[Starlink] some details on the DTN, bundle protocol, and a capacity question

[Vint Cerf]

I am a fan of Fountain codes - however, it only works if you have all the
data you are going to send in hand before encoding.
David, if there is a way to do this with data that is being generated on
the fly with sensors, that would be of interest.

Of course, one can "chunk" the data, fountain-code it, and reconstruct
"chunks" on receipt.

v


On Sun, Dec 12, 2021 at 3:39 PM David P. Reed <dpreed at deepplum.com> wrote:

> It's worth noting that the patents on Bill Luby's digital fountain codes,
> etc. have pretty much inhibited one of the best solutions for DTN out
> there. There's one exception - RFC 6330, which has a very, very specific
> use of the RaptorQ code specified in it. Qualcomm apparently negotiated a
> license for that very specific use in that specific protocol, as long as it
> is never used in "wide area wireless" (see the details of the narrow
> license here) networking. https://datatracker.ietf.org/ipr/2554/
>
>
>
> Rateless erasure codes of ANY kind appear to be covered by the claims in
> the early Digital Fountain patents.
>
>
>
> Now why are rateless erasure codes important for DTN? Well, essentially
> such codes have a *unique* property that is pretty surprising:
>
>
>
> The coded form of any N-bit message (composed of segments that can be
> lost, e.g. checksummed frames that are deemed lost/erased if the checksum
> fails), is an infinite sequence of non-identical segments. If a receiver
> receives a subset of distinct segments, totalling N or more bits, the
> entire N-bit message can be reconstructed.
>
>
>
> That's what makes the code "rateless" - it works for ANY error rate, and
> is optimal for that error rate.
>
>
>
> To solve the DTN problem, you simply send each message as a sequence of
> coded segments. No windowing is required, no retransmission of packets that
> are lost on one hop is required. Eventually, the message gets delivered,
> and it will take no more time than the error rate on the path requires.
>
>
>
> That's remarkable.
>
>
>
> There are of course some issues to resolve - when should a message source
> assume that its message has been reliably and completely received by the
> intended destination?
>
> This is the "end-to-end" problem. If there is a reverse channel, once a
> message has been received, the receiver should, at least each time it
> receives a segment of some already completed message, send a single ACK for
> that message.
>
>
>
> Now this is great for talking to a spacecraft that has a very low speed
> and noisy reverse channel.
>
>
>
> Any number of messages can be concurrently sent from any number of sources
> (the requirement is that each message has a global unique ID).
>
>
>
> Fair sharing of a multiplexed deep-space network's resources among many
> concurrent messages is a bit more tricky. That's where "early ACks" might
> be used in an advanced erasure code (one I doubt has been patented fully,
> at least I've never seen that).
>
> -----------------------------------
>
> Now, my personal view about *patents* on communications protocols is very
> severe: since interoperability is the *essence* of communications
> protocols, the idea of patents is antithetical to the utiliity of
> protocols. Just as mathematical algorithms should not be patentable subject
> matter, neither should communications protocols (which are just algorithms
> on a different abstract machine).
>
>
>
> Unfortunately, Luby, et al. have threatened litigation over and over,
> stymieing attempts to get usage of their remarkable invention, outside a
> few monopolistic or oligopolistic licensees.
>
>
>
> It looks like, even though the original patents are due to expire soon,
> lots of effort is being made to insure that all possible derivable
> techniques are being patented to extend this monopoly.
>
>
>
> Consequently, I'd suggest that someone might find a way to "buy out" the
> inventors of these patents and their assignees. It's a cancerous growth.
>
>
>
> Imagine if we who built the Internet Protocols had filed patents on all
> the techniques used in the Internet? Would Vint be sitting there counting
> his royalties, and with a team of lawyers negotiating license agreements?
> (I have an oar in this - I'd be there with Vint in the countinghouse,
> probably, as a coinventor).
>
>
>
> Bill Luby, his advisors, etc. did a remarkable thing here. And like other
> inventors, he ought to be rewarded for his invention. I have no problem
> with that. What I have a problem with is the structure of patent law as it
> exists today. It is socially counterproductive, and economically
> counterproductive, when used in the way it is being used here.
>
>
>
> But that's just my opinion.
>
>
>
> PS: I am co-inventor of a fair number of patented inventions. I live in
> this broken system. But, in the case of communications protocols
> specifically, I think this stuff shouldn't be protected by patent rights.
>
>
>
>
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-- 
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Vint Cerf
1435 Woodhurst Blvd
McLean, VA 22102
703-448-0965

until further notice
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