Why Satellite Internet service is so slow

Why Satellite Internet service is so slow

Summary: I was reading in the news today about an experimental geosynchronous communications satellite being launched by Japan and I got to wondering about why Satellite Internet service has such horrendous latency and is so slow.  So I drew up a little diagram above (click to see full resolution) and did some calculations on the distance traveled and how long it takes for light to take the four-way journey.

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TOPICS: Networking, Browser
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Satellite in geosynchronous orbit

I was reading in the news today about an experimental geosynchronous communications satellite being launched by Japan and I got to wondering about why Satellite Internet service has such horrendous latency and is so slow.  So I drew up a little diagram above (click to see full resolution) and did some calculations on the distance traveled and how long it takes for light to take the four-way journey.  That's because you have to go up to the satellite, then back down to the service provider, then back up to the satellite, and finally back down to you.  Seeing that circle represent the planet Earth gives you some perspective how far and high a geosynchronous orbit is.

Here are some interesting numbers I compiled and estimated

  • 35,780 kilometer geosynchronous altitude
  • 12,756.32 kilometer diameter of earth at the equator
  • 12,715.43 kilometer diameter of earth at the poles
  • 299792.458 km/s is the speed of light in a vacuum
  • Just the speed of light delay is between 477 ms to 556 ms delay
  • With equipment delay and congestion, we're looking at 500 ms to 1000 ms delay for satellite Internet service.
  • ~199862 km/s is the speed of light in glass (assuming glass is 1.5x slower than in vacuum)
  • 39.6 ms theoretical ping from California to New York
  • 80 ms is the realistic ping from California to New York
  • 90.8 ms theoretical ping from California to Germany
  • 180 ms is the realistic ping from California to Germany
  • 100.8 ms theoretical ping from California to China
  • 200 ms is the realistic ping from California to China

Topics: Networking, Browser

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  • Real world is worse.

    Ping statistics for 75.104.128.61:
    Packets: Sent = 25, Received = 22, Lost = 3 (12% loss),
    Approximate round trip times in milli-seconds:
    Minimum = 626ms, Maximum = 3690ms, Average = 1385ms

    This is the nameserver within WildBlue's network -- this is a two-way system on an average day (even with spotbeams). I've never seen a ping within their network below 600ms, while 1300-1600 is typical, and those up in the 3000ms (and even 4000ms) range are not all that uncommon.

    While 1300ms isn't actually all that bad considering, the way HTTP works amplifies those delays. It can take anywhere from 5-8 seconds for a page to start rendering. It's not the speed either. 1Mbit/s isn't ideal, but it isn't going to cause those kinds of response delays.

    I've heard people say that early on in WildBlue's existence, everybody got latency in the 600-800ms range, but after a firmware update went out to all their satellite modems (DOCSIS (1.x?) compliant), everyone jumped into the 1300's, and have been there ever since. VoIP supposedly worked at one time -- while painfull -- but now I guess Skype won't even connect with that kind of latency, much less run.

    High latency, slow speeds compared to other options, expensive, doesn't just die when it rains, it actually dies just when heavy clouds roll in..but what can you do? Embarq is my telco and their/my exchange office only offers DSL to 18% of its customers, has been stuck at that number for 2 years, and seemingly has no interest in doing anything about it.

    Cable? Not here. Despite having 30 homes on this road and a high school, this is just one of the many areas of America being left behind.

    ..and satellite is not the solution.
    pwtenny
    • Yeah it's much worse in my experience too

      I completely agree with you. The half-second delay is strictly from the speed-of-light delay and that is WAY too high to be acceptable as is.

      "Cable? Not here. Despite having 30 homes on this road and a high school, this is just one of the many areas of America being left behind."

      Have you heard of the group Connect Kentucky?
      http://www.connectkentucky.org/

      I think they use Wi-Fi.
      georgeou
    • How far is the nearest town with an Internet link?

      How far is the nearest town with an Internet link? Maybe in one of those places with at least a DSL connection with line of sight to your little town, hook up a wi-fi parabolic dish and create a 20 mbps backhaul link. Then set up a large antenna for a huge hotspot to cover those 30 homes and the high school. I?ve actually been working on some of this stuff and if you email me, I?ll see what I can do to advise you.
      georgeou
      • Close, but mountainous area.

        There's 4mbit+ cable and supposedly 3mbit+ DSL within 10 minutes/5-6 miles, but topology is going to make that kind of wireless setup pretty difficult.

        I'll explain when I mail you -- thanks.
        pwtenny
        • Mountain are tough but can be solved

          Find a high point visible to that 3 Mbps DSL line and visible to those 30 homes and school. If that's not possible, you'll need two towers to relay the signal through some line-of-sight obstacles. Then you need a solar/wind powered tower with battery backup up there with a dish aimed at the location with the 3 Mbps DSL (forget Cable) and a dish aiming back at the tower. Then you would use a second sector antenna and aim it to cover those 30 homes. The question is whether you have the rights to install the tower at that site.

          The open source access point would need 2 radios but that's the cheap part. The expensive part is the tower and the power plant and batteries and installation. That will give you blanket Wi-Fi coverage over that area. To improve performance, be sure to prioritize VoIP and gaming traffic which are highly sensitive to latency. Also put an IPCop appliance at the house to cache content.

          I do wish they'd make a really small wind generator since the smallest ones are like 500 watts and you don't need that. Ideally it would be a very simple and small 100 watt wind generator.
          georgeou
    • Another satellite story with a happier ending

      I've been through the same situation. I was on WildBlue for 6 months and experienced performance degradation that went from bad (600-800ms latency) to worse (1200-1500ms). After many letters to the Denver BBB, I was able to break the contract. Their website claims 3secs to download a 150K website. I never saw this level of performance, and that was my primary argument. They finally admitted that the best I could expect was 15-20 seconds to download typical sites.

      We also have few options in our area, which is not served by DSL or cable. However, as George mentioned, there are wireless solutions. I discovered that I was line-of-site with a wireless ISP broadcasting from a 1500' TV tower (7 miles away). So I signed up with them after giving up on satellite.

      However, due to hills and trees, few of my neighbors could get a signal. It is also relatively expensive. I have now extended the wireless network to about 20 neighbors. Most of these people do not have line-of-site with me. The signal is daisy-chained from one house to the next. I've successfully connected to neighbors 5-6 hops away. The incoming bandwidth is 1-2mps with about 30-50ms latency. I am able to deliver ~500kbps to most neighbors with an added latency of another 5ms per hop. It's not perfect, but it works reasonably well, and much better than dial-up.

      From a technical standpoint I'm using Linksys (WRT54G) and Buffalo (WHR-G54S) ~50$ routers with DD-WRT firmware. The firmware allows the routers to work as repeaters, thus allowing the hops from house to house as well as local connections. I've been able to burn through some trees and extended the range using re-purposed satellite dishes to increase the gain.

      I also recently discovered that Sprint's network provides EVDO coverage in our area. The signal is on the weak side, but I can still get 500-700kbps uploads at ~125-175ms latency. With a wireless EVDO router this is now serving as a back-up link.

      Another option to explore is bringing in a T1 connection (1.44mbps) over standard phone wires. T1s are not limited by the DSL distance constraints. I could not do this since it requires many pairs, and running additional phone cable would be very expensive (underground in our area). But if you can get a T1 connection to one building (perhaps the school?) then you can extend that via a local wireless network. I've seen T1's advertised for $350-400$/month, which could be shared across 10-20 residents.
      WirelessWiz
  • RE: Why Satellite Internet service is so slow

    George,

    The polar radius of the earth is 6,356.750 km and the equatorial radius is 6,378.135 km. (See Wikipedia and other Internet sources).

    --rj

    http://oakleafblog.blogspot.com
    Roger_Jennings
    • Ah, my numbers and drawing were correct. I meant to label it diameter

      Ah, my numbers and drawing were correct. I meant to label it diameter. I did label one of them as diameter and the other as radius. Both should have been labeled as diameter.
      georgeou
  • High latency link impact on protocols

    To make matters worse, the TCP protocol itself introduces problems with satellite links. The three way handshake requires three round trips before data transfer begins. Windowing issues such as TCP slow-start also cause delays on high-latency links because packets must be acknowledged before the next is transmitted causing additional round trips. Higher layer protocols don't always help either. Consider HTTP 1.0 where a separate three-way handshake was established for each element on a web page (of course, this is better with 1.1).
    chrisaaa1
    • Agreed, it gets much worse

      nt
      georgeou
  • Please don't tell me some one asked you about this.

    But why can't we make the signal go faster than the speed of light?

    I honestly have a former classmate who plays WOW on satellite. That to me is a feat if anything. I had satellite through DirecWay back in the day. Though latency was crap, it was far better than the 24K connection I could get through the phone line. I was still a bit upset to find out about download limitations, but if satellites can proxy more data, I would be a bit happier. One time I did hit a file that was cached on the satellite and the data stream that I receive was a half a megabyte a second.

    I think a Wifi network would be better except in mountainous areas. Those were the first to get cable though.
    nucrash
    • It's been brought up before ;)

      I've had technical people ask that in meetings before - in front of other technical people. Typical case of not thinking the problem thru before asking the question...

      Seriously, though - we techies tend to inadvertently mislead the less technical around us. How often do we use the adjective "faster" (as in a faster pipe) when what we really mean is wider (as in wider bandwidth).

      We know the digital pulses travel down the kink as the same speed, regardless of whether it's a Bell 103-type 300 bit per second modem, or an OC-768 delivering a blistering 40Gb/s. What we really mean is delivering more bits per second per unit of time...

      Back to the first paragraph - I once had a mainframe operations manager (back in the '390 days) ask how we could make a link to a regional office faster to overcome latency effects. I had just explained seconds before how you couldn't. I used the example of a marble dropped down a 100-foot 1-inch diameter pipe - it doesn't fall any faster than a marble dropped down a 3-foot wide well. Even though you could drop thousands more marbles down the well, any application that expects you to acknowledge each marble separately AND still processes them sequentially will see no improvement. The manager still didn't get it.

      So I responded - give me the money to change the universal gravitational constant so I can increase the speed of light, and we'd get it done. Lot's of coffee got spilled on that one! :)
      NetArch.
      • tiny correction

        Again, we all know (or at least, should know) that effects of capacitance in a wired environment mean that electrical pulses do travel at a speed less than that of photons in an optical fiber, but you get my drift...
        NetArch.
      • Yeah, that sounds about right. Very few people understand the latency prob

        Yeah, that sounds about right. Very few people understand the latency problem and the effect it has on remote applications.

        However, it would be possible to reduce ping times with superior equipment. You can't make it faster than a straight arc over the surface of earth through a glass medium, but latency can be improved by minimizing congestion and equipment delay.
        georgeou
        • While this is true

          I would think that the market desires getting the majority of the market on a much cheaper budget and not bother spending millions on the last mile that would envelope most rural users.

          Satellite was probably the cheapest solution with Wireless being the next cheapest.

          Latency is still much better with land based wireless, although still crap.
          nucrash
      • Nothing an incoherent pump can't fix:-)

        Get a little superluminal velocities going with with a negative group velocity possible.

        Who knows, you might get a budget to do some cool experiments:-)

        Probably of minimal value and won't impact the latency issue but.... could be fun.
        Bruizer
      • Universal Gravitational Constant

        Did your manager put the expenditure in the capital or operating budget ?
        wes.sykes
  • RE: Why Satellite Internet service is so slow

    Thanks for the story. Include Blue sky and Hughes.

    I ping 488 with Vrizon. It's bad for games online, but ok otherwise.
    atari8bit