[Sis-csi] RE: networking details

Fri Feb 9 16:40:06 EST 2007

Ed

Good comments. Add to that the fact that bandwidth becomes more critical
the closer you get to the sensor/effector. VCs were invented to keep the
overhead down. IPv4/v6 pale in comparison when it comes to bandwidth
utilization. Said another way, do you want to use the limited bandwidth
for data or for sophisticated routing mechanisms?

________________________________

From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Edward Greenberg
Sent: Friday, February 09, 2007 3:27 PM
To: Dave Israel
Cc: Keith Hogie; CCSDS Cislunar Space Internetworking WG
Subject: Re: [Sis-csi] RE: networking details

Dave,   You are correct and this stuff that is flying around is just
religious ferver.   I have been trying to get a picture of the in space
networking needs for Constellation for a long time and have yet to see
anything that is operationally blessed.  We can talk about routing
desires for ever but what are the real requirements.  Are things going
to take random walks in space or are missions and hardware movements
going to scheduled and exhaustively tested before anything moves.  Is
automated address management needed, or is it over kill for the first 30
years of the program?    And If the environment in the later years of
the program is centered around the Moon or Mars, how will the delays
effect the operational use of UDP.  Deep space missions have been forced
to use store and forward operations for years, and the protocols
supporting those missions are focus for that environment.  So can anyone
supply an operational scenario that requires the advanced networking
features that IPv6 brings to the table. 

At 2:40 PM -0500 2/9/07, Dave Israel wrote:

	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.

	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 versus
CCSDS" debates, when in reality there really isn't mutually exclusive
decision required?

	Dave

	At 02:20 PM 2/9/2007, Keith Hogie wrote:

	Adrian,

	  A major concern is what you mentioned below about Virtual
Channels.
	Those are a CCSDS data format that was developed 20 years ago
and was
	a fine solution for the time.  It sounds like you are proposing
that
	that VC data structure be maintained as the underlying format
for civil
	space programs for the next 20 years.  Does it make sense to
	plan on extending the life of a 20 year old protocol format for
	20 more years or is it time for an upgrade or replacement of
	the VC format.

	  During the last 20 years lots of protocols have come and gone
and
	been replaced by new ones that better suit users current needs.
The
	commercial world primarily uses Frame Relay and DVB over
thousands of satellite links supporting tens of thousands of users.
They have
	created a very large commercial market of internationally
	interoperable products with much better layering and function
	support than the basic CCSDS VCDU.

	  So it seems that a major question is whether the current VC
	structure is the best structure to use for the future or is it
	time to upgrade to more current solutions at that level?

	  As far as future IP missions interoperating with future
missions
	that see no need for IP, that's fine but then they don't have
any
	plans to communicate with future IP missions anyway.  Ground
stations
	can still support both IP and non-IP formats as many do already.
	The facilities, antennas, transmitters, and receivers still need
	to do their jobs just the same.  The real question is whether
the
	bits coming off the space link go into a CCSDS specific box that
	processes VCs or if the bits go into a commercial router.  This
	is not a major change to the infrastructure.  Yes, it is a
change,
	but the communication world has changed drastically over the
last
	20 years and we need to decide if it is time for the civil space
	community to catch up or if it wants to keep doing its own
thing.

	Keith

	Adrian J. Hooke wrote:

	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:
	1. We can see future requirements for the emergence of a more
networked approach to space communications.

		2. Accordingly, we need to develop a migration strategy
that leads us towards more capable networking protocols.
		3. IP has a role in that migration strategy.
		Beyond those elements of consensus, it's not clear that
there is much agreement on how or when to initiate change.
		At 06:09 AM 2/8/2007, Keith Hogie wrote:

		  Moving to spacecraft using Internet protocols a change
to the whole space communication concept.

		snip

			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.

			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?
			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.

----------------------------------------------------------------------
		  Keith Hogie                   e-mail:
Keith.Hogie at gsfc.nasa.gov
		  Computer Sciences Corp.       office: 301-794-2999
fax: 301-794-9480
		  7700 Hubble Dr.
		  Lanham-Seabrook, MD 20706  USA        301-286-3203 @
NASA/Goddard

----------------------------------------------------------------------

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	______________________________________________________________
	Dave Israel
	Leader, Advanced Technology Development Group
	Microwave & Communication Systems Branch
	NASA Goddard Space Flight Center  Code 567.3
	Greenbelt, MD 20771
	Phone: (301) 286-5294      Fax:   (301) 286-1769
	E-mail: dave.israel at nasa.gov

	"Without deviation from the norm, progress is not possible."
-Frank Zappa

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