[Sis-csi] RE: networking details

Thu Feb 8 15:14:47 EST 2007

>From an industrial process control systems perspective, IP is used at
the supervisory level, but not at the control level. The reasoning is
clear. First, control systems have limited interconnectivity - just
enough to do its job. Second, control systems don't want external
communcations to have the potential for disrupting control. Therefore,
gateways are used connect control networks to supervisory networks. In
reality, there is usually more than one layer of supervisory networks,
isolated from each other by gateways. For cost reasons, almost all
supervisory networks use IP, but with private subnet addresses. Private
subnet addresses ensure that there are no unregulated cross network
traffic flows.

________________________________

From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Assi Friedman
Sent: Thursday, February 08, 2007 2:04 PM
To: 'Adrian J. Hooke'; 'CCSDS Cislunar Space Internetworking WG'
Subject: RE: [Sis-csi] RE: networking details

I would like to point out that a lot of discussion needs to go into the
physical/link layers of this migration. CCSDS as-is is has its history
significantly influenced from the STDN era. This history does not make
it very conducive to IP in space. Migrating to IP will require us to
address the physical/link layers. As is, CCSDS had the foresight to
acknowledge that there will be a future need to readdress this, but the
future is now present. I try to start at the side closest to the
hardware, since protocol stacks can be reloaded, hardware boxes are much
harder to reload.

Assi

**************************** 
 Assi Friedman - Innoflight Inc. 
 5850 Oberlin Dr. Suite 340 
 San Diego, CA 92121 
 Tel: (858) 638-1580 X13 
 Fax: (858) 638-1581 
 Email: afriedman at innoflight.com 
**************************** 

________________________________

From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Adrian J. Hooke
Sent: Thursday, February 08, 2007 11:34 AM
To: CCSDS Cislunar Space Internetworking WG
Subject: Re: [Sis-csi] RE: networking details

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.  

No, it's not a change to the space communication *concept*; it's a
change to the space communication *infrastructure*. If we go there in
one big bang, it will certainly change a lot of infrastructure. But is
it change for the sake of change, or change because we simply can't
operate another day in space without an all-IP system?

Now we are changing the space end so that selected Internet technologies
and be used end-to-end.

Why? There are plenty of cases where selected use of Internet
technologies is beneficial *without* using them end-to-end.

If we accept that we want and need a routed infrastructure in space in
the future, why wouldn't we want to start putting it in place with
missions currently being built. 

Well, cost ands risk *might* be among the reasons. Why do the NASA
Exploration vehicles currently being built look so much like Apollo?

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.

Isn't it more beneficial to take this opportunity to deploy a whole
fleet of new systems and start the first systems with the technologies
we want to end up with.

This far out, how do you know where you will end up? Isn't it more
beneficial to take the opportunity to deploy new systems that are based
on the technologies that we use now, which already have the built-in
capability to evolve towards IP or any other future routed approach? 

Starting new missions with IP technologies also means that they can
start benefiting from the greatly increased options for early testing
between various subsystems. Systems don't need to wait until final
integration and test to start doing interoperability tests.  With IP
interfaces built in, systems can start running basic interface and
functionality tests while they are still at their manufacturing
locations.  This can be done years earlier than normal I&T and find
basic problems much earlier when they are easier and cheaper to fix. 

This claim is so sweeping that it deserves its own discussion thread.
Suffice to say that there are many people on this list who strongly
doubt that the impacts on the real world of space mission I&T are
anywhere near that rosy.

I agree that we don't need to pin down all the details now, but we do
need to have some sort of plan on how things will roll out.  

We all agree with that.

We may not need all the network routing capabilities for 10 years but
there seem to be lots of benefits from starting to make use of
end-to-end Internet technologies now.

Of course: that's why we formed this Cislunar Space Internetworking
working group. But as an international standardization working group, it
should develop a pragmatic and consensus strategy for how it proposes to
move the international space community forward. We need a clear picture
- agreed by all partners - that shows why we need to change, when we
need to change and how we need to change.

///adrian

Adrian J. Hooke
Chairman, CCSDS Engineering Steering Group (CESG)

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