Ethernet – A reason why Ethernet has maximum cable length confuses me

cableethernetlayer1utp

The answer in this post suggests that it has two reasons.

While the impedance characteristics of a transmission line become less
favorable for high speed data as the line gets longer (resistance goes
up, capacitance goes up, the line is more susceptible to noise, etc);
however, the main reason Ethernet limits cable lengths to 300m is
because of time. … (Explanation of CSMA/CD)

However, modern Ethernet is operated with a switch, which eliminates collision between frames, and a need of CSMA/CD (CSMA/CD is no longer used recently)
For this reason, I think that more general reason is that it is because of impedance of a cable, which makes the signal weaker.
Which answer is more appropriate between two?

Best Answer

Which answer is more appropriate between two?

Certainly impedance, resistance and other factors are a consideration. However I would side with time.

Newer Ethernet standards include the capability for backwards compatibility. Devices can still operate in half-duplex mode and use CSMA/CD, and you can still buy devices today that only operate at 10Base-T (while these have become much rarer, I still see them installed from time to time - mainly building automation or industrial devices).

The infrastructure cabling also needs to continue to support all speeds, even down to 10/half.

There is a growing trend for some higher end network gear to no longer support 10Mbps data rates, but we are still quite a long way from dropping 100Mbps from the mix, and half-half duplex support is still required at that speed. Maybe some day time won't be a consideration, but for now it will continue to be to provide backward compatibility.