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Before another whole thread starts about link layer issues again, can
somebody explain why the link layer matters are so critical at this time
that we keep spending time and energy debating them, instead of working
on the many networking issues that need to be resolved? I'd rather
see that discussed, than any arguments about any link protocols.<br><br>
It seems to me that the real need is to get missions to start evolving to
networking based communications first. Once that starts,
optimization may follow. How much time have we lost in "IP
<i>versus</i> CCSDS" debates, when in reality there really isn't
mutually exclusive decision required?<br><br>
Dave<br><br>
At 02:20 PM 2/9/2007, Keith Hogie wrote:<br>
<blockquote type=cite class=cite cite="">Adrian,<br><br>
A major concern is what you mentioned below about Virtual
Channels.<br>
Those are a CCSDS data format that was developed 20 years ago and
was<br>
a fine solution for the time. It sounds like you are proposing
that<br>
that VC data structure be maintained as the underlying format for
civil<br>
space programs for the next 20 years. Does it make sense to<br>
plan on extending the life of a 20 year old protocol format for<br>
20 more years or is it time for an upgrade or replacement of<br>
the VC format.<br><br>
During the last 20 years lots of protocols have come and gone
and<br>
been replaced by new ones that better suit users current needs.
The<br>
commercial world primarily uses Frame Relay and DVB over thousands of
satellite links supporting tens of thousands of users. They
have<br>
created a very large commercial market of internationally<br>
interoperable products with much better layering and function<br>
support than the basic CCSDS VCDU.<br><br>
So it seems that a major question is whether the current VC<br>
structure is the best structure to use for the future or is it<br>
time to upgrade to more current solutions at that level?<br><br>
As far as future IP missions interoperating with future
missions<br>
that see no need for IP, that's fine but then they don't have any<br>
plans to communicate with future IP missions anyway. Ground
stations<br>
can still support both IP and non-IP formats as many do already.<br>
The facilities, antennas, transmitters, and receivers still need<br>
to do their jobs just the same. The real question is whether
the<br>
bits coming off the space link go into a CCSDS specific box that<br>
processes VCs or if the bits go into a commercial router. This<br>
is not a major change to the infrastructure. Yes, it is a
change,<br>
but the communication world has changed drastically over the last<br>
20 years and we need to decide if it is time for the civil space<br>
community to catch up or if it wants to keep doing its own
thing.<br><br>
Keith<br><br>
<br>
Adrian J. Hooke wrote:<br>
<blockquote type=cite class=cite cite="">Maybe this is a good time to
take stock of where we are. I think that it is fair to say that there is
broad international agreement that:<br>
1. We can see future requirements for the emergence of a more networked
approach to space communications.<br>
2. Accordingly, we need to develop a migration strategy that leads us
towards more capable networking protocols.<br>
3. IP has a role in that migration strategy.<br>
Beyond those elements of consensus, it's not clear that there is much
agreement on how or when to initiate change.<br>
At 06:09 AM 2/8/2007, Keith Hogie wrote:<br>
<blockquote type=cite class=cite cite=""> Moving to spacecraft
using Internet protocols a change to the whole space communication
concept. </blockquote></blockquote><br>
snip<br><br>
<blockquote type=cite class=cite cite="">
<blockquote type=cite class=cite cite="">If we start launching some of
our future systems with no routed IP, is there a clean path for them to
"migrate" and be full participants in the future network.
</blockquote>Turn that around. If we start launching *some* of our future
systems exclusively with routed IP, is there a clean path for them to be
full participants in the future international community of missions that
see no need for it?<br>
Nobody's arguing that there won't be an increasing need for portions of
the international space mission support infrastructure to adopt more
powerful routing technologies. When you need IP and IP works, you should
use IP. But does that mean that *everything* has to become IP-based, all
at once? And yes, there's a migration path: it's called international
space standardization in general and in particular it's called a Virtual
Channel. It means that you can run part of your system using existing
infrastructure, in parallel with part of your system using IP-based
approaches. Change the mix of traffic on the VCs and you can migrate with
hardly any impact.<br>
</blockquote><br>
----------------------------------------------------------------------<br>
Keith
Hogie
e-mail: Keith.Hogie@gsfc.nasa.gov<br>
Computer Sciences Corp.
office: 301-794-2999 fax: 301-794-9480<br>
7700 Hubble Dr.<br>
Lanham-Seabrook, MD 20706
USA 301-286-3203 @
NASA/Goddard<br>
----------------------------------------------------------------------<br>
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</blockquote>
<x-sigsep><p></x-sigsep>
______________________________________________________________<br>
Dave Israel<br>
Leader, Advanced Technology Development Group<br>
Microwave & Communication Systems Branch<br>
NASA Goddard Space Flight Center Code 567.3<br>
Greenbelt, MD 20771<br>
Phone: (301) 286-5294 Fax:
(301) 286-1769<br>
E-mail: dave.israel@nasa.gov<br><br>
"Without deviation from the norm, progress is not
possible." -Frank Zappa</body>
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