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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: Satellite latency
Not to mention that -5 degree or so look angle (negative elevation) from the poles being hard to acquire. ;) But with enough elevation and a big enough dish... Also about that satellite drift...The earth wobbles during rotation meaning geo stats do small figure 8s overhead. IIRC there is some computer software out there (from my days of TVRO in Europe) that given a latitude/longitude and sat placement would return a time where the sat was in the middle of that 8 so you could best aim the dish. Or maybe I just had too much Heineken at the bar, can't remember which. Just my 2�. The delete key is your friend. -Al -----Original Message----- From: Michael Painter [mailto:[email protected]] Sent: Wednesday, February 27, 2002 12:22 PM To: [email protected] Subject: Re: Satellite latency ----- Original Message ----- From: "Leo Bicknell" <[email protected]> To: "Steven M. Bellovin" <[email protected]> Cc: "Tim Devries" <[email protected]>; <[email protected]> Sent: Tuesday, February 26, 2002 5:27 PM Subject: Re: Satellite latency >>Remember that a geosynchronous satellte must orbit the equator. Let's say for the sake of argument it's over mexico, you're in New York, and the downlink station is in San Diego. The 36,000 is the distance straight "down" to mexico, It's probably more like 50,000 to New York, and 45,000 to San Diego. And if you're in New York, and your mail server is in New York, but the downlink was to San Diego, you've got another 4,000 across country. Now you're up closer to 100,000km.<< Not wanting to get picky about ~20,000 km., but the maximum -usable- slant path is ~41,000 km. --Michael > > In a message written on Tue, Feb 26, 2002 at 09:07:14PM -0500, Steven M. Bellovin wrote: > > Geosynchronous orbit is about 36,000 km from the center of the earth. > > Round-trip to the satellite is ~72,000 km; the speed of light is > > 300,000 km/sec. That works out to 240 milliseconds at the minimum for > > one-way packet delivery. > > Remember that a geosynchronous satellte must orbit the equator. > Let's say for the sake of argument it's over mexico, you're in New > York, and the downlink station is in San Diego. The 36,000 is the > distance straight "down" to mexico, It's probably more like 50,000 > to New York, and 45,000 to San Diego. And if you're in New York, > and your mail server is in New York, but the downlink was to San > Diego, you've got another 4,000 across country. Now you're up > closer to 100,000km. > > Add to this some inefficient encoding done on satellites, and most > (consumer) systems using a broadcast medium that can buffer packets > and you see why people report 1 second RTT's with services like > StarBand. > > It's better than nothing, but it's a rough primary connection. > > -- > Leo Bicknell - [email protected] - CCIE 3440 > PGP keys at http://www.ufp.org/~bicknell/ > Read TMBG List - [email protected], www.tmbg.org >
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