On Sun, Feb 25, 2018 at 3:14 PM, Poutnik <[email protected]> wrote: > Using analog repeaters would be very dumb thing to do and would not > work well. > There is no need of msg processing for the digital repeaters, e.g. like > in the ethernet network.
https://en.wikipedia.org/wiki/Globalstar#System_architecture > Globalstar satellites are simple "bent pipe" analog repeaters, unlike Iridium. Analog repeaters are used aboard spacecraft more than you might imagine. Certainly in the early 2000s (and maybe even today, I've moved on from the job of maintaining TV systems and haven't kept up) the TV network distribution satellites were all analog repeaters. They carried digital signals, but the bird didn't need to know that. (At the time, one project I worked on was converting the system from CCIR-601 to MPEG-2.) Most of the 'security' came from the fact that the uplinks in New York had extremely powerful transmitters (multiple kilowatts in L band, at least hundreds of watts in Ku band) and could simply outshout any would-be jammers. I'm guessing that the system doesn't work that differently today - some of the spacecraft that the people rented then are still in service now - years past their projected operating life. The system that the company I worked for used was maintained by GE Americom - now SES S.A. One advantage of analog is that you don't need to change anything on the spacecraft in order to change protocol entirely. The spacecraft often outlast the transmission protocols (OK, IP is long lived, but some of the application protocols on top of it are pretty volatile.) Keeping them dumb can be smarter than you'd imagine. In any case, most of the ones that I've worked with never demodulate the signal. They just shift frequency or polarization and send it on its way. It might not be how you or I would design it, but it flies. > The above does not say it does not use internet protocol suite from the network layer above. And, in fact, I was wrong in asserting that it's SMS; it's only "SMS-like." (I think I had SPOT confused with InReach.) It's proprietary, but it's been pretty comprehensively decoded and compromised; there's a Black Hat presentation about it at https://www.blackhat.com/docs/us-15/materials/us-15-Moore-Spread-Spectrum-Satcom-Hacking-Attacking-The-GlobalStar-Simplex-Data-Service.pdf The last few slides are devoted to the packet format - this is the link-layer packet, not any transport- or presentation-layer protocol. It really, truly is that simpleminded. -- You received this message because you are subscribed to the Google Groups "Osmand" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
