本帖最後由 riceking 於 2020-11-18 09:42 編輯
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香港與貴州直線距離有900km遠，請問光子訊號傳輸而引致的遲延，要幾多時間 ...
slt 發表於 2020-11-18 07:11 
以理論值計算, Ignore介質延遲
光速大約300000km/s
延遲 = 1 / 300000 / 900 * 2 = 0.66 ms
現實啲就參考其他人嘅估算:
3. Distance
The biggest factor in typical WAN latency is the speed of light, through fiber-optic cable, which is about 124 miles per millisecond. A typical wavelength circuit within a metro area may travel from the data center to the serving telephone central office (e.g. 5 miles), then travel across the metro area on a metro fiber ring to another central office (e.g. 50 miles along a “beltway loop”), then travel to the destination data center (5 miles). The path will vary, depending on the local layout of your carrier’s fiber network, but a fiber path within a single metro area will usually be fewer than 100 fiber-miles in length. This should usually keep in-metro round-trip latency below 2 msec (fiber) plus 2 msec (electronics), or 4 msec., well within most clustering/application requirements.
To estimate latency of a wavelength between metro areas, take a look at your carrier’s proposed fiber route. Their fiber map is probably available on their website. An online mapping website can provide a rough estimate of highway distance between two cities, along the path used by your carrier. I’d recommend padding that distance by 10% to account for a few twists and turns at river crossings, freeway junctions, etc. To that estimate, add 100 miles for the local metro fiber path at each end, double the result (to get the round-trip distance), divide by 124 miles/msec, and add 2 milliseconds (for the electronics). For example, a Chicago/Dallas wavelength latency estimate might be:
925 miles x 110% = 1017.5 miles
+ 100 miles (Chicago local fiber) = 1117.5 miles
+ 100 miles (Dallas fiber) = 1217.5 miles
x 2 = 2435 miles (round-trip)
/ 124 msec/mile = 19.6 msec
+ 2 msec = 22 msec (electronics)
Ref: https://www.oneneck.com/blog/estimating-wan-latency-requirements |
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