I have a question regarding the round-trip propagation delay on an Ethernet network.
Page 123 of the Cisco Press "Designing Cisco Networks" book states:
"The most significant design rule for Ethernet is that the round-trip propagation
delay in one collision domain must not exceed 512 bit times, which is a requirement
for collision detection to work correctly."
With 100Mbps Ethernet, the maximum round-trip delay would be 5.12 seconds, resulting
in a distance limitation of 205 meters.
I currently oversee a large flat network covering several miles in diameter. All of
the links between buildings are single-mode fiber links. No routing is involved,
everything is switched - one large broadcast domain.
How does the 512 bit time rule apply to fiber optic cabling? I see on page 127 of the
same book that the Round trip delay in bit times per meter for Cat5 cable is 1.112,
whereas Fiber-optic cable it's 1.0.
I guess I'm having difficulty understanding how fiber can overcome the 512 bit-time
rule and can have a much longer distance.
I do realize that this is not exactly a Cisco question, though covered on the DCN/CCDA
material. If someone could kindly refer me to any material that covers this topic,
I'd appreciate it.
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