movingpictures. The frame rate for ISDN 2 is also faster than the PSTN, havinga frame rate of 15 frame per second or less, as opposed to a PSTN systemwhich can expect a frame rate of 10 fps or less. Full motion videois nominally 24 fps, so ISDN still has a long way to go.
The impact on education
By now, teachers and trainers may be askingthe question - exactly how will ISDN affect my practice as a teacher, andhow will it benefit my students?
One obvious answer is that ISDN will improvecommunications at a distance between teachers and their students. This will be particularly the case where a group of students is dispersedacross great distances. The authors argue that distance learningapproaches will be revolutionised by digital network technologies, muchthe same way that television revolutionised the entertainment industry. ISDN provides a high quality and easily accessible technology for learning,ensuring fast transmission rates, high quality and low error data transfer. ISDN fits in well with existing terrestrial telephone networks, but isalso flexible enough to be able to work on newer highways such as opticalfibre and microwave transmission routes.
Self directed study will be greatly enhanced,regardless of distance, simple because students will be able to gain increasedaccess to remote databases, graphical materials and interactive learningopportunities.
The interactive nature of open learningmaterials will improve due to digital transmission techniques. Thisis because more bandwidth is available with which to send and receive greateramounts of data, sound, video and graphics. It is conceivable thatmulti media packages containing full motion picture video and interactivenarrative texts could be accessed readily by remote students studying athome. For example, a student nurse learning ward management skillscould take part in a virtual ward management simulation using on-line materials. She could be presented with many hypothetical scenarios and asked to makedecisions based on the video materials in front of her. This learningin turn could be assessed at a distance, with the learner being interviewedvia digital video conferencing. There is of course no substitutefor having to deal with real life situations, but if the student is studyingaway from a clinical practice area, virtual on-line learning will becomea viable and effective alternative.
Studying at a distance requires that students gain access to quality learning experiences to replace the richness of social contact that may be lacking in traditional distance learning. Often this can only be achieved by the creation of opportunities to collaborate and share experiences, even if only in a virtual context. 6,7 The capabilities of digital systems allow several users to communicate simultaneously, creating the necessary collaborative learning environments. 8
Conclusions
It is becoming increasingly apparent thatas global communication requirements demand faster and more flexible solutions,so the technology must develop to keep pace. ISDN is the digitaltechnology presently filling the gap, and as user confidence increasesand the costs of installation and rentals reduces, the authors predicta greater proliferation of digital networks and associated applicationsaround the globe. Digital integrated services are not the futureof computer networking - they are the present.
The benefits to the domestic user havealready been outlined in the popular press. In the future it willbe possible for users to switch on lights, cookers and video recordersbefore they arrive home or even check to see if the dog is chewing thefurniture via home security cameras! All this should be possible usingan interface connected to a digital telephone network. The possibilitiesare endless. If a signal can be digitised, then a digital line suchas ISDN will be able to carry it, ensuring that the one stop interfaceenvisaged by the futurists becomes a reality. The benefits to educationand training will only be realised as educators come to terms with theastounding flexibility and ever growing speed of digital network capabilitiesand begin to apply them within the context of learning.
The final article in this series will attemptto offer a strategy for incorporating convergent technologies intoa coherent and sustainable framework for the support of open distance learning.
References
1. Wheeler, S. Distance education &new convergent technologies: video conferencing, Information TechnologyIn Nursing Journal, 1997; 9.1: 19-21.
2. .Net magazine ISDN survey, 1997.
3. Stallings, W. Advances in ISDN andB-ISDN. IEEE Computer Society Press, 1997.
4. Data Communications magazine. May 1996.
5. May M. Explain IT. Comment October1996.
6. Slavin, R. (1992) Co-operative learning. In M.C. Alkin (Ed.), Encyclopedia of educational research, New York, MacMillan,pp 235-238.
7. Johnson, D., & Johnson, R., (1987)Learning together and alone (2nd Edition), Englewood Cliffs, NJ: PrenticeHall.
8. Magee, R., & Wheeler, S., (1997)Distance education & new convergent technologies: computer mediatedcommunication, Information Technology In Nursing Journal, 1997; 9.2: 13-17.
Glossary of terms
B-ISDN abb. Broadband ISDN,normally greater than 2 Mbps data transmission rate
fps abb. Frames Per Second. The number of frames required for full motion video is nominally 24 persecond.
ISDN abb. Integrated Services DigitalNetwork
Kbps abb. Kilo Bits Per Second;a measurement in the speed of data transmission; kilo = thousand.
Mbps abb. Mega Bits Per Second;a measurement in the speed of data transmission; mega = million.
Modem abb. Modulator Demodulator- a device that translates digital signals into audio tones for transmissionacross telephone networks.
Pixel abb. Picture Element; thesmallest element on a TV or computer screen.
PSTN abb. Public Service TelephoneNetwork; The conventional terrestrial telephone network
This paper was published in the InformationTechnology in Nursing and Information Management Journal, British ComputerSociety, Nursing Specialist Group, Volume 9, Issue 5, October 1997.