4 ms·

Geosynchronous satellite latency in best case: 250ms LEO latency best case: 6ms I've used those Hughes satellite connections before, I never got anything clos

Geosynchronous satellite latency in best case: 250ms LEO latency best case: 6ms I've used those Hughes satellite connections before, I never got anything close to 250ms. More like 400ms.

Diederich 8y ago
> LEO latency best case: 6ms Light travels about 1800km in 6ms, but that's just one way. Straight up and straight down at 550km is 3.6ms.
- gameswithgo 8y ago
  light is slower in the atmosphere, did you adjust for that?
  - Rebelgecko 8y ago
    Speed of light in air is still ~0.9997c (and approaches 1 as altitude increases), so it's a much less noticeable difference than it is for copper or glass
walrus01 8y ago
The absolute minimum latency you'll ever see with geostationary is about 489ms. That's assuming 1:1 dedicated transponder capacity and something like a higher end SCPC terminal and modem, accounting for latency and modulation/coding/FEC by the satellite modems on both ends. Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.
- shaklee3 8y ago
  This should probably tell you something about spacex's claims as well. The actual latency is never just the slant range. There's a ton of processing and network switching too.
  - walrus01 8y ago
    I am pretty optimistic about SpaceX's claims for what the space-segment latency will be. If you look at the system architecture for current generation high-bandwidth Ka-band geostationary services, which has dozens of spot beams on North America, there's about 30 teleports spread out around the US and Canada. These allow Viasat and Hughesnet customers, and similar, to consume capacity in the same spot beam as the teleport they're uplinked from (vs the satellite cross-linking a set of kHz from one Ka-band spot beam to another). For example, customers in really rural areas of Wyoming are going to connect to a teleport that's in Cheyenne, which will usually be in the same spot beam. Sites in Cheyenne near the railway have really good terrestrial fiber capacity for an earth station operator to buy N x 10 or 100GbE L2 transport links to the nearest major city. It would be technically possible, but uneconomical and an inefficient use of space segment transponder kHz to have customers in Wyoming moving traffic through a teleport in the Chicago area. Here's an illustration of Ka-band spot beams on a typical state of the art geostationary satellite: http://www.southwestsatelliteinternet.com/images/Ka-band-spot-beams.gif http://www.southwestsatelliteinternet.com/images/Ka-band-spo... Applying the same concept to starlink, telesat's proposed system, and oneweb, if they build a number of teleports geographically distributed near rural areas, it will allow individual satellites to serve as bent-pipe architecture from CPE --> Teleport, within the same moving LEO spot beams, or to have customer traffic take only one hop through space to an adjacent satellite before it hits the trunk link to an earth station. For example customers in a really rural area of north Idaho along US95 might "see" a set of moving satellites that also have visibility to an earth station in Lewiston, ID, where carrier grade terrestrial fiber links are available. Or a customer in a remote mountainous area of eastern Oregon may uplink/downlink through a teleport in Bend. The ultimate capacity of the system will be determined by how few hops through space they can get the traffic to do. Since every satellite will be identical and capable of forming a trunk link to a starlink-operated earth station, when it's overhead of it, they have an incentive to build a large number of earth stations geographically distributed around the world. It's basically the same idea as o3b's architecture but at a much smaller scale.
    - shaklee3 8y ago
      I don't doubt the latency in space numbers. What I don't believe is using a theoretical distance to compute latency. As you said, a LOT of that latency can come from scheduling inefficiencies and congestion. Each of their satellites has a relatively small amount of bandwidth, so if you happen to be in a beam with a lot of people, you'll be hit hard by this. As far as I know, their satellites are not capable of steering beams, and rely purely on the placement directly down from where they are. Another consideration: adding another 50ms to GEO latency isn't really going to change anyone's opinion. It's still targeted towards streaming, and latency doesn't matter as much since they're not targeting real-time gamers. SpaceX needs the latency to be very low to hit that market. There's a world of difference going from a 30ms ping to an 80ms ping, and once you're past a certain point, it puts you in the same camp as GEO.

Geosynchronous satellite latency in best case: 250ms LEO latency best case: 6ms I've used those Hughes satellite connections before, I never got anything close to 250ms. More like 400ms.

Diederich 8y ago

> LEO latency best case: 6ms Light travels about 1800km in 6ms, but that's just one way. Straight up and straight down at 550km is 3.6ms.

gameswithgo 8y ago
light is slower in the atmosphere, did you adjust for that?
- Rebelgecko 8y ago
  Speed of light in air is still ~0.9997c (and approaches 1 as altitude increases), so it's a much less noticeable difference than it is for copper or glass

walrus01 8y ago

The absolute minimum latency you'll ever see with geostationary is about 489ms. That's assuming 1:1 dedicated transponder capacity and something like a higher end SCPC terminal and modem, accounting for latency and modulation/coding/FEC by the satellite modems on both ends. Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.

shaklee3 8y ago
This should probably tell you something about spacex's claims as well. The actual latency is never just the slant range. There's a ton of processing and network switching too.
- walrus01 8y ago
  I am pretty optimistic about SpaceX's claims for what the space-segment latency will be. If you look at the system architecture for current generation high-bandwidth Ka-band geostationary services, which has dozens of spot beams on North America, there's about 30 teleports spread out around the US and Canada. These allow Viasat and Hughesnet customers, and similar, to consume capacity in the same spot beam as the teleport they're uplinked from (vs the satellite cross-linking a set of kHz from one Ka-band spot beam to another). For example, customers in really rural areas of Wyoming are going to connect to a teleport that's in Cheyenne, which will usually be in the same spot beam. Sites in Cheyenne near the railway have really good terrestrial fiber capacity for an earth station operator to buy N x 10 or 100GbE L2 transport links to the nearest major city. It would be technically possible, but uneconomical and an inefficient use of space segment transponder kHz to have customers in Wyoming moving traffic through a teleport in the Chicago area. Here's an illustration of Ka-band spot beams on a typical state of the art geostationary satellite: http://www.southwestsatelliteinternet.com/images/Ka-band-spot-beams.gif http://www.southwestsatelliteinternet.com/images/Ka-band-spo... Applying the same concept to starlink, telesat's proposed system, and oneweb, if they build a number of teleports geographically distributed near rural areas, it will allow individual satellites to serve as bent-pipe architecture from CPE --> Teleport, within the same moving LEO spot beams, or to have customer traffic take only one hop through space to an adjacent satellite before it hits the trunk link to an earth station. For example customers in a really rural area of north Idaho along US95 might "see" a set of moving satellites that also have visibility to an earth station in Lewiston, ID, where carrier grade terrestrial fiber links are available. Or a customer in a remote mountainous area of eastern Oregon may uplink/downlink through a teleport in Bend. The ultimate capacity of the system will be determined by how few hops through space they can get the traffic to do. Since every satellite will be identical and capable of forming a trunk link to a starlink-operated earth station, when it's overhead of it, they have an incentive to build a large number of earth stations geographically distributed around the world. It's basically the same idea as o3b's architecture but at a much smaller scale.
  - shaklee3 8y ago
    I don't doubt the latency in space numbers. What I don't believe is using a theoretical distance to compute latency. As you said, a LOT of that latency can come from scheduling inefficiencies and congestion. Each of their satellites has a relatively small amount of bandwidth, so if you happen to be in a beam with a lot of people, you'll be hit hard by this. As far as I know, their satellites are not capable of steering beams, and rely purely on the placement directly down from where they are. Another consideration: adding another 50ms to GEO latency isn't really going to change anyone's opinion. It's still targeted towards streaming, and latency doesn't matter as much since they're not targeting real-time gamers. SpaceX needs the latency to be very low to hit that market. There's a world of difference going from a 30ms ping to an 80ms ping, and once you're past a certain point, it puts you in the same camp as GEO.