5 ms·
It gets better. The speed of light in a fiber optic cable is about 2/3rds of C. The proposed system (from what I understand) essentially uses free space optics
by erentz 9y ago
It gets better. The speed of light in a fiber optic cable is about 2/3rds of C. The proposed system (from what I understand) essentially uses free space optics between the constellation of satellites as the backbone. Instead of regular satellite internet service which routes up to a satellite then down to a ground station then over a fiber optic backbone. SpaceX’s system will route traffic across the constellation of satellites then down directly to the remote end (or the closest egress point to whatever the remote end is if they aren’t on the network). This means although total distance travelled is longer, the speed it’s travelling at is 1/3rd faster. So overall this will become very interesting for latency sensitive long distance communications.
- JumpCrisscross 9y ago> the speed it’s travelling at is 1/3rd faster About 50% faster if the speed of light in fibre is 2c/3.
- oh_sigh 9y agoJust did some back of napkin math, and assuming you wanted to transmit information half way across the world with a fiber optic cable at sea level that goes exactly where you want it to, it would go 12566 miles (2pi4000/2) @ 124,666 miles per second (2/3)c, or take ~.1 seconds. If you transmitted data straight up 700 miles, and then around the constellation all at 700 miles elevation, and then back down 700 miles, it would need to go 16165 miles (700*2 + 2pi4700/2) @ 187,000 miles per second (1c), or take 0.086 seconds. This seems like pretty exciting stuff.
- Cerium 9y agoI did the same math, got a similar result. I found that getting data from one side of the earth to the other should be about 17.4% faster in space. Since the earth is 6,378 km in radius, adding another 1,150 km only makes the circumference about 18% longer.
- jacquesm 9y agoYou need to add more latency for every time a device is encountered in the total path. As long as the amplifiers are optical that's a non issue but the satellites and base stations will have to receive and rebroadcast and the fiber optic network will likely at some point end up terminated at some router and then there will still be a number of hops to the destination.
- kbenson 9y agoThey aren't accounting for devices in the path for land nor space, so the question becomes are there more or less devices in the average path for each case, and by how much, and what's the average penalty occurred for each device in each case?
- jacquesm 9y agoUndersea optic cables use optical amplifiers, which is a pretty neat trick and does not introduce latency, and so should not count as a hop. https://en.wikipedia.org/wiki/Optical_amplifier https://en.wikipedia.org/wiki/Optical_amplifier In the end it is probably mostly a matter of how many hops that will determine which is the faster path, the two paths are mostly equal in other respects, I suspect the latency incurred for each hop is roughly the same, assuming they use error correction and re-transmission on the link layers between the satellites. If it all gets passed through blindly then it will be a bit quicker because there is no decoding step involved but I highly doubt that because it would lead to substantial inefficiencies and loss of capacity (the difference between a switched and hub). Smarter to be a bit slower and to maximize the routing capabilities of the satellites so as to optimize for the scarce resource: inter-satellite bandwidth.
- oh_sigh 9y agoYou're correct, but I don't know enough about satellites to know their retransmit delay, nor enough about fiber optics generally. I figured it all may offset because you'll never get a fiber optic cable to go exactly where you want it to go, and you may end up a mixed medium route with something like copper->fiber->copper->air->fiber->copper route, or something like that.
- 9y ago
- sgc 9y agoThe latency comment for repeaters someone else made is important, but it also won't be going in a circle between satellites, but in straight lines through the circle (as far as geometry allows), which will help shave a few ms.
- robocat 9y agoThe path between satellites would zig-zag. Presuming a flat surface of 200 X 200, and a random line across half of that, and presuming that satellites only communicate with nearest neighbours you can guesstimate that the extra distance is significant (ignoring other factors). If they can communicate with more distant satellites then distance could decrease (short cut segments around great circle).
- bpd1069 9y agoThe satellites will be meshed over 83 orbital planes starting around 1100km up. The satellites will connect to the farthest satellite it can see that makes the shortest path to the egress. So 2~3 hops verse a datacenter hops to the fiber ingress..then out the fiber across the atlantic.
- Robotbeat 9y agoThe path taken by fiber optic cables is at least as bad, though. Even before you count the slower speed of light in glass.
- azernik 9y agoI believe Iridium also uses its satellite-to-satellite crosslinks for backhaul. In fact, the SpaceX proposal looks a lot like the Iridium concept in general, but with thousands of little satellites instead of dozens of larger ones (which probably makes the implementation very different).
- kilroy123 9y agoWas going to mention the same. Half of their new constellations is up now. Apparently, you can use the commercially available hotspot devices that are out now. I'm curious how fast and well it will work.
- kevin_thibedeau 9y agoIt's Teledesic.
- azernik 9y agoHuh! Never heard of them before! (Which I guess is kind of the point.) Hopefully the telecoms market has changed enough since then (cf Iridium's recent profitability, even while launching a whole new constellation) to make it suddenly viable.
- 9y ago