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Multimedia in the Teaching Space
4 ROLE OF NETWORKS WHEN USING MULTIMEDIA INFORMATION.
4.1 PRESENTING MULTIMEDIA INFORMATION
Most university campus will be limited in the bandwidth available in their networks, often about 100Mbps Ethernets, which means the maximum available to individual users is likely to be about 10Mbps. With time further bandwidth will become available and then the ability to handle multimedia information will be more assured.
Two scenarios will be common; first the presentation of multimedia material in the teaching space which is being relayed over the local area network from a network server and secondly by the use of standalone systems. When the networks are used, there are two principle methods in use; either the material may be multicast to a number of sites simultaneously over the MBone, or multipooint ISDN configurations can be used. In either case teaching can be carried out to distribution of sites collaborating in a shared teaching programme.
The MBone operates on the INTERNET, and is designed to link a number of sites but uses pathways which minimise the traffic on the INTERNET, by sharing routes between sites as much as possible. The MBONE can be used interactively, permitting each site to communicate with every other in the session.
This is different to multipoint ISDN conferences between a number of sites simultaneously, where all sites are connected to a central Multipoint Control Unit (MCU). The switching of the MCU is commonly by voice activation, so that the site where the audio is active, is transmitted to all receiving sites. This system until recently required that all sites were operating at the same bandwidth (e.g. 128Kbps for ISDN-2), which resulted in the whole network having to operate at the speed of the slowest partner. Recent advances will permit mixed working thus permitting some sites to use their equipment capable of operating at 384Kbps and higher resolution, and at the same time allowing smaller sites to be part of the conference with their equipment only operating at 128Kbps.
The multimedia material used in teaching applications can be delivered to the user over a variety of types of networks, which can be internal departmental or campus LANs or they can be wide area networks (WANs) linked to various regions and institutions, supported by the academic networks (JANET and MANs) or by public service provider such as ISDN. Each of these technologies will be discussed in this paper.
It is assumed that the higher the sophistication of the supporting information in teaching and learning the better it is for the student. This greater sophistication requires more effort in the production, and more sophisticated equipment for the presentation, so the teacher should always ask what is the simplest and clearest way of presenting information consistent with the use of the material. A high resolution picture is not any advantage to the student if the information could be presented perfectly adequately as a line drawing. As multimedia is expensive to produce and to present it's use must be justified. High resolution images are good to look at but the added detail must contribute something positive to the student's knowledge.
The advantage of multimedia is the ability to bring together a number of different media in a way which permits synchronisation of information, e.g. vision and sound, and which overall enhances the information. It should be remembered that the "people" themselves can provide information in several media naturally, e.g. the patient demonstrating a particular clinical situation provides visual, tactile and even olfactory information of signs and symptoms, as well as being able to describe and be questioned about the effects of the disease. Another example is the ability to link into the teaching space people over remote video links which can provide visual and audio information from a distance, e.g. the application of open and distance learning techniques.
In practice the good use of multimedia gives the teacher opportunities to provide a number of stimuli to the students, which can make the teaching much more comprehensive and interesting. The ability to provide more varied stimuli to the teaching and learning process can also include the student working on his/her own; the ability to present on the computer screen in a variety of coloured images, and sound effects can enhance the information being presented to the student. The eye is undoubtedly attracted by colours and shapes and these are most frequently used to attract the interest of the student.
If legacy network, such as optical fibres carrying analogue audio-visual signals still exist in an institution they can be used to good purpose. For example in the TLTP INSURRECT project a SONY LVR videodisc server was used to store still and moving images and the LIVENET optical fibres, were used to take these analogue images into the teaching space. Also they carried the images to CODECs for transmission to remote teaching sites over the SuperJANET ATM video network. The SONY video server stored up to 54,000 image frames as either still images or short video sequences. This SONY system could be controlled using RS232A commands, transmitted either over the LAN or over the INTERNET from remote sites. Thus it was possible to control slide-shows easily from a laptop in the lecture theatre, either within the same institution or remotely. Video sequences could also be controlled in an interactive manner; stopping, starting and playing backwards and forwards. In the future the digital network will increasingly pervade the whole campus, but it must be remembered that the analogue network is likely to provide a higher bandwidth and therefore higher resolution images.
In the INSURRECT project; LIVENET analogue circuits were used to transmit video and audio signals around the UCL campus, and also were fed into CODECs to be transmitted over the SuperJANET ATM video network to the remote sites. One site (Bristol) was not on SuperJANET, and TCP/IP was transmitted over a 100Mbps SMDS link very successfully. In the early part of the experiment there was some difficulty synchronising the voice channel with the video but this was improved during the lifetime of the project.
Ethernet LANs are common in university campus which are capable of providing good resolution signals using IP into the teaching space but there is no bandwidth reserved for the video signal, and thus the quality of the signal will vary according to the level of usage of the Ethernet. It is notable that current LAN video conferencing systems are using IP for the campus networks, but use an ISDN gateway to connect with remote sites because the guaranteed bandwidth available on ISDN ensures that the picture quality can be maintained.
ATM networks can be used with typical bandwidths of 25Mbps to 155Mbps, both in LANs and WANs. ATM networks are often used as a transport medium carrying a number of protocols such as IP, SMDS and LAN Emulation. In some applications native ATM technology is utilised to transmit the audio and video information. In many campus networks there is a mixture of different technologies in use; a typical scenario would be an ATM backbone with Ethernets connected. As far as possible the ATM backbone should be routed close to major teaching areas.
When teaching there is frequently a need to link more than two sites, and then Mbone and multipoint configuration are necessary. A multipoint conference uses a star network configuration, and is capable of being interactive as each port on the MCU will support two-way video and audio. The audio signal is used to control the switching in voice switching systems.
Multi-casting is particularly relevant to IP networks, and the Mbone has been developed to economise/minimise the traffic on the network by choosing routes between all sites so that as much as possible of the traffic can share the same routes and branching out in the final stages of the links. Ideally the multi-cast network will link all sites to each other and further this network can support interactive traffic. This will be considered in more detail in section 4.4.
ISDN -- Integrated Services Digital Network -- is a telephone service that enables you to have high-speed data connections through your phone line. ISDN is basically the telephone network turned completely digital, using existing wiring. ISDN is capable of transmitting large amounts of data rapidly between sites, and it is possible to support compressed video transmission because the bandwidth is guaranteed and therefore the audio and video synchrony of the signal is maintained.
ISDN is much cheaper than many other methods of moving data at high speeds, but it is still expensive relative to a normal phone line. Normal phone lines -- the kind that work reliably with your 14.4Kbps modem, fax, answering machine, are known in some circles at POTS-- plain old telephone service. There are serious attempts to provide video on these circuits as exemplified by video-telephones, but these in general do not provide the resolution necessary for teaching.
A major drawback to ISDN is that because it moves digital data instead of analogue data, it doesn't work with your regular modem, or answering machine. You need special, expensive equipment to perform those functions at ISDN speeds. However, ISDN is faster than a standard modem, and is available in various parts of the world, including Australia, Western Europe, Japan, Singapore, France, and portions of the U.S.
There is listed below three web sites which give very comprehensive information about ISDN, and include reference to the operation of ISDN in a number of different countries.
Graphics Multimedia Virtual Environments Visualisation Contents