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Fibre versus Starlink Discussion

Discussion in 'SpaceX' started by banned-66611, Dec 7, 2020.

  1. bxr140

    bxr140 Active Member

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    The point was that "blockage" and degradation from rain fade are not he same thing.
    I can appreciate that message wasn't crystal clear.

    Yes, GEO satellite service in the past was materially different than current generation. To wit "electric cars are crap because they have limited range and no charging infrastructure" was once a valid statement.
     
  2. SageBrush

    SageBrush REJECT Fascism

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    Hi folks,
    Noob with dumb question:

    When a Starlink Sat beams a stream of data to Earth, what is the maximum area on Earth that can receive that stream ?
    Is it a cone or a line ?
     
  3. bxr140

    bxr140 Active Member

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    #163 bxr140, Mar 4, 2021 at 10:16 AM
    Last edited: Mar 4, 2021 at 10:24 AM
    It is more or less broadcast as a cone, and when projected onto the earth at an angle--which is the case except for the instant the cone is directly overhead the user-- the pattern becomes a sort of egg shaped ellipse, with the width and height of the egg being a function of the angle between the satellite and the region on the ground.

    Edit: The user beam width is 1.5°, which translates to a ~150km^2 circle when directly overhead, and probably ~2x that (in an egg shape) at the edge of coverage.
     
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  4. dkemme

    dkemme Supporting Member

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    So a little under 4.5 mi radius?
     
  5. bxr140

    bxr140 Active Member

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    In Freedom Units, yeah. At least when a sat ~directly overhead. Then the beams stretch as the slant angle grows.

    I don't know if there's an image representing starlink out there anywhere, but just for the visual, here's the beam map for the three new Viasats. You can see how the beams progressively cover more area on the ground as the angle between the user and sats grows. The stretching here is to serve extremely low user angles (like, single digit degrees). Starlink user elevations are I think in the 20's or something as a minimum (maybe even planned to be higher?), so the geometry doesn't result in quite the extreme difference in ground coverage from directly overhead to edge of coverage.

    [​IMG]
     
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  6. SageBrush

    SageBrush REJECT Fascism

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    Interesting -- thanks !

    Then if a sat is broadcasting a show in real time, does that mean that anybody with a dish in the coverage area can watch, analogous to broadcast TV ?

    Fwiw, I was reading about the Starlink data capacity ( some 20 gbps per sat) and started to think that all the ways we have to compress, split and join data makes the actual data capacity much, much greater. Not to mention a moving target to innovation.
     
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  7. bxr140

    bxr140 Active Member

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    No. Its still, in layperson terms, the internet. Its just secure data packets. To wit, the only person that knows you're streaming Bridgerton right now is you and the Netflix Mothership.
     
  8. SageBrush

    SageBrush REJECT Fascism

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    Ahh..

    If I am understanding you, every dish in the coverage area receives the packet but only one dish router opens the packet ?
     
  9. bxr140

    bxr140 Active Member

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    Essentially, yeah. A pretty reasonable analogy would be data to/from your device relative to other devices in your same wireless coverage area. Near as I know Starlink is going to use a more proprietary waveform/protocol than whatever a mobile carrier or wifi uses, though I don't really think that changes the analogy much.
     
  10. SageBrush

    SageBrush REJECT Fascism

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    Then without turning the Internet protocol on it's head, could starlink broadcast packets that were 'opened' ** by more than one router ?

    ** I sort of know that the actual mechanism is the IP mask, but 'opened' is hopefully a good enough albeit inaccurate description
     
  11. hmcgregoraz

    hmcgregoraz Member

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    At Layer 3 (TCP/IP) there are things such as broadcast and multicast, but I don't know if SpaceX's Layer 2 would work with this or not.

    Years ago we used to try and leverage multicast for data we knew multiple systems needed (Such as pushing out a system image to a computer lab worth of computers), and there are other protocols to help with this like IGMP (IP multicast).

    In reality today, it has been found that even for streaming services, unicast is generally easier to do and more practical.

    Ie not everyone starts the NetFlix movie at the exact same time.

    At some point SpaceX may decide that a large amount of NAND flash would be worth it to put a Content Delivery Network cache on each StarLink Satellite, but that is probably a fair ways away.

    -Harry
     
  12. Cosmacelf

    Cosmacelf Well-Known Member

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    Starlink uses a proprietary protocol when pushing bits up and down the satellite links to conserve bandwidth. They compress and then reconstruct the TCP/UDP and IP frames at the end points, so it looks like a single hop IP network to us. Also, I believe all Starlink satellite traffic has an encryption overlay onto all the data transmitted.

    And yes, intuitively, you'd think multicast multimedia would be a huge bandwidth saver, but it has never caught on. Partially as hmcgregoraz pointed out, everyone's stream is slightly out of sync anyways due to pauses, rewinds, FF, etc. So two other things had to happen to make it work.

    One is that access networks (the "last mile" from an active central office) had to get upgraded so that enough people could simultaneously grab different streams. This usually means pushing fiber deeper and deeper into the access network, the end result being an all fiber network.

    The second thing is that caching content servers had to be deployed to the network's edge. Large ISPs that serve metro areas all have Netflix and other content cache servers in their distribution hubs, so they only need to grab one copy of the hottest videos that are being watched right now in each 50,000 or 200,000 population user area.
     
  13. SageBrush

    SageBrush REJECT Fascism

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    Multicasting.

    I admit it, Netflix was the scenario I was contemplating ;)

    Not starting at the same time ... but more along these lines of the same movie:

    1. Movie download started at 10:00 pm by home #1: Sat starts broadcast
    2. Movie started at 10:10 by home #2: Both homes receive movie from 10:10. Home #1 views in Sat real time, Home #3 caches. Home #3 downloads in a separate stream the first 10 minutes
    And you are right -- nothing stopping us from thinking about predictive multi-cast downloads.
     
  14. hmcgregoraz

    hmcgregoraz Member

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    The kind of edge caching that would be needed for that (ie integrated in to the CPE/Router/etc) is kinda interesting. I actually am a co-inventor on a patent that covers that kind of technology and predictive analytics tied to it.

    That being said, most IP networks have just gone the "more bandwidth" route, and SpaceX really is not any different, they are doing it with more satellites....

    -Harry
     
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  15. MorrisonHiker

    MorrisonHiker S 100D 2021.4.11

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    20 years ago, Primestar, DIRECTV and DISH all had PPV offerings where they would schedule a movie to start every 30 minutes or so. You could buy it and it would enable you to view the broadcast that was already in progress or watch an upcoming broadcast of the movie. This used a lot less bandwidth than using a different stream for each viewer but it wasn't nearly as viewer-friendly as instantly streaming movies to each viewer.

    Eventually, DIRECTV and DISH offered boxes with hard drives and they would automatically download a few of the most recent movies to them. This way you could start a movie whenever you liked, but the selection was pretty limited.
     
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  16. SageBrush

    SageBrush REJECT Fascism

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    Unless they decide to compete in dense urban areas ...
     
  17. SageBrush

    SageBrush REJECT Fascism

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    These posts confirm at least the future possibility of Starlink having much more practical bandwidth than 20 gbps * viewable_sat_number would suggest

     
  18. drtimhill

    drtimhill Active Member

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    There is no "good" solution for rural broadband since by definition the low household density makes physical connectivity (e.g. fibre/fiber) prohibitively expensive, and any shared non-physical solution (wireless of any sort) will always eventually suffer congestion issues. A service like Starlink changes the overall balance since it can address area that are poorly serviced even by cell phone services.
     

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