60 ms cross-continent

Mel Beckman mel at beckman.org
Sat Jun 20 17:32:30 UTC 2020

An intriguing development in fiber optic media is hollow core optical fiber, which achieves 99.7% of the speed of light in a vacuum.



On Jun 20, 2020, at 10:14 AM, Dave Cohen <craetdave at 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
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


On Sat, Jun 20, 2020 at 12:27 PM William Herrin <bill at herrin.us<mailto:bill at herrin.us>> wrote:

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

Bill Herrin

William Herrin
bill at herrin.us<mailto:bill at herrin.us>


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