[e2e] TCP in outer space
cannara at attglobal.net
Wed Apr 11 17:58:11 PDT 2001
Just a few comments...
The Internet as we knew it before IPv4+ was quite parochial in its
design parameters -- no concept of LANs, no concept of vast numbers of
addressible entities, and, especially with TCP, no provision for
performance enhancement over long-delay links with significant physical
loss (not congestion). If anything, the Internet was, and largely still
is, a "dedicated, purpose-built Internet". The purpose being defined
many years ago. And, heavily subsidized to boot.
These issues remain. In a sense, one can judge lack of generality by
the amount of effort needed to bring a design to meet the next level of
demand on it, foreseen or not. IPv6 is an excellent example of huge
efforts, initially directed at one or two areas in which IP was
deficiently designed, that have yielded both forward and backward steps.
All the discussion on ECN, etc. also demonstrates how little thought was
given, over many years, to addressing fundamental networking realities
that have nothing to do with a particular protocol, but a lot to do with
To this, we can also add the extreme lack of attention to security in
the "good enough" IP world, that has demanded, and will continue to
demand, huge expenditures in Internet-protocol redesign and extension (a
charitable assessment). We won't even bring up the costs already
incurred by the historically lackadaisical attention to security in the
Internet's base protocols.
In the realm of huge round-trip delays, with various possibilities for
physical-channel interruption/intrusion, both extended and sporadic, it
is irresponsible not to examine a wide variety of alternatives, treating
the 'sacred' Internet as it should be -- one existence proof of several,
in a limited domain.
"David P. Reed" wrote:
> I hope this isn't boring the vast majority of e2e list participants. (send
> complaints to me, not to the list!)
> But now I'm really intrigued. Here's why: a "space Internet" is (should
> be?) motivated by the same rationale as the original Internet - a network
> of heterogeneous networks can incorporate technological and applications
> innovation much more effectively than dedicated, purpose-built Internet.
> TDRS is a dedicated, highly "optimized" technology (at a point in time, for
> a class of applications). Sounds wonderfully well thought out. But... Like
> all "optimized" technologies, it is brittle with respect to
> change. Doesn't tolerate new infrastructures or new applications very well.
> IP is, as we all know, "good enough" technology, optimized for nothing in
> particular, except for its ability to rapidly incorporate or support new
> stuff at the low levels and new apps and requirements at the high levels.
> Now that there's enough going on in space, I'd say the time is NOW to start
> architecting a "space Internet". Remember, the Internet is not the
> hardware, and never was. You can run "space Internet" over TDRS and
> anything else out there.
> I bet there is a cadre of young designers who can carry this torch, just as
> the young students and others carried the Internet torch. It is clearly
> "enabling" technology for space exploration, and even more than ISS, it can
> enable all kinds of stuff to happen. But the key has to be a net that
> follows design principles like the Internet's. End-to-end, liberal on
> inputs, conservative on outputs, no specialization to underlying transport
> "features", no privileged "applications".
> Comments below.
> At 02:01 PM 4/10/01 -0700, Courtney, Bill wrote:
> >One of the problems with using non-GEO satellites is that
> >the topology of the constellation is changing. True,
> >it changes in a predictable way, but the changes will,
> >nonetheless, require network reconfiguration. With non-GEO
> >satellites, not only might the inter-satellite links
> >be breaking and making, but also the earth-space access
> >links for each user will be continually changing.
> Yup. The fact that links are independent of technology is what makes it a
> "network". In the Internet, we said, since topology is constantly being
> broken because of reliability and autonomy, we need a routing protocol that
> can incorporate change, and a transport protocol that doesn't bind
> end-to-end state into physical circuits.
> >In addition, satellite coverage footprints in a
> >constellation usually overlap, and for many
> >constellations the overlaps are also in constant
> >change. This means that uplink and downlink bandwidth
> >allocations among the satellites will be subject to
> >changing re-use constraints. This makes it difficult
> >to ensure that users in any particular area on the
> >ground will receive a constant amount of bandwidth. And
> >fluctuating access bandwidth leads to all sorts of
> >problems, as you can imagine.
> Fluctuating access bandwidth is no more a problem than fluctuating
> application demand. I suspect that fluctuating app demand is "hidden" in
> low average utilization of end-to-end fixed rate circuits. To me, there
> are very few applications (voice is one) that really have "fixed rate"
> needs. The rest are kludged by assigning a fixed rate circuit that can
> handle worst case traffic, then leaving most of the capacity idle.
> It's hard to believe that computer-computer (and human-human mediated by
> com-puter) traffic is fixed rate. So the matching of demand to capacity by
> buffering and dynamic allocation (e.g. datagrams and bursty VCs) is going
> to be an issue for space - why not admit it and design a network that does
> >These and other difficulties must be balanced against the
> >possibility that latency might be lowered with non-GEO
> >constellations. (I say "might," because some of the
> >non-GEO difficulties can be addressed at the cost
> >adding latency.) Non-GEO can be a bear!!
> It isn't just latency that might be lowered. Like the Internet, by
> allowing the incorporation of a wide variety of underlying technologies,
> new applications can be introduced at low cost. Every time we increase the
> level of resource sharing by creating a network to mediate access to a
> resource (i.e. space), we boost innovation by lowering the cost of entry.
> It would seem to me that a "space Internet" would be as big a deal as the
> "fast, cheap, out-of-control" mars robot design philosophy is.
> Of course, I hold no hope to sell this idea to the "Beltway Space Bandits"
> - the corporate biggies whose goal is to sell expensive engineering time to
> risk-averse gov'ts, rather than looking for ways to do stuff cheaply and
> innovatively. But maybe there's an innovative scientist-type at NASA or JPL?
> - David
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