1. Real-Time Processing Systems:- A real-time provessing system is a parallel time relationship with an on-going activity which is producing information quickly enough to be useful in controlling the current life and dynamic activity. Thus the word "real time" describes a direct access or on-line processing system with severe time limitations. A real-time system uses direct-access processing but a direct-access system need not be operating in real-time. It is also possible to have a direct access system that combines immediate access to records for inquiry purposes with periodic transaction input and updating of records from a central collecting source. Such a system would meet many needs and would be simpler and less expensive than a real-time system.
Example:- The reservation system by air-line, hotels are examples of real time systems.
SOME IMPORTANT REAL-TIME SYSTEMS:-
1. NIC NET:- It is a nation wide computer network managed by National Informatic Centre (NIC) under the planning Commission Government of india. "NIC-Net" is a satellite based network with mother station at New Delhi and mini earth stations at ll state capitals, district headquarters. During next Five Year Plan, NIC is likely to launch its own satellite to support the NIC NET. This network is meant for use by all the civil government agencies for official purpose and has inbuilt security measures incorporated for on-line working/transfer of data between the work stations. In addition a number of public booths are being installed in various state capitals for providing access to General Information System on terminals of (GIST NIC) for public use. GIST NIC provides information of general nature on agriculture, industry, education, medical facilities, tourism etc.
2. INDONET:- This all india computer network is managed by computer Maintenance Corporatuon (CMC), a government enterprise. It aims at providing computing facilities to large segment of computer owners/users. The power of main frame computers of CMC is made available to the computer users over packet switched public Data Network (PSPDN) provided by Department of Telecommunication (DOT). PSPDN also provides access to the Gareway Packet Switching System (GPSS) at Bombay to varrious international data bases from mini packet switches located at Bangolare, Pune, Hyderabad and Dehli. This facility would be progressively extended to other cities as well.
Time sharing and Remote Computing service systems:- Time sharing is a general term used to describe a processing system with a number of relatively low speed, on-line and simultaneously usable stations. Each station provides direct assess to CPU. The use of special programs allow the CPU to switch from one station to another and to do a part of each job in an allocated "time slice" until the work is completed. The speed is such that the user has the illusion that nodody else is using the computer. Time-sharing and remote computing service organisations generally offer a library of on-line applications programs to their clients who need to supply only input data and access to the programs to obtain described information. INDONET works on these basis only.
Electronic Mail/Message System:- These messages begin and end at communicating word process/PC'S/other I/O devices on a LAN. Network computers are used to temporarily store and route the messages.
Data Base Retrieval System:- Organisations and individuals maintain a countless number of databases in computer accessible from for their private uses. There are also many data base producers who amaze and update information on specific subjects for public use. The access rights are then sold to an on-line service organizatiin.
Telecommunications Service:- Large number of people do much of their work on PC'S and word processors. These devices located at home are linked to outside office systems by telecommunication network. The need to commute to downtown physically is being questioned of course, telecommuting approach is not for everyone. Some people prefer social environment but telecommuting helps those who prefer flexible working hours at home.
Distributive Data Processing Networks (DDPN):- The relatively high cost of computer hardware in the 1960's spurred many organisations to establish a large central computer system and then to achieve economics by sharing the time of that system among many users. With crash of hardware prices many organisations have setup their own time-sharing system using terminals linked to it's own hardware.
When one or two processors handle the work load of all outlying terminals, the word 'timesharing' is probably still accurate. But when many geographically dispersed or distributed independent computer systems are connected by a telecommunications network and when messages processing tasks, programs, data and other resources are transmitted between cooperating processors and terminals, the term time sharing may not be broad enough.
Distributed Data Processing (DDP) network is often used to describe this extension of time sharing. DDP arrangements may be defined as one that places the needed data alongwith computing and communication resources neccessary to process this data at the end-user location. This may result in many computers and significant software resources being shared among large number of users. NIC NET and INDO NET fall in the category of DDP networks.
NETWORK CONFIGURATION:- Some possible Distributed Data Processing configurations are:-
1. Star DDP Network:- A central host computer (s) communicates and controls a second level of sattelite or node processors. These nodes in turn communicate with I/O terminals.
2. Hierarchical variation star DDP Network:- Here the central host computer (s) is still linked to regional node processors but these regional nodes may in turn act as hosts to subordinate small processors. In addition to processing local applications, the small third level processors may support local level intelligent terminals. NIC NET has adopted this configuration with some variation.
3. Ring DDP Network:- It ia a non-host ring arrangement of communicating equals. Each ring processor may have communicating subordinates but within the ring there is no master computer.
ADVANTAGES OF DATA NETWORKS:-
1. Sophisticated computers and a growing library of application programs is available to end-user when needed.
2. Skilled computer/communication specialists can be made available to help network users to develop their own specialized applications.
3. Availability of multiple processors in the network permit peak load sharing and provides back up facilities in the event of equipment failure.
4. Users with the access to nearby computers and database may be able to react more rapidly to new developments.
5. Telecommunication costs can be lower when much of local processing is handled by on site computers.
DISADVANTAGES OF NETWORKS:-
1. The reliability and cost of telecommunication facilities used and the cost and quality of the computing service may be disappointed to some users.
2. Security provisions for protecting confidentiability and integrity of the user programs and data are generally ineffective.
3. Today data network environment is dynamic and turbulent and lack of computing/communications standards make it difficult to merge the equipment from different vendors into a smoothly functioning entity.
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