The radius of the earth is about 6400km. Geostationary orbit is, as you note, 36000km above the equator. The path from the satellite to the North Pole is the hypotenuse of a right triangle with legs of 6400km and (6400+36000)km. That gives a distance from the North Pole to the satellite of 43000km. It's reasonable to conclude that the distance from either New York or San Diego is less than that.
Is that 36000 km above the equator measures from the surface of the earth, or the center of the earth? I would assume that most companies would use the surface of the earth to determine the orbit, or sea level. Looking at a spam I just received from satcast.com, it looks like they are considering the distance from the dish to the satellite to be roughly 44000 miles. That's roughly 70000 km. Assuming that they are stating that from the dish to the bird, that would account for the larger RTT times that people see. My real problem with these directpc type systems are two fold. The first is that these systems use a USB connection. I use wireless at home since I have a number of laptops. I certainly am not willing to tie myself down to a usb cable. The second problem is that the users are addressed using rfc1918 address space and are translated via nat to the Internet. This may mess up any number of applications that I use, including VPN software. Add to this the first problem, and suddenly I have two levels of NAT that I have to contend with, one on my windows machine connected to the USB cable (with Internet sharing), and one at earthlink's edge. Those are what's keeping me at dialup, even though I only get 28.8 at best. Well... that and the fact that I can't get cable where I live, and the CO is sonething like 15 miles away (not that they can spell DSL out here). _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com
The radius of the earth is about 6400km. Geostationary orbit is, as you note, 36000km above the equator. The path from the satellite to the North Pole is the hypotenuse of a right triangle with legs of 6400km and (6400+36000)km. That gives a distance from the North Pole to the satellite of 43000km. It's reasonable to conclude that the distance from either New York or San Diego is less than that.
Is that 36000 km above the equator measures from the surface of the earth,
The surface of the Earth. (Or, more precisely, the surface of the Earth that is directly below the satellite. It's further to other parts of the surface of the earth. So, geostationary orbit is 36000km above the equator. Or (36000+6400)km from the center of the earth.)
Looking at a spam I just received from satcast.com, it looks like they are considering the distance from the dish to the satellite to be roughly 44000 miles. That's roughly 70000 km. Assuming that they are stating that from the dish to the bird, that would account for the larger RTT times that people see.
I'm not sure why spam should be considered a reliable source of information, but, anyway, there's nowhere on earth where the distance from the dish to a geosynch satellite is 44000 miles. I would guess that they are referring to the round-trip distance -- 22K miles up, 22K miles down. That's not surprising, since geostationary orbit is 22K miles above the equator. (They are presumably ignoring the slightly increased distance to the satellite from anywhere not directly under the satellite.) -- Brett
Ukyo Kuonji wrote (on Feb 27):
Looking at a spam I just received from satcast.com, it looks like they are considering the distance from the dish to the satellite to be roughly 44000 miles. That's roughly 70000 km. Assuming that they are stating that from the dish to the bird, that would account for the larger RTT times that people see.
We ran a similar service a number of years ago - which we managed to finally put to bed about a year ago. We had an issue that because most peoples use was HTTP, with short-lived connections, they never had a chance to open up their windows and make full use of the satellite link when empty and wouldn't shrink fast enough when busy. Dropped packets, retry galore, only making matters worse. I overcame this with a really nasty hack to a BSD kernel. Ran a HTTP proxy on it and made the TCP stack bias the start window size of a connection and how quickly it changed depending on the measured load of the uplink to the bird. People using this proxy had far fewer dropped packets and hung TCP sessions. It needed a ton of memory to do it and a lot of this had to be assigned to the kernel for network buffers, but it worked. We had window sizes in the region of 512k when the uplink was empty and atmospheric conditions didn't drop packets.
My real problem with these directpc type systems are two fold. The first is that these systems use a USB connection. I use wireless at home since I have a number of laptops. I certainly am not willing to tie myself down to a usb cable.
This was a DVB card in a PCI slot. Hauppage do similar these days I think.
The second problem is that the users are addressed using rfc1918 address space and are translated via nat to the Internet. This may mess up any number of applications that I use, including VPN software. Add to this the first problem, and suddenly I have two levels of NAT that I have to contend with, one on my windows machine connected to the USB cable (with Internet sharing), and one at earthlink's edge.
IMO, 1918 sucks at the best of times and you shouldn't be using it for customer addressing unless requested. Our system was cute in that you could control whether to use the satellite link for the toward-subscriber path or not, plus you could dial any number in our RAS pool, PSTN or ISDN, that you were authorised to use and it would work.
Those are what's keeping me at dialup, even though I only get 28.8 at best. Well... that and the fact that I can't get cable where I live, and the CO is sonething like 15 miles away (not that they can spell DSL out here).
I think I'd move. :) Regards, Chris. -- == chris@easynet.net T: +44 845 333 0122 == Global IP Network Engineering, Easynet Group PLC F: +44 845 333 0122
participants (3)
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Brett Frankenberger -
Chrisy Luke -
Ukyo Kuonji