nanog mailing list archives
Re: 60 ms cross-continent
From: Alejandro Acosta <alejandroacostaalamo () gmail com>
Date: Sat, 20 Jun 2020 15:55:58 -0400
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 aggregateSome 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 () gmail comOn Jun 20, 2020, at 12:44 PM, Tim Durack <tdurack () gmail com> wrote: And of course in your more realistic example: 2742 miles = 4412 km ~ 44 ms optical rtt with no OEO in the pathOn Sat, Jun 20, 2020 at 12:36 PM Tim Durack <tdurack () gmail com <mailto:tdurack () 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 () herrin us <mailto:bill () 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 Herrinbill () herrin us <mailto:bill () herrin us> https://bill.herrin.us/-- Tim:>-- Tim:>
Current thread:
- Re: 60 ms cross-continent, (continued)
- Re: 60 ms cross-continent Tim Durack (Jun 20)
- Re: 60 ms cross-continent Dave Cohen (Jun 20)
- Re: 60 ms cross-continent Mel Beckman (Jun 20)
- Re: 60 ms cross-continent Wayne Bouchard (Jun 20)
- Re: 60 ms cross-continent Saku Ytti (Jun 20)
- Re: 60 ms cross-continent Bryan Fields (Jun 20)
- Re: 60 ms cross-continent Martin Hannigan (Jun 20)
- Re: 60 ms cross-continent Saku Ytti (Jun 20)
- Re: 60 ms cross-continent Tim Durack (Jun 20)
- Re: 60 ms cross-continent Tim Požár (Jun 20)
- Re: 60 ms cross-continent Tony Finch (Jun 21)
- Re: 60 ms cross-continent Alejandro Acosta (Jun 20)
- Re: 60 ms cross-continent Joe Hamelin (Jun 22)
- Re: 60 ms cross-continent Rod Beck (Jun 22)
- Re: 60 ms cross-continent Carsten Bormann (Jun 20)
- Re: 60 ms cross-continent Marshall Eubanks (Jun 20)
- Re: 60 ms cross-continent Rubens Kuhl (Jun 21)
- Re: 60 ms cross-continent Brett Frankenberger (Jun 21)
- Re: 60 ms cross-continent Alejandro Acosta (Jun 21)
- Re: 60 ms cross-continent Rubens Kuhl (Jun 21)