And thus far, no one has mentioned switching speed and other electronic overhead such as the transceivers (that's the big one, IIRC.)
I also don't recall if anyone mentioned that the 30ms is as the photon flies, not fiber distance. -Wayne On Sat, Jun 20, 2020 at 05:32:30PM +0000, Mel Beckman wrote: > An intriguing development in fiber optic media is hollow core optical fiber, > which achieves 99.7% of the speed of light in a vacuum. > > https://www.extremetech.com/computing/151498-researchers-create-fiber-network-that-operates-at-99-7-speed-of-light-smashes-speed-and-latency-records > > -mel > > On Jun 20, 2020, at 10:14 AM, Dave Cohen <craetd...@gmail.com> 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:> --- Wayne Bouchard w...@typo.org Network Dude http://www.typo.org/~web/
