Hi All, What is the general rule of thumb when guestimating round trip time for new fibre installs? I'm particularly interested if anyone can reference any reliable source (not sure what that would be?) that gives a decent rule of thumb and why it is reliable enough to be usable given a reasonable error of margin;
I'm ordering a new single mode link to be installed between two PoPs in England with a radial distance of 31Km to each other, so for actual fibire length I would typically add about 35-40% to represent a likely worst case scenario [1]. So to calculate the delay I can say (c in meters per second); (c*0.6) * (31000*1.4) = (300,000,000m/s*0.6) * (180000000m) = 0.00024111111 seconds, or 0.24ms. I can safely assume that I would very likely get a 5ms RTT here. Infact I would likely get sub 1ms (usinig the latest hardware the control plane time for responding to a ping for example is microsends it seems, assuming queueing, encoding and serialisation delay of this link which will be 10GigE). Before this project could have even come to light if someone had said to me "Can you provide a link between these two PoPs that will have a latency lower than 2ms?" - Assuming all the above accurately relates to the real fibre properties I could say "Yes!" (subject to surveys, legel get outs blah blah blah). This project is already rolloing but I'm wondering what would others have quoted as a likely RTT for this example 31Km radial distance? Kind regards, James. [1] I know its perfectly possible the fibre route may well go via Timbuktu and back but in 95%+ of cases 40% extra distance covers it, in my experiance.
