Why is satellite Internet service so slow?

[Technoguy3]

I don't have it personally (because cable is better), but I've always thought that satellite internet would be the perfect way to get Internet access available worldwide. But frankly, it's slow! The absolute fastest you can ever get is 5Mbps.

As I have heard it, there is much more bandwidth made available to satellites, so why is satellite Internet service so slow? Doesn't my satellite HD television service use up more bandwidth?

I am by no means an expert; that's why I am asking to see if anyone here is. Thanks!

[Monkeh]

Extremely high latency.

[RJSC]

Extremely high latency.

Elaborating a bit, using Geo Stationary Satellites (which appear to be at a fixed point in the sky so that you can aim an antenna to them) the signal has to travel around  36000 km up to the satellite and then another 36000km down to the ISP, and that takes some time even at the speed of light.
It takes a signal 240 milliseconds to go up and down again.

More on: http://en.wikipedia.org/wiki/Geosynchronous_satellite

[johnnyfp]

Satellite download speed can be and is very fast, I'E you can download something really really quickly.

The slow bit is the latency, the time it takes to respond to a request. So for example, if you issue a command to download a file, that command takes 10 seconds to reach the server, the server then sends the file that you want but does not arrive for 10seconds. But when it does arrive it arrives fast.

So Satellite is great for downloading and uploading things, but not so great at instant responses from requests, So will sux at Online First person gaming or Skype call conversations.

[Monkeh]

So Satellite is great for downloading and uploading things

Not with TCP it's not.

[johnnyfp]

True, but who downloads with TCP these days 

[Monkeh]

True, but who downloads with TCP these days 

Oh, HTTP, FTP, SFTP..

[johnnyfp]

Well apart from HTTP,FTP,SFTP,SMTP,TELNET,IMAP,POP, who downloads with TCP!!!

[mariush]

The sats also have limited bandwidth, a few hundred megabits... this is sent towards the Earth and each user's antenna in theory receives all that.

Like it was already said, there's a question of distance between the satellite and the ground. The trip takes 100-120 ms one way (maybe a different number, but I'm too lazy to do the math now).

If your plan is two way, then basically means any request you make goes up to the satellite, then back down, then to the ISP and then the ISP has to send it back up and it has to come down.
If your plan is one way (as in download only from sat, upload on ground connection) you just save a trip through the satellite.

Also keep in mind not all ISP companies have the uplink in their own yard - a lot of them just process your computer's requests and group the data your computer needs with other data from other users and its streamed through fiber optics to a center that has the large antennas which can upload reliably to the satellite.
These can very well be in another country, if we're talking about Europe - so between your ISP and the upload to the satellite can be an additional 20-50 ms of latency, simply from routing the data to be uploaded to the "upload center"

So latency is a big issue.

The next is the bandwidth. Like I said, the whole satellite has a few hundred megabits. I know some specialized sats are supposed to come online with a few gigabits so lets assume the whole satellite does 1 gbps.

A satellite costs in the tens of millions of dollars and has a lifetime of about 20-30 years, maybe even less. So the costs have to be recovered during its lifetime. Therefore the actual upload to a satellite and reserved bandwidth costs a ton. I don't know exact numbers but a year or so ago, I heard it costs more than $10k a month to reserve a slot for one or two standard definition channels (so about 10-20 mbps)

People offering internet through satellite make profit only by sharing that downstream bandwidth, that's why you get an average of 5 mbps or something like that. Thousands of users are sharing a small bandwidth pool.

With cable, there's no problem with saturating the bandwidth, as close to you the cable goes in a box and from that point, the bits go through fiber cable through the ISP.

[Psi]

There was a bit about sat internet on the TV in NZ a few days ago and i remember the details

It was $99 a month for a connection with 2GB of data.  They didn't mention the speed other than to say it was fast broadband.

[nitro2k01]

Well apart from HTTP,FTP,SFTP,SMTP,TELNET,IMAP,POP, who downloads with TCP!!!

Even your beloved torrentz will mostly use TCP.

[Hypernova]

TCP can still be tuned to DL fast on a sat in some cases, IIRC there is a way to set the maximum number of packets the server will send before stopping due to no confirmation packets. So if you set the number high enough the latency can be factored into the transmission.

[NiHaoMike]

It takes a signal 240 milliseconds to go up and down again.

Double that to 480ms for round trip. Add in other causes of latency and it's easily over half a second.

The interesting part is that it really doesn't take very much bandwidth to give an impression of "fast" web browsing. But bandwidth sells so ISPs have been upping bandwidth for a long time already. And then they throw in caps "to reduce slowdowns". First off, the cost to keep a link up depends almost nothing on how much the link is used. Also, downloading 1GB on peak is very different from downloading 1GB off peak as far as the network is concerned.

In any case, I advocate extremely aggressive compression and caching since computing power and storage improve at much faster rates than communications. As Tiffany Yep might say, "The bandwidth of the air is almost infinite, but our ability to make use of it isn't."

[westfw]

TCP (on which almost all current internet protocols are run) maxes out at one window of data per round trip time, not counting limits that may imposed to save memory in the servers.  MOST clients are not going to be tuned for very high-delay links.  There are some auto-tuning features, but they react relatively slowly on a per-connection basis in order to avoid congesting the network, and thus won't show up unless an individual transfer is significantly large compared to the delay*bandwidth product.  A typical web page has lots of relatively short files, and is a horrible way to transmit a lot of data :-(

And 5Mbps isn't "slow."
"And you kids who complain that the World Wide Web
Is too slow oughtta cut out your bitchin’,
 ’Cuz when I was a boy every packet
Was delivered by carrier pigeon..."

[nitro2k01]

And 5Mbps isn't "slow."
"And you kids who complain that the World Wide Web
Is too slow oughtta cut out your bitchin’,
’Cuz when I was a boy every packet
Was delivered by carrier pigeon..."

Useless trivia: RFC1149 has actually been tried once as an experiment and had something like a 50% packet loss. Not to bad for an animal phy, I guess.

[notsob]

I once was called to advise on a problem a company agency was having with their system  ( this is back in the old fixed line days ( ie no adsl, & ISDN - I Smell Dollars Now was just beginning).
Basically - when they typed a character on the keyboard, it took seconds to appear on the screen. I connected a data analyser and observed the event.

So what was happening.

They were accessing a unix host which used character echo, so the host needed to see the keyboard character, & then 'echo' it to the screen (display), and they were using a satellite link to the host in another city.

So as mentioned above - as a broadcast system - ie someone sends continuous info to you, sat is wonderful.

Where interaction is required, sat is woesome, and remember, many many comms protocols have "hidden from the user", internal ack (handshake) protocols.

[SeanB]

Yes, but was faster than Telkom "Fastest" ADSL over a 50km trip, for a 1gig file..........

[jerry507]

So many posts about latency. The original poster clearly isn't talking about it's apparent speed, but it's throughput. Latency isn't a concern if you're talking about maximum throughput.

A satellite has a loooooooot of bandwidth, but it's exactly one asset mixed with a tremendous amount of users. While a wired network can simply mass high bandwidth lines to aggregate more and more users, it doesn't work like that for a satellite. You can't at this point realistically aggregate multiple satellites handling multiple users and then feed it all back. You send to A satellite which then sends back to A groundstation. Point to Point.

Also, the demand just isn't there. Most users in the US now are construction and oil/gas setups, and they want to check email and be reasonably cheap.

[Monkeh]

So many posts about latency. The original poster clearly isn't talking about it's apparent speed, but it's throughput. Latency isn't a concern if you're talking about maximum throughput.

Yes, it is, if you're dealing with TCP. Which you are.

[jerry507]

When you say TCP you're talking about an application specific throughput. A 5Mbps connection as advertised, or even a T1 or whatever else, isn't rated for speed using TCP. If you want to talk about TCP, you're talking about how fast it "feels" as you wait for handshakes.

[Monkeh]

When you say TCP you're talking about an application specific throughput. A 5Mbps connection as advertised, or even a T1 or whatever else, isn't rated for speed using TCP. If you want to talk about TCP, you're talking about how fast it "feels" as you wait for handshakes.

.. No, I'm talking about the actual, achievable throughput when using TCP. Which most everything does.

[jerry507]

Right, and I understand what you're saying. The OP is talking about why he can only get a 5Mbps pipe though. It has absolutely nothing to do with latency and everything to do with the smaller throughput of the asset being used compared to a wired network. Even sending data straight through with no need for any response.

[Monkeh]

Right, and I understand what you're saying. The OP is talking about why he can only get a 5Mbps pipe though. It has absolutely nothing to do with latency and everything to do with the smaller throughput of the asset being used compared to a wired network. Even sending data straight through with no need for any response.

Point, however the TCP issues are probably part of the reason they don't offer a larger pipe.

[jerry507]

Absolutely. Apparently there are LEO networks that can offer services of about 1Gbps. The RT times are i the range of 40ms compared to the GEO satellites. But I believe those require tracking dishes of at least one axis.