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As I understand it, some of the physical layer options for Ethernet include:\

10BASE5 (now considered obsolete): a single length of thick coaxial cable.

10BASE2: thin coaxial cable, of which multiple lengths can be connected by T connectors.

10BASE-T: twisted pair, of which multiple segments can be connected by hubs or switches.

Is there a reason why 'twisted pair instead of thin coaxial' has to go with 'connect segments with hubs instead of T connectors'? Something about the electrical properties of twisted pair that make it unsuitable for the simpler way to connect segments? Or is it just considered more convenient to use hubs or switches for other reasons?

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  • \$\begingroup\$ That's a very high level question. Why is star better than bus topology? Why is cat 5 better than coax? \$\endgroup\$
    – Passerby
    Nov 13, 2021 at 2:50
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    \$\begingroup\$ In a word, No. There's no reason you couldn't replicate the 10BASE5 or 10BASE2 topology using twisted-pair cables. Twisted pair cables and coaxial cables are two different ways of making a "transmission line." They have different characteristic impedances, but they obey all the same mathematical laws. The reason 10BASE-T networks use hubs and/or switches is because running cables from a central hub or switch is *MUCH* more convenient for the IT department than planning (and then later, changing) the route of a single wire that snakes all around a floor from workstation to workstation. \$\endgroup\$
    – Solomon Slow
    Nov 13, 2021 at 2:50
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    \$\begingroup\$ P.S., Don't ask me how I know. I'll tell you this time! I was that IT guy, dealing with 10BASE2, back in the 1980s. \$\endgroup\$
    – Solomon Slow
    Nov 13, 2021 at 2:52
  • \$\begingroup\$ @solomon the day some gen z or alpha tech makes a disgusted sound towards electrical based connectors I'm retiring. \$\endgroup\$
    – Passerby
    Nov 13, 2021 at 3:28

2 Answers 2

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There is nothing specific about coax (rg6) and cat 5 unshielded twisted pair that prevents the latter from working in a bus topology. The extra shielding in rg6 helps but the twisting in cat5 should do the same. Cat 5 can carry multiple bidirectional signals without issue. Ethernet hubs especially cheaper older ones without ICs are essentially a bus without the convenience of a single shared conductor. The benefits of a star cat 5 topology comes from switches, the reduction of sharing the common bus leading to higher bandwidth availability, material cost and in some ways weight. Duplex communication from the added conductors also speed things up. You also reduce the single points of failure.

The change from bus to star topologies is more to do about speed limitations than electrical properties.

In short, 10base-T doesn't require hubs or switches but they sure do make things better.

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Not particularly. Twisted-pair could work the same way, if you built a properly impedance-controlled 8P8C T-connector (which sounds a bit fiddly, but doable). But I don't think anyone really wanted that. 10BASE2 needs termination, one bad connection breaks the whole network, and adding a node requires rerouting cable to pass through the new T-connector, and temporarily disconnecting everyone in the process. Star topology is just administratively way less of a pain in the butt, and hubs weren't a high price to pay.

Plus, at any time you could replace a hub with a switch to reduce collisions and improve network performance, without pulling any new cable.

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