Left segment - 450m, router, right segment - 180m.
Cable - 100Base-FX (multimode fiber - full duplex).
For such a fiber, the maximum length is 2000m, the delay by 1m is 1.0bt.

But when calculating the PDV I get:
PDV = 450 * 1.0bt + 180 * 1.0bt + 100 (2 FX adapters) + 140 (repeater of class 1) = 870bt

which is much more allowed 512bt. So, if fiber allows lengths up to 2km, then where was I wrong?

  • 1m delay - 1.0bt. Not confused, like 0.1bt per 1m. - pyatak
  • I don’t know, it’s written in all manuals that for Ethernet is 0.1bt, but since Fast Ethernet is 10 times faster, the delay is 10 times more for it. Thus, it turns out that the maximum segment length is 412 meters, but the fiber can be allowed up to 2 km. - palkanov-vi
  • No, not so. 0.1 is not for Etherneta, but for connections in which it runs namely in 100Base-FX, recalculate your formula by substituting 0.1 there. - pyatak
  • From 0.1bt everything is fine :) - palkanov-vi
  • Check everything up to the fiber, cable tester! It is possible that several connections in the cable (or connectors) have fallen off. - areshin

1 answer 1

The calculation is applicable in an environment with hubs ("class repeater ...") to prevent collisions. Thus, even with switches, this calculation cannot be used, let alone routers.