I have called the US from both Korea and Iraq and the conversations have been in real time. I would assume that the speed of the traffic over the phone lines is limited to the speed of light. So there should be a delay of several seconds to call the East Coast of the US from Korea, but there is not. Can someone explain what common sense thing I am overlooking?
SSG Schwartz
Because light travels very fast, and that’s not that far a distance. You perceive it as instant.
The speed of light is a LOT faster than that. The whole circumference of the Earth is about 24,000 miles and light can traverse that distance in about .1 seconds.
Thanks for the quick responses. Suddenly, I feel like it truly is a small, small world.
SSG Schwartz
Yeah, but your OP raises a very interesting question I’ve always had: If I can call Timbuktu with imperceptible, near-time conversations, why does the DSN phone lines (the military telephone system) always have that half-second delay between conversations?
I can’t tell ya how many times I’ve ‘talked over’ someone waiting for their response. . .
Tripler
I would think Uncle $am would have quicker telecommunications than DSN, unless he’s keeping it as a relic just for voice commo. . .
Maybe they’re using a geostationary satellite link? They orbit at about 24,200 miles. Double that is 48,400 miles which instills a one-way delay of about .25 seconds. Time to get a response back would be double that, in turn, or about .5 seconds. There may be a totally different reason for it, but the numbers work out. Anyone know for sure?
I’m guessing that the DSN is a satellite based system. In that case the light has to go much further than over the wires.
Thanks, Tripler, asking the other question I was wondering about. FTR the delay seems a lot longer than half a second and I am interested in the answer as well.
SSG Schwartz
That’s the way international calls used to be – in the 80s and earlier, there were plenty of satellite links in use for international calls, with the corresponding weirdness: not only was there the delay, but often times the call was half duplex, where either one could talk or the other could talk, but not both. I assume that fiber optic links have made the difference, beginning with TAT-8 in 1988.
When I spoke with family in Brazil many years ago, it really seemed like we were talking from several thousand miles away, and it was costly too. Nowadays, the same call to Rio sounds just like a call across town and is pretty cheap.
I make a lot of international calls. My experience is that you still sometimes get a call where there is a delay but mostly you don’t, and the number of times you do is decreasing. I’ve always assumed that this is because sometimes (presumably due to traffic or whatever) you get routed by satellite.
I meant to add: often, if you do get a call with delay, if you just hang up and redial, you get a line without delay.
Between 6-8 years ago, there would often be a delay when calling from India to Europe, but not only that: Often you could hear another conversation going on in the background of your own call. Surely this has nothing to do with the satellite link delay?
The continued use of geostationary satellites is part of the reason but the other part will be the speed of the electronic boxes converting from analogue speach to the the digital signal and back again. I don’t know the American DSN system but most military equipment is somewhat behind the times compared to consumer equipment and converter speeds have shot up recently.
Sometimes there is still a delay, albeit a minor one. As Tripler mentioned it seems like a 5 second or so delay. This was a recently as April. Dunno, you just get used to it.
This was cell phone, but not sure if it was military or civilian. I think it was civilian. Oh, but the damn minutes were military, that might make a difference, too.