[Sis-csi] RE: networking details
Keith Hogie
Keith.Hogie at gsfc.nasa.gov
Fri Feb 9 15:48:44 EST 2007
Dave,
This is not about "IP vs CCSDS". That is comparing apples and
oranges. IP is a network protocol that is independent of the links
it runs over. CCSDS is about link level multiplexing and does not
have network addresses that uniquely identify two end systems.
The reason the link layer matters is that it gets implemented in
hardware on flight systems. Once it is built and on orbit, it cannot
be "optimized" in the future. The ground systems must continue to
support the flight systems link formats for many years.
I agree that getting networking accepted is another issue but it's
easier for new users to accept it if it is done using standard
approaches and mass market products that the network community is
familiar with. The number of vendors producing CCSDS products and
the number of users using CCSDS protocols is very small community.
The question is whether it is best for this small community to
keep maintaining its own link mechanisms ( VCs) or if it is
better to migrate to link mechanisms (Frame Relay, DVB, etc.) that
are used and supported by a much, much larger community.
Howie,
Yes, IP is even more antiquated that VCs, but it has a user
community of 1,093,529,692 users as of Jan. 11, 2007. If CCSDS
had a user community of 1/1000th of that there would be no issue.
But the CCSDS community is extremely small compared to that.
Also, the very large Internet community has decided that IPv4
is antiquated and even with their huge installed base, they
have set themselves on an upgrade path for the next 20 years
with IPv6. Everyone in the communication world moves forward
with new protocols. What are CCSDS's plans for the next 20
years.
Keith
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
>
--
----------------------------------------------------------------------
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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