[AusNOG] NBN Satellite Latency

[Ross Wheeler]

On Sun, 5 Feb 2017, Andrew McN wrote:

>> If the sat is at say, 45 degrees elevation (and at the same latitude,
>> which it probably isn't), then that path just became 31,438 miles =
>> 169ms each way. The closer to the horizon, the longer the path and the
>> higher the travel time...  and the further from the equator you are, the
>> greater the distance too.
>
> This is a substantial over-estimation of the difference in distance when
> away from the equator.  Flat earth thinking even, which would be close
> enough if the geostationary orbit height were small relative to the
> radius of the earth, but it's not.
>
> By my calculation, the distance to the satellite at the 45th parallel
> should only be about 6% worse than at the equator.  Even at the pole
> it's only 19% worse.

You've mixed up two of my points. I was not suggesting the offset was only 
latitude. I was saying if the bird was at 45 degrees elevation (ie, from 
the horizon) not at 45 degrees latitude!

My comment about latitude was only that "being further from the equator 
only adds to the delay".


> If people are finding that where the satellite is in the sky matters
> much to their ping time, then it seems that they should look to
> explanations other than the travel time at the speed of light.

It doesn't matter where the geostationary satellite is, satellite delay is 
and will always be "undesirable" (if not unusable) for the sort of 
real-time interactive stuff I do, including almost exclusively CLI 
environment, VoIP, telepresence (controlling things remotely)... and lets 
not even consider gaming.

R.