Network Capital cost per user Cost per MByte LANs £200 ? very low ISDN, Basic Rate £800 £0.05 to £0.10The cost of broadband circuits such as SMDS and ATM are an unknown quantity. Most of these systems are still at the trial stage. However the cost of sending information over a WAN is likely to remain high. The cost of provision of large bandwidth on LANs will also rise as users adopt multimedia. This will force users to choose the most economical access mode for multimedia.
A file transfer can be initiated manually or automatically at any time. If done in advance of the anticipated time of use of the application, quite large files can be transferred. ISDN can typically transfer about 1 MByte of data per minute, which means that all but the largest multimedia applications, and large sections of video can be comfortably transferred in reasonable times.
Electronic mail systems are increasingly multimedia aware. Both X.400 and the Internet MIME standards can deliver audio, images, pictures and video. The recipient of the mail will of course need to have software integrated into the mail system which can recognise these data types and play them. Electronic mail can take longer to deliver than a file transfer, but has the advantage of being able to be used at any time in the absence of the participants.
A real time multimedia connection is the most demanding multimedia access mode. File transfer and electronic mail do not require a sophisticated, high capacity, or isochronous network to travel over. But real time multimedia demands the correct information at the right time. Users expecting real time pictures or sound are intolerant of delays in reception. Response times need to be of the order of one second. Delays in audio need to be under 150 milli-seconds to avoid echo.
Currently a lot of the media coverage of multimedia is oriented towards the possibilities of real time video applications such as video on demand, video conferencing etc., but it is likely to be applications such as multimedia electronic messaging and transfer of multimedia material between businesses that will become the workhorses of multimedia. In education non-real time use of multimedia material will also prove easier to set-up, and cost effective.
A series of questions can be posed. The reader can no doubt add more.
Question. Is real time interaction with another human, machine or application really needed?
Result. If real time interaction is a requirement the nature of the interaction must be established. A simple yes /no or mouse movement is not so network demanding as a video phone conversation. The response times will also need defining.
Question. What are the criteria for access and response times for different activities to be transacted between the user and the application.
Result. Users may not require instantaneous access to an application. For instance downloading of software off a file server to a class of students could take place while a lecturer is introducing the application.
Question. What is the length of time over which the application will be used?
Result. Over a long session there will be opportunities for information to be fetched over a network as a background task. This reduces the requirement on the network and the application.
Question. Will the user or student be using the application on a scheduled or timetabled basis?
Result. If the student or user is scheduled to use an application, then the material can be made available locally using a timed download.
Question. How many simultaneous users of the application are expected?
Result. A class of 10 students all trying to video conference with a tutor will quickly bring an Ethernet network to its knees. Is the use of multicasting techniques appropriate. Do all users have to perform the same tasks at the same instant?
Question. Over which networks will the application be fetched or used?
Result The network type available will constrain the use of some applications, such as video.
Question. What is the capacity of the network at the likely time of use?
Result Network capacity varies. A university LAN will be exceptionally busy during the middle of the day. If your application expects data which must travel on that network then delays can be expected.
Question. Are there network usage cost considerations, either for hardware or running costs?
Result Do not design a multimedia application largely based on the use of video conferencing over ISDN and expect a small telephone bill.
Question. Which computing platforms, networks and protocols will the application use?
Result. You will reach the widest audience or market if your application is cross platform, able to use more than one type of network and can be configured for different protocols.
Question. Can existing applications be used ? e.g. an e-mail or slide presentation.
Result No need to design your own?
Question. Can recognised standards be used in design the software.
Result If recognised standards for information and communication are used your material will be re-usable and accessible by others.
Question. Can the package be designed in a modular form?
Result A large multimedia package if broken into several modules may be more efficiently transportable across a network.
Question. How much application data and executable code needs to be down loaded?
Result The load on a network can be reduced and response times improved if file sizes are kept small.
Question. Can remote users be given regular updates of the package or data?
Result The application can be given a new look or improved facilities. This is particularly relevant to remote information kiosk design.
There are a few common rules linking the questions above. These are :-
You are considering using video conferencing. Will a video messaging facility suffice? Can the same aims be accomplished using voice and still image transmission?
In an information kiosk design can updates of information be kept to text only.
You are choosing an authoring platform. Can the platform accept common media formats, and access data or applications and outside of its immediate environment?
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