Data communication policy 20 May 1998 1/3
Data communication under HP
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
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.
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
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
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.
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.
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.