by Tom Blakely
WARNING! Stunningly long piece to follow. Please use next restroom exit !... and bring me a cookie while you're up. Here we go:
So you're waaaaaaay out in the country, and neither DSL nor Cable is an option. Like say ..in Kosova. Or Bosnia. Or, God forbid, North Dakota. Perhaps on a ship. You'd like to get the internet, but carrier pigeon seems to be your only option. Wherever you are, if you're north of the equator and have a view of the visible sky to the south of you, you may have another option. You can probably get internet ...via Satellite. Yes, just like Wolf Bliitzer and James Bond you too can have nearly instant communications with the vast internet.
"Where do I sign up!" you cry out... Well... I wouldn't pop the champagne just yet. There's some issues we need to discuss, which I'm going to try to do in this editorial. Okay...You have to understand and remember one very simple premise:
Satellite communications are line of sight.
That one sentence is the core of what drives everything else. I won't go too much into the history as it's not relevant, except to mention Syncom2, the first Geostationary Satellite.
What the heck is a Geostationary Satellite anyways?
A Geostationary Satellite is a satellite or "bird" that is in a fixed position relative to the Earth. Kind of like your cars' drivers side mirror is in a fixed position relative to the rest of your car. If you turn left or right or even in a circle the mirror stays in it's fixed position relative to the rest of the vehicle. Make sense? A GeoSat follows the same premise, only on a larger scale and it uses physics to do so. First the how, then the why. I'm going to keep the math to a minimum.
Ever noticed that if you drop something it falls to the ground? So did the folks at NASA, and they got concerned because they didn't want satellites dropping out of the sky. It's embarrassing and expensive. So they had to try and find the point where the satellite would maintain enough speed to keep it from falling to earth while staying in a fixed spot over the equator.
Why do it this way?
Because satellites (like your car) only have so much gas or propulsion fuel. Unlike your car, when they run out, that's it. They can no longer maneuver. If they're too close they fall into the atmosphere slowly but inevitably. If they're too far out they simply slowly drift away into space. So the idea was to put them at a place where the speed of the satellite is sufficient to keep it from falling to earth yet have a rotation of one day. This keeps the satellite in it's position. A combination of forces trying to equal out to a stable area.
22,300 miles over the equator there is a whole belt of satellites zooming along. This area is named after Sir Dr. Arthur C. Clarke the science-fiction novelist. It is frequently referred to as "Clarke's Constellation" Because it was he, back in 1947, who postulated the idea of using satellites for point-to-point-to-point radio communication. Science Fiction indeed.
Why a fixed position? Why Line of sight?
Satellites are expensive. If you can have one cover a large area it's more cost effective than having two or three. In addition, we don't want to keep trying to find satellites every day. So we keep them at fixed positions so once we're locked in and pointed at the satellite we don't have to worry about tracking it across the sky. It's that simple. There are other reasons as well, but those are the most important ones.
Now.. Line of Sight...
Okay...
If you think about it, you'll realize that from where you are standing right now, you can see some things that are farther away from you than other things. This is frequently because they are taller. They have more "Altitude". For instance you can see the top of a water tower long before you can see the pumping station underneath it. So we know that the greater the height, the farther away you can "see" something.
Geostationary Satellites are at fixed positions at an altitude of 22,300 miles from Earth. They can "see" (and be seen from) a huge area of land and ocean, and this area they can "see" is called the "footprint". They are also frequently located over the equator. You can imagine what the foot print looks like by holding a flashlight at a fixed distance from a basketball and turning the light on. The closer you get, the smaller the footprint. Make sense?
Now if you hold the flash light at a fixed distance from the centerline or "equator" of the basketball AND aim it at the upper half you will see that the "footprint" elongates and gets much larger on one side, extending itself by half again. And turning from a simple circle, into an oval. That's why a lot of birds are "parked" in orbit over the equator. There is a consequence to this large footprint though. Radio waves travel at the speed of light, or about 186,000 miles per second. So any traffic from you to the satellite has to go 22,300 miles up, go through the satellite, and be retransmitted 22,300 miles back down.
The net effect is that it adds about a minimum of 240ms to the round trip. This is from an ideal position as close to the satellite as possible, which is probably in the ocean at the equator. And remember, that if you send for a web page both the request and the response have to travel these distances in addition to any ground distance. A more realistic expectation is a response of about 500-1000ms.
What is this "200ms" stuff?
Briefly: 1000ms (milliseconds) equals one second. The satellite internet systems currently available run about a half second delay because of the distances involved. To an average web surfer this means about one half a second MINIMUM, between the time you click a link and the time you start to see a change take place. On a practical level it's probably closer to 3/4 of a second response time (750ms). Unfortunately, if you're heavy into internet multiplayer gaming, then we're pretty much done here. You can go elsewhere because a 750ms plus response time is unplayable. Why?
Imagine you are driving a racecar. Now imagine it's about three-quarters of a second delay (750ms) between the time you try to steer left, and the time the racecar starts to respond (750ms). You see the problem. It's like driving on ice and is simply not useable for many internet games that require fast reflexes. Some flight games may be useable, because they don't need as fast a response. However, popular first person shooters like Quake III and Tribes 2 and Counter-Strike are almost unplayable.
If, on the other hand, you're not as big into gaming and are in an area not serviced by DSL or cable then Internet via Satellite may be just the thing for you.
I'm sure you're tired of the history lesson and would like me to get on with how you can get it if you want it.
You have two primary options right now.
Hughes is beginning to offer satellite service in conjunction with it's DirecTV product, not surprisingly called DirecPC. You can buy it separately or bundled, thus giving them twice the access to your wallet. OTOH, since you already are getting a a satellite dish for the internet why not also use it for TV. In any case, the Hughes system used to be referred to as a Hybrid or "dial-in return" system. Hughes is now switching over to a true two-way satellite system. The difference between the two types is that in the older system you HAD to have a landline and a modem to dial in. Your request for a web page would go via landline/modem to Hughes, who would retrieve the page, and then downlink it to you via the satellite.
THE NEW SYSTEMS CONDUCT YOUR REQUESTS AND THE RESPONSES FROM HUGHES ENTIRELY VIA SATELLITE. THERE IS NO LANDLINE/MODEM.
The new terminal you receive when you purchase the product has both a receiver, and a transmitter. A terminal is simply a box that houses some equipment. In this case.. a receiver and a transmitter. Hook it up to the dish, point it at the satellite and start surfing. More or less. There's always details but that's the crux of it.
The Other system is by Gilat, and is being sponsored by Microsoft and Radio Shack. It also uses the newer two way satellite system. It is part of the DiSH Network for TV access and is called StarBand.
The nice thing about these systems is that service is available just about everywhere in North America and Europe, and many places in South America as well.
I would like to mention this:
While each company claims multi-megabit performance it's more reasonable to expect about a 768kbit downlink / 128kbit uplink speed. This is based more on TCP issues and the corporate advertising tends to run smack into some real world physics issues. This is long enough and I won't bore you with too much detail but there are some inherent limitations due to TCP receive window size and receive acknowledgement timing.
I hope this primer leaves you with a clearer understanding of the theory and operational issues with Satellite Internet access. As an aside there are some Low Earth Orbit/Observable satellites called "LEO's" which promise to offer all the current systems do, and more. Including MUCH lower delay times in the 10 to 20ms range. These systems, however, aren't slated to come online until about 2005 if they ever do. So for the time being, you'll just have to accept the delay inherent in the system.
In alphabetical order:
Hudhes : www.directpc.com
Gilat / Microsoft : www.starband.com
Average pricing is between $40 - $60 USD a month. Some require you to buy more equipment than others and both run specials and deals so prices will tend to vary.
Finally, I want to mention this. Satellite internet represents the best opportunity for schools, communities, and individuals in remote areas to gain access to world wide communications. It is unique because it is simply not subject to local control over access or content. It has the ability to reach people no other communications medium can at a practical cost.
Regards,
Thomas Blakely, CCNA, CCDA
- Bouncer -
So you're waaaaaaay out in the country, and neither DSL nor Cable is an option. Like say ..in Kosova. Or Bosnia. Or, God forbid, North Dakota. Perhaps on a ship. You'd like to get the internet, but carrier pigeon seems to be your only option. Wherever you are, if you're north of the equator and have a view of the visible sky to the south of you, you may have another option. You can probably get internet ...via Satellite. Yes, just like Wolf Bliitzer and James Bond you too can have nearly instant communications with the vast internet.
"Where do I sign up!" you cry out... Well... I wouldn't pop the champagne just yet. There's some issues we need to discuss, which I'm going to try to do in this editorial. Okay...You have to understand and remember one very simple premise:
Satellite communications are line of sight.
That one sentence is the core of what drives everything else. I won't go too much into the history as it's not relevant, except to mention Syncom2, the first Geostationary Satellite.
What the heck is a Geostationary Satellite anyways?
A Geostationary Satellite is a satellite or "bird" that is in a fixed position relative to the Earth. Kind of like your cars' drivers side mirror is in a fixed position relative to the rest of your car. If you turn left or right or even in a circle the mirror stays in it's fixed position relative to the rest of the vehicle. Make sense? A GeoSat follows the same premise, only on a larger scale and it uses physics to do so. First the how, then the why. I'm going to keep the math to a minimum.
Ever noticed that if you drop something it falls to the ground? So did the folks at NASA, and they got concerned because they didn't want satellites dropping out of the sky. It's embarrassing and expensive. So they had to try and find the point where the satellite would maintain enough speed to keep it from falling to earth while staying in a fixed spot over the equator.
Why do it this way?
Because satellites (like your car) only have so much gas or propulsion fuel. Unlike your car, when they run out, that's it. They can no longer maneuver. If they're too close they fall into the atmosphere slowly but inevitably. If they're too far out they simply slowly drift away into space. So the idea was to put them at a place where the speed of the satellite is sufficient to keep it from falling to earth yet have a rotation of one day. This keeps the satellite in it's position. A combination of forces trying to equal out to a stable area.
22,300 miles over the equator there is a whole belt of satellites zooming along. This area is named after Sir Dr. Arthur C. Clarke the science-fiction novelist. It is frequently referred to as "Clarke's Constellation" Because it was he, back in 1947, who postulated the idea of using satellites for point-to-point-to-point radio communication. Science Fiction indeed.
Why a fixed position? Why Line of sight?
Satellites are expensive. If you can have one cover a large area it's more cost effective than having two or three. In addition, we don't want to keep trying to find satellites every day. So we keep them at fixed positions so once we're locked in and pointed at the satellite we don't have to worry about tracking it across the sky. It's that simple. There are other reasons as well, but those are the most important ones.
Now.. Line of Sight...
Okay...
If you think about it, you'll realize that from where you are standing right now, you can see some things that are farther away from you than other things. This is frequently because they are taller. They have more "Altitude". For instance you can see the top of a water tower long before you can see the pumping station underneath it. So we know that the greater the height, the farther away you can "see" something.
Geostationary Satellites are at fixed positions at an altitude of 22,300 miles from Earth. They can "see" (and be seen from) a huge area of land and ocean, and this area they can "see" is called the "footprint". They are also frequently located over the equator. You can imagine what the foot print looks like by holding a flashlight at a fixed distance from a basketball and turning the light on. The closer you get, the smaller the footprint. Make sense?
Now if you hold the flash light at a fixed distance from the centerline or "equator" of the basketball AND aim it at the upper half you will see that the "footprint" elongates and gets much larger on one side, extending itself by half again. And turning from a simple circle, into an oval. That's why a lot of birds are "parked" in orbit over the equator. There is a consequence to this large footprint though. Radio waves travel at the speed of light, or about 186,000 miles per second. So any traffic from you to the satellite has to go 22,300 miles up, go through the satellite, and be retransmitted 22,300 miles back down.
The net effect is that it adds about a minimum of 240ms to the round trip. This is from an ideal position as close to the satellite as possible, which is probably in the ocean at the equator. And remember, that if you send for a web page both the request and the response have to travel these distances in addition to any ground distance. A more realistic expectation is a response of about 500-1000ms.
What is this "200ms" stuff?
Briefly: 1000ms (milliseconds) equals one second. The satellite internet systems currently available run about a half second delay because of the distances involved. To an average web surfer this means about one half a second MINIMUM, between the time you click a link and the time you start to see a change take place. On a practical level it's probably closer to 3/4 of a second response time (750ms). Unfortunately, if you're heavy into internet multiplayer gaming, then we're pretty much done here. You can go elsewhere because a 750ms plus response time is unplayable. Why?
Imagine you are driving a racecar. Now imagine it's about three-quarters of a second delay (750ms) between the time you try to steer left, and the time the racecar starts to respond (750ms). You see the problem. It's like driving on ice and is simply not useable for many internet games that require fast reflexes. Some flight games may be useable, because they don't need as fast a response. However, popular first person shooters like Quake III and Tribes 2 and Counter-Strike are almost unplayable.
If, on the other hand, you're not as big into gaming and are in an area not serviced by DSL or cable then Internet via Satellite may be just the thing for you.
I'm sure you're tired of the history lesson and would like me to get on with how you can get it if you want it.
You have two primary options right now.
Hughes is beginning to offer satellite service in conjunction with it's DirecTV product, not surprisingly called DirecPC. You can buy it separately or bundled, thus giving them twice the access to your wallet. OTOH, since you already are getting a a satellite dish for the internet why not also use it for TV. In any case, the Hughes system used to be referred to as a Hybrid or "dial-in return" system. Hughes is now switching over to a true two-way satellite system. The difference between the two types is that in the older system you HAD to have a landline and a modem to dial in. Your request for a web page would go via landline/modem to Hughes, who would retrieve the page, and then downlink it to you via the satellite.
THE NEW SYSTEMS CONDUCT YOUR REQUESTS AND THE RESPONSES FROM HUGHES ENTIRELY VIA SATELLITE. THERE IS NO LANDLINE/MODEM.
The new terminal you receive when you purchase the product has both a receiver, and a transmitter. A terminal is simply a box that houses some equipment. In this case.. a receiver and a transmitter. Hook it up to the dish, point it at the satellite and start surfing. More or less. There's always details but that's the crux of it.
The Other system is by Gilat, and is being sponsored by Microsoft and Radio Shack. It also uses the newer two way satellite system. It is part of the DiSH Network for TV access and is called StarBand.
The nice thing about these systems is that service is available just about everywhere in North America and Europe, and many places in South America as well.
I would like to mention this:
While each company claims multi-megabit performance it's more reasonable to expect about a 768kbit downlink / 128kbit uplink speed. This is based more on TCP issues and the corporate advertising tends to run smack into some real world physics issues. This is long enough and I won't bore you with too much detail but there are some inherent limitations due to TCP receive window size and receive acknowledgement timing.
I hope this primer leaves you with a clearer understanding of the theory and operational issues with Satellite Internet access. As an aside there are some Low Earth Orbit/Observable satellites called "LEO's" which promise to offer all the current systems do, and more. Including MUCH lower delay times in the 10 to 20ms range. These systems, however, aren't slated to come online until about 2005 if they ever do. So for the time being, you'll just have to accept the delay inherent in the system.
In alphabetical order:
Hudhes : www.directpc.com
Gilat / Microsoft : www.starband.com
Average pricing is between $40 - $60 USD a month. Some require you to buy more equipment than others and both run specials and deals so prices will tend to vary.
Finally, I want to mention this. Satellite internet represents the best opportunity for schools, communities, and individuals in remote areas to gain access to world wide communications. It is unique because it is simply not subject to local control over access or content. It has the ability to reach people no other communications medium can at a practical cost.
Regards,
Thomas Blakely, CCNA, CCDA
- Bouncer -
No comments:
Post a Comment