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| | Meteosat-8/9 Data Flow
- Data is transmitted from the Meteosat-8/9 (MSG-1/2) spacecraft down to Earth
stations in Germany.
- That data is refined, compressed and encoded as HRIT and
LRIT files.
- The HRIT and LRIT files are added to the EUMETCast service
- The EUMETCast data is sent up to the Eurobird-9 satellite in
small packets of data.
- Other packets of data, such as Foreign Satellite Data
(FSD), Rapid Scanning Service (RSS), ATOVS and EARS files, are
also sent up to Eurobird-9, but with different packet identifiers (PIDs).
- Your dish, LNB, and Skystar2 card receive the packets of
data.
- The Server4PC turns the data packets into a TCP/IP stream,
passing only the PIDs you have selected.
- The T-Systems TelliCast software recovers the files
from the TCP/IP stream, looking only at the data channel names you have selected.
- The MSG Data Manager software turns the files into
images.
- The MSG Animator
software provides quick-look, real-time animations
- The GeoSatSignal software turns the
images into multi-channel, false-colour, remapped animations.
My PC Configuration
Reception
PC
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Processing
PC
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TelliCast
software |
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MSG Data
Manager software |
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MSG
Animator software |
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GeoSatSignal
Software |
Server4PC |
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SkyStar2 drivers |
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Windows
XP Home
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Windows
XP Pro
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Processes
HRIT & LRIT files from reception PC into images |
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Processes
images into real-time animations |
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Processes
images into multi-channel, false-colour, rectified animations |
DVB
card |
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Network card |
Network card |
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| Dish and LNB |
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Network Hub
provides 100Mb/s connection |
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What does the DVB card and its software do?
Based on tests we needed to do for Windows Vista, my
understanding of what happens between the DVB card and the TelliCast software
has increased a little.
There is a network device driver named SKYnet.sys, DVBnet.sys
(or similar) which provides the network interface. As far as the operating
system is concerned, this is a network driver and it is the device to which you
assign the address 192.168.238.238. It therefore appears capable of
talking to other devices or networks connected to the virtual LAN adapter on
that address. The PC thinks it has two network cards, and needs to decide
which one to use to talk to any external connection, and this has implications
for Windows Vista.
The software associated with the SkyStar2 card or USB box you
are using talks to the device driver, converting packets received from the
satellite from DVB packets to Internet packets. Each DVB packet has a
packet identifier (PID), which associates it with a particular hardware
origination address (the MAC address). Within each PID, there can be one
or more data streams (such as Metop data, HRIT data etc.) By some process
which I do not currently understand, each stream will appear to originate
from a particular fixed network address such as 224.223.222.223. I guess
this information is carried in the announcements of the data, but how you you
know the address of the announcement channel?
So the job of the DVB software and network device driver is to
turn a stream of DVB packets from a particular PID, into one or more IP data
streams which appear to originate from a particular IP address. What does
the TelliCast software do?
The TelliCast software has a number of functions, some of
which I understand better than others!
- As the DVB packets come in, the required PIDs are selected
by the hardware in the DVB card or USB box.
- Following that filtering, the packets are converted from
DVB format to IP format, and given a particular source address.
- When a new set of packets for a source address appears,
TelliCast is given the chance to register an interest, and request a
connection.
- For each source address, if the TelliCast software has
requested the data, the IP format packets are sent to the DVB network
software.
- The DVB network software makes the packets appear to have
come from a real network adapter, and sends them to the operating system.
- The TelliCast software picks up those packets from the operating
system via standard network I/O calls.
- TelliCast performs some error detection and correction.
- TelliCast stores the file fragments in a local buffer, or
on disk in the FSY file.
- Finally, TelliCast assembles complete files from the
incoming and/or saved packets.
In more detail:
- When the TelliCast software starts, it must establish a
connection to the DVB network software on 192.168.238.238. While this
connection is being established, the yellow icon is displayed. If the
connection fails, a red icon is displayed, and if it succeeds, a
"pink" icon is displayed. This requires the ability of the
program to connect outwards, and a firewall entry may be required to allow
this to happen.
- Somehow the software registers an interest in UDP data from
the DVB network.
- It then needs to connect to the "Announcement"
channel, which has an address of: 224.223.222.223:4711. The name and
address of this channel are defined in the recv.ini file.
- When a new set of files are ready to be sent over
EUMETCast, a message is sent to the announcement channel, and hence to the
TelliCast software. The TelliCast software will check whether the user
wants this data (by checking the entries in the recv-channels.ini file), and
whether the user is authorised for this data. If the data is wanted
and authorised, the TelliCast software will try and make a connection with
the DVB network software so that the following UDP data is sent to the
TelliCast application.
I am sure that a large part of this is setting up and using a
standard UDP data transaction, but I still have to find a good description of
that on the Internet.
More information and images
Automated system monitoring tools
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