Hello,
Taking advantage of this thread may I ask something?. I have heard of
"wireless fiber optic", something like an antenna with a laser pointing
from one building to the other, having said this I can assume this link
with have lower RTT than a laser thru a fiber optic made of glass?
Thanks,
Alejandro,
On 6/20/20 1:11 PM, Dave Cohen wrote:
Doing some rough back of the napkin math, an ultra low-latency path
from, say, the Westin to 1275 K in Seattle will be in the 59 ms range.
This is considerably longer than the I-90 driving distance would
suggest because:
- Best case optical distance is more like 5500 km, in part because the
path actually will go Chicago-NJ-WDC and in part because a distance of
5000 km by right-of-way will be more like 5500 km when you account for
things like maintenance coils, in-building wiring, etc.
- You’ll need (at least) three OEO regens on that distance, since
there’s no value in spending 5x to deploy an optical system that
wouldn’t need to (like the ones that would manage that distance
subsea). This is in addition to ~60 in-line amplification nodes,
although that adds significantly less latency even in aggregate
Some of that is simply due to cost savings. In theory, you could
probably spend a boatload of money to build a route that cuts off some
of the distance inefficiency and gets you closer to 4500 km optical
distance with minimal slack coil, and maybe no regens, so you get a
real-world performance of 46 ms. But there are no algo trading sites
of importance in DC, and for everybody else there’s not enough money
in the difference between 46 and 59 ms for someone to go invest in
that type of deployment.
Dave Cohen
craetd...@gmail.com
On Jun 20, 2020, at 12:44 PM, Tim Durack <tdur...@gmail.com> wrote:
And of course in your more realistic example:
2742 miles = 4412 km ~ 44 ms optical rtt with no OEO in the path
On Sat, Jun 20, 2020 at 12:36 PM Tim Durack <tdur...@gmail.com
<mailto:tdur...@gmail.com>> wrote:
Speed of light in glass ~200 km/s
100 km rtt = 1ms
Coast-to-coast ~6000 km ~60ms
Tim:>
On Sat, Jun 20, 2020 at 12:27 PM William Herrin <b...@herrin.us
<mailto:b...@herrin.us>> wrote:
Howdy,
Why is latency between the east and west coasts so bad? Speed
of light
accounts for about 15ms each direction for a 30ms round trip.
Where
does the other 30ms come from and why haven't we gotten rid
of it?
c = 186,282 miles/second
2742 miles from Seattle to Washington DC mainly driving I-90
2742/186282 ~= 0.015 seconds
Thanks,
Bill Herrin
--
William Herrin
b...@herrin.us <mailto:b...@herrin.us>
https://bill.herrin.us/
--
Tim:>
--
Tim:>
