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<p>Hello,</p>
<p> 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?</p>
<p><br>
</p>
<p>Thanks,</p>
<p><br>
</p>
<p>Alejandro,<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 6/20/20 1:11 PM, Dave Cohen wrote:<br>
</div>
<blockquote type="cite"
cite="mid:A2F6342A-5DC1-4B4E-9E05-BBF8F877A7FE@gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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:<br>
<div>- 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.</div>
<div>- 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</div>
<div>
<div><br>
</div>
<div>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. <br>
<br>
<div dir="ltr">Dave Cohen
<div><a class="moz-txt-link-abbreviated" href="mailto:craetdave@gmail.com">craetdave@gmail.com</a></div>
</div>
<div dir="ltr"><br>
<blockquote type="cite">On Jun 20, 2020, at 12:44 PM, Tim
Durack <a class="moz-txt-link-rfc2396E" href="mailto:tdurack@gmail.com"><tdurack@gmail.com></a> wrote:<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">And of course in your more realistic
example:
<div><br>
</div>
<div>2742 miles = 4412 km ~ 44 ms optical rtt with no
OEO in the path</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Jun 20, 2020
at 12:36 PM Tim Durack <<a
href="mailto:tdurack@gmail.com"
moz-do-not-send="true">tdurack@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Speed of light in glass ~200 km/s
<div><br>
</div>
<div>100 km rtt = 1ms</div>
<div><br>
</div>
<div>Coast-to-coast ~6000 km ~60ms</div>
<div><br>
</div>
<div>Tim:></div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Jun 20,
2020 at 12:27 PM William Herrin <<a
href="mailto:bill@herrin.us" target="_blank"
moz-do-not-send="true">bill@herrin.us</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px
0px 0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">Howdy,<br>
<br>
Why is latency between the east and west coasts so
bad? Speed of light<br>
accounts for about 15ms each direction for a 30ms
round trip. Where<br>
does the other 30ms come from and why haven't we
gotten rid of it?<br>
<br>
c = 186,282 miles/second<br>
2742 miles from Seattle to Washington DC mainly
driving I-90<br>
<br>
2742/186282 ~= 0.015 seconds<br>
<br>
Thanks,<br>
Bill Herrin<br>
<br>
-- <br>
William Herrin<br>
<a href="mailto:bill@herrin.us" target="_blank"
moz-do-not-send="true">bill@herrin.us</a><br>
<a href="https://bill.herrin.us/" rel="noreferrer"
target="_blank" moz-do-not-send="true">https://bill.herrin.us/</a><br>
</blockquote>
</div>
<br clear="all">
<div><br>
</div>
-- <br>
<div dir="ltr">Tim:></div>
</blockquote>
</div>
<br clear="all">
<div><br>
</div>
-- <br>
<div dir="ltr" class="gmail_signature">Tim:></div>
</div>
</blockquote>
</div>
</div>
</blockquote>
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