Keith,
It seems that I must correct myself regarding your message
of June 26th...
While I stand by my previous comments, they missed the point that
(it is now clear) you were making:
Envisat's DDS (*NOT* the Envisat platform itself) is an excellent
example of proper use of UDP/IP by a space mission.
(The point I missed: The Envisat spacecraft itself is not using
UDP/IP - or even DVB)
To this, I fully agree - and apologize for missing it the first
few times around.
To further discuss, the following elements of your message:
Keith Hogie wrote:
<snip>
> What we see for missions using IP is a very heavy use of UDP and not
> TCP.
<snip>
> For an example of other UDP use see the following:
>
> http://www.esa.int/export/esaCP/ESALS5OED2D_index_0.html
> http://www.gcs-salzburg.at/
> http://www.gcs-salzburg.at/products/p_odg.html
> http://www.simple.at/
> http://www.datacast.at/technology.html
<snip>
> The bottom line is we want to use standard IP/UDP/TCP protocols that
> are supported in every operating system available. Using a modified
> TCP requires more software support that creates more problems when
> you are building and deploying operational control centers and
> level-zero processing systems. We really prefer to use standard
> protocols at layer 4 and below and do any space specific tweaks
> in the application layer.
coupled with the context of the discussion that prompted your message - the
use of TCP by spacecraft elements - lead me (and perhaps a few others) to
totally misinterpret the actual significance of the ESA press release (and
product information) links that you provided.
Sometimes we read what we want to see :o)
The unfortunate result of this is that:
The inclusion of Envisat as an example of a space based sensor
platform using of IP is not quite an accurate portrayal of how
the Envisat data is actually being disseminated...
As the press release (and associated product links) so clearly state,
the mission data *is* indeed disseminated to subscribers via multicast
UDP/IP/DVB but this is only *after* the Envisat delivers the data to the
ground non-IP related mechanisms;
The Envisat spacecraft itself does not appear to be using DVB or IP,
Envisat seems to be only using CCSDS link protocols (probably nothing
more at layers 3 or above):
http://ccsds.gst.com/implementations/missions.html (mission 98)
and
http://esapub.esrin.esa.it/pff/pffv6n4/polv6n4.htm
Envisat's DDS (Data Dissemination System) is what so successfully exploits
commercial communication satellite(s) and DVB encapsulation to redistribute
the data.
http://esapub.esrin.esa.it/bulletin/bullet109/badessi.pdf
This is more than slightly different from Envisat itself using
multicast IP. Again, I misread the significance of the press release
you were providing.
What Envisat does illustrate so well to this community is an extremely
pragmatic way of doing business:
(1) Delivering science products efficiently, reliability to
the ground
(2) Disseminating that data to the user community via IP-based
networks
(*) Envisat is *not* the only/first mission to do this, but their
data volume is truly impressive!
The end-result is that this approach allows for the subscriber community
to receive their data using "vanilla" (non-space tweaked) IP-based networking
technology and the method of communication to/from the spacecraft is of no
consequence to them.
Kudos to ESA for an excellent (high profile) illustration of how to exploit
IP technology for the distribution of space science data.
Space missions have been doing this sort of thing for some time - and should
continue to do so.
Eric
This archive was generated by hypermail 2b29 : Fri Jul 05 2002 - 14:23:39 EDT