Network topology design at 27,000 km/hr • Hacker News Board

Re: Network topology design at 27,000 km/hr

#11

Post by sriku » Sat, Feb 29, 2020, 8:38 AM UTC

While general purpose satellite internet is nice, I'm wondering (in brainstorm mode) about whether there are alternative situations for which an architecture based on such fast moving satellites would be desirable rather than a challenge.

Below are some unfiltered thoughts on this -

1. Treat satellites like postboxes. If ground to satellite link is fast, use it to upload TB of data to these satellites and let them transport it across oceans and dump them at destinations (article notes it takes 6mins to cross the Atlantic).

2. Serve applications off satellites - sort of like CDN edge servers. Thinking Cloudflare Workers. No idea what their capacities are though.

3. Distribute updates to devices or end points. Tesla updates?

4. Make the satellites pick up and drop data between specific ground stations.

Any intelligent ways to abuse this system?

Re: Network topology design at 27,000 km/hr

#12

Post by mhandley » Sat, Feb 29, 2020, 11:24 AM UTC

erentz wrote: post #7

walrus01 wrote: post #5

The first generations of Starlink satellites will serve as bent pipes. They're not doing intersatellite links. This will require dozens of small trunk-link earth stations around the USA, in the same general region for rural services. For example an earth station near the fiber in Boise, ID would have visibility for bent-pipe type relay to the same satellites presently overhead of many very hard to reach, rural, remot…

That’s really disappointing to learn. It was the inter-satellite linking part that make it really interesting (to me) and which promised to provide big latency improvements over fiber (over longer distances). I wonder if it proved too hard in practice?

Elon Musk has stated that until they have inter-satellite laser links deployed, they can get wide area low latency communications by relaying via ground stations at a high slant angle. I built a simulator and ran an analysis of this, and actually it works pretty well. My video analysing all this is here: https://youtu.be/m05abdGSOxY

Re: Network topology design at 27,000 km/hr

#13

Post by walrus01 » Sat, Feb 29, 2020, 12:08 PM UTC

mhandley wrote: post #12

erentz wrote: post #7

Earlier quoted context omitted.

That’s really disappointing to learn. It was the inter-satellite linking part that make it really interesting (to me) and which promised to provide big latency improvements over fiber (over longer distances). I wonder if it proved too hard in practice?

Elon Musk has stated that until they have inter-satellite laser links deployed, they can get wide area low latency communications by relaying via ground stations at a high slant angle. I built a simulator and ran an analysis of this, and actually it works pretty well. My video analysing all this is here: https://youtu.be/m05abdGSOxY

There's a variety of software packages you can use to simulate the ground footprint of a starlink satellite, from the TLEs (two line elements). Or Iridium or anything else.

It's a circle many hundreds of km wide. Assuming that an earth station will have a minimum look angle of about 18 degrees above the horizon, one can calculate the serviceable area for customer and trunk link spot beams within the satellite's moving footprint.

The scenario shown in your youtube video has uses for HFT and similar very latency sensitive applications. But because it's RF, there's no way that a chain of starlink satellites relaying through multiple ground stations will compete in raw throughput and capacity with fiber. Remember that a single IT standard 100GHz grid DWDM channel is a few terahertz wide, and 80 channels can easily fit in the conventional bands of a long haul DWDM system in just two strands of fiber.

Re: Network topology design at 27,000 km/hr

#14

Post by mhandley » Sat, Feb 29, 2020, 12:14 PM UTC

walrus01 wrote: post #13

mhandley wrote: post #12

Earlier quoted context omitted.

Elon Musk has stated that until they have inter-satellite laser links deployed, they can get wide area low latency communications by relaying via ground stations at a high slant angle. I built a simulator and ran an analysis of this, and actually it works pretty well. My video analysing all this is here: https://youtu.be/m05abdGSOxY

There's a variety of software packages you can use to simulate the ground footprint of a starlink satellite, from the TLEs (two line elements). Or Iridium or anything else. It's a circle many hundreds of km wide. Assuming that an earth station will have a minimum look angle of about 18 degrees above the horizon, one can calculate the serviceable area for customer and trunk link spot beams within the satellite's movin…

Yes, that's correct, but the interesting part is not the footprint, but the latency and variability of the dynamically routed paths you can obtain. That's what I simulated. I also made some modifications to how you'd normally route such a network, because the conventional approach wasn't fast enough if you have a wide choice of groundstations and the topology is continuously changing. The animations in the video are doing the route calculations in realtime once per frame of video; I was pretty pleased with those optimizations. One surprise, for me at least, was that there are paths where you sometimes want to relay via ground stations, even when the satellites have inter-satellite laser links. That's in the video towards the end.

Edit: in response to the point you added about bandwidth: that's correct - there's no way the ground relay path competes with fibre on bandwidth. There are, however, many potential uses that require low latency and are not high bandwidth.