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Data communication policy 20 May 1998 1/3
Data communication under HP
The bulk of the data can be transported by p...
Data communication policy 20 May 1998 2/3
UHD diskettes can cater for most of the data transport requirements. Only at off...
Data communication policy 20 May 1998 3/3
Obviously, wherever the need of rapid data transport arises alternative telecomm...
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Download-manuals-general-note ondatacommunication


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Download-manuals-general-note ondatacommunication

  1. 1. Data communication policy 20 May 1998 1/3 Data communication under HP Summary The bulk of the data can be transported by physical media like diskette and CD-R. Standard STD dial-up lines can be used to transport small amounts of data and for quick data exchange. Decisions on special high capacity data communication facilities, if needed, should be taken individually, i.e. tailored to the specific requirements. The policy in this respect should be to take irrevocable decisions only at the latest moment, to maintain maximum flexibility and to benefit from the latest technological improvements. Developments in the communication industry are to be closely monitored. Scope The Hydrological Information System as currently being developed/improved under the Hydrology Project (HP), aims at making authenticated data available to hydrological data users. Hydrological data are collected in the field, entered into computer systems, validated and processed in data processing centres and eventually stored in data storage centres. The Hydrologic Data Users (HDUs) may access the data storage centre(s) to collect the required data. Along the chain of data handling and processing, from the field station to the data storage centre and the HDU, the data have to be transported from one centre of activity to the other. The data transport shall be reliable, cost-effective and timely. The choice of the method of transport depends on a number of factors i.e. availability of data transport channels, ease of use of the same, transport time, cost, reliability and others. For different data transport paths, e.g. from a divisional office to the data processing centre, an assessment of the optimum method has to be made. Data can be transported in two ways, i.e. recorded on physical data media and by telecommunication. Data volumes In the sequence of subsequent data transport events from the field to the data centres, data of multiple sources are combined into increasing volumes. At the data entry level, the monthly volume is expressed in kbytes per station, and grows to several Mbytes at the divisional level and further increases to many Mbytes along the circuit to the data centres. The ever-growing amount of data in the Data Storage Centres will be expressed in Gbytes. The format in which data are transported, strongly affects the data volume, e.g. equidistant time series can be transported in a ‘timeless’ format, which only contains the date and time of the beginning of the data series and the sample time interval. Using standard compression techniques, data can be squeezed into a space efficient representation. Transport by physical media One consideration regarding the selection of the transport medium is that physical data media can transport any amount of data. Moreover, the physical data carriers have low running costs, are widely available and are easy to use. For routine data transport, it is therefore recommended to implement a data transport system based on physical media. The choice of medium depends upon the amount of data to be transported. Essential considerations are the availability, standardisation and reliability of the proposed media. In a PC environment, well-established data transport media are various types of diskette and CD-R. The large capacity gap between the common diskette and the CD-R is filled by the emerging HiFD and LS-120 Ultra High Density UHD standards which feature capacities of 200 and 120 Mbyte diskettes respectively. Both standards are backward compatible with 1.44 MB HD diskettes. Presently, it is unclear which of the two will get full market acceptance. The Hydrology Project should adopt one UHD version only. A decision in this matter is not required yet, but in 1999 a decision should be taken. For compatibility and efficiency reasons, all offices should have at least read access to each of the three media. Both the HD and
  2. 2. Data communication policy 20 May 1998 2/3 UHD diskettes can cater for most of the data transport requirements. Only at offices where large amounts of data, e.g. more than 1 Gbyte at a time, are routinely generated for transport, CD- recorder support is required. As per convenience the media can be hand carried or sent by post, express mail, or courier. Transport by telecommunication The delineated physical data transport concept caters for all routine data transport at a very low cost. However, a drawback of this concept is the duration of point to point transport, which can amount to several days. In the context of the applications and the processes involved, i.e. generation of valid and authenticated hydrological data, apparently there is no basic need for fast data exchange. However, while processing data a necessity for additional and or revised data may emerge. Then, it is desirable/required to have the data quickly available. This could be achieved by way of telecommunication. Limited amounts of data, e.g. up to several Mbyte, can be efficiently transported over standard DoT dial-up lines. If the now widely available Internet is used, then data exchange methods like e-mail and FTP (File Transfer Protocol) can be applied. Most Internet service providers charge an annual fee for the services. The cost for telephone connection-time in most cases is limited to the local call tariff only. This as opposed to a point to point connection over dial-up line; then the cost will based on the STD tariff for that distance. A major limitation of dial-up telephone is the throughput rate, which on standard dial-up lines of good quality can be about 2000 to a maximum of 3000 bytes per second. On lower quality lines, the throughput rate severely deteriorates. At a rate of 2000 bytes per second, it will take at least 720 seconds, i.e. 12 minutes to transport 1.44 Mbyte of data (the contents of a diskette). Hence, communication over dial-up line is not a convenient way to transport large amounts of data, but it is useful for interactive data exchange. The standard NICNET data rates are 1200 and 9600 bits per second, i.e. 120 to 960 bytes per second, which makes NICNET a rather slow system. In addition to that, the data have to be transported to the local NICNET communication centre, either physically or by DoT and consequently this adds to the total throughput time. Furthermore, most NICNET stations operate during office hours only. Data exchange between state data centres In most states the data processing centres and the data storage centre are accommodated in a single building. The data exchange is conveniently based on LAN technology. However, in some states the SW and GW data processing centres are planned to be established at different locations, in one case in two different cities. Permanent interconnection between such centres by LAN technology is rather costly, as it requires continuous access to a data communication infrastructure, e.g. a leased line. The cost of leased line increases drastically with distance and capacity. A standard grade leased line has a capacity similar to that of a dial-up line. Hence, the throughput rates are also similar. The rental cost of leased line may be deemed prohibitive. It is envisaged that the need for data exchange can be catered by physical transport for the bulk of the data, augmented by data communication over dial-up STD line. Data exchange with other data centres at national and state level The Hydrology Project generates validated and authenticated hydrological data, which are stored and maintained in a database for use on project basis. The hydrological data are not generated for daily operational use. This implies that there is no real-time aspect in data exchange. Consequently, the data exchange between the data centres may be organised in a similar way as within the states, i.e. based on physical media and augmented by dial-up STD.
  3. 3. Data communication policy 20 May 1998 3/3 Obviously, wherever the need of rapid data transport arises alternative telecommunication systems may be considered. In this respect, preference should be given to the internationally standardised communication protocols that are implemented in standard software. The alternative telecommunication systems have to be evaluated for cost effectiveness, reliability, availability, support and throughput time. The software environments, yet to be implemented, do not inhibit addition of advanced data communication facilities, provided that the communication is based on widely supported international standards. Data dissemination to HDUs The Hydrological Data Users have somewhat different requirements in the sense that they do not deliver data but only collect data. Actually, their way of use is quite similar to the common mode of Internet access: the user searches the Internet for the required data, makes his selection and subsequently downloads the data to his site. Initially, at the early stage of implementation, such a facility can be made available in an Intranet setting, i.e. the HDU has to present himself to the data centre where he may get access to the data over the LAN in Intranet fashion. Later, the Intranet technology can easily be extended to the Internet. However, since the Internet is a public network, security measures should be implemented. The data search and selection processes may be executed over STD but most likely the selected data will not be disseminated by STD but on diskette (HD or UHD) or CD-R instead, possibly protected by encryption. Policy The depicted data transport methodology, i.e. transport by physical media, augmented whenever required with data communication over dial-up STD lines, is very cost effective and should be implemented regardless of any other system, at least as a back-up. It is anticipated that during the implementation of the Hydrology Project, data communication technology will change considerably. Most likely, the data communication performance and the services provided will improve. Presently, no data centre is functional according to the HIS specifications. First the dedicated software has to be implemented and the data base established. Not long before the data centres become fully operational, the final decisions on the data exchange between the top level data centres have to be made. It is anticipated that in the meantime, the telephone system will be further expanded and improved. Moreover, data communication technology evolves at high speed and new services are introduced in rapid succession. In this context, the policy should aim at introduction of more advanced communication systems only when they become required and are feasible to avoid implementation of technology that is bound to be obsolete at the time the need for it arises.