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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: GIS/SCADA |
| Date: |
08/09/2002 06:55:10 AM |
| From: |
GS.Rao .. lntinfotech.com |
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Listers,
Here is some additional information on why our customer
(Bombay Municipal Corporation) chose the VSAT way.
To begin with, there were several prerequisites, of which two were
sacrosanct.
Reliability (minimal communication downtime and integrity of data transfer)
and security (transmissions should not be "tapped" ).
The first option that was considered was wireless Radio Frequency.
The only advantage this offered was low cost, even after factoring in the
expense of setting up
booster stations and erecting towers.
The downside was data integrity. Tests showed too much of "cackle".
Filtering out this
noise called for additional equipment at the receiving end, which did not
always succeed
in cleansing the signal.
Another problem was interference. The pipelines mostly run along edges of
roads, along with
their other utility brethren - power, telephone and of late Optical Fibre
cables. The main culprit was the overhead
power cables, which caused a degraded RF signal at source itself.
Not to mention, endemic I suppose to all such situations, the plethora of
regulatory bodies
who have to grant approvals for use of RF.
And, of course, the ease with which RF transmissions can be tapped.
CellularGSM technology was also considered. This option was discarded
mainly because two of the
reservoirs, which were the main source of supply, are located well outside
the city limits, with
no supporting cell network.
VSAT's main drawback was high cost and the excessive unutilized bandwidth.
(more on this later - see scalability).
The main attraction was the "one-stop-shop" option made available by the
local
affiliate of a reputed global telecom operator. They already had
transponders allocated
to them, approved by Govt. of India, with a license to assign frequencies
to their customers.
Their hub, located in India, was manned 24/365 thus ensuring negligible
levels of downtime.
Signals received were bereft of noise. And the time lapse from start to
finish was of the order of seconds.
Also, the whole system was reasonably immune to vagaries of nature
(thunderstorms etc).
Scalability was another great benefit. The BMC intends to install VSAT dish
antennae at all
valve locations along the entire network. This is where the excess
bandwidth would be utilized.
There is also some discussion of their entire computer network being
"ported" to VSAT.
In summary, the long term benefits justified the initial expense. The major
risk here is, if the installation
of antennae over the entire network is delayed. This would erode the ROI.
Cheers
Dr. G. S. Rao
Assistant General Manager - GIS
L&T Infotech Limited
Mumbai, India
G.S. Rao in the previous posting used VSAT (minimum bandwidth 64 Kb) for
the Mumbai water control project, it was probably a pre-existing system to
which he could add a bit of traffic. I would bet that the same data
transfer could have been done with small data messages on Orbcomm rather
than this wide bandwidth / high cost alternative. India lacks a
downloading Gateway and traffic would have had to be in "store-and-forward"
mode, which would have added 1/2 to 1 hour of report delay. There are a
variety of methods to hyper-compress specialized SCADA / positioning / data
report traffic which bring the low-cost & small bandwidth satellite
communicators into many reporting / command / control applications.
Pat
Thos. E. Waggaman, III (Pat)
Director
Marine Imaging Systems S.A.
Ave Borgo=F1o 22.090
Caleta Higuerillas
Vina del Mar
Chile
waggaman@marimsys.com
Tel: 56 32 815005
FAX: 56 32 815243
http://www.marimsys.com
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