60 ms cross-continent

Sat Jun 20 19:55:58 UTC 2020

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
> craetdave at gmail.com
>
>> On Jun 20, 2020, at 12:44 PM, Tim Durack <tdurack at 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 <tdurack at gmail.com 
>> <mailto:tdurack at 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 <bill at herrin.us
>>     <mailto:bill at 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
>>         bill at herrin.us <mailto:bill at herrin.us>
>>         https://bill.herrin.us/
>>
>>
>>
>>     -- 
>>     Tim:>
>>
>>
>>
>> -- 
>> Tim:>
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