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I’m trying to disentangle the common usage of the word “Ethernet”

I believe when people say 'Ethernet' they refers to 2 thing simultaneously:

  • a Protocol
  • a Transmission Line

That is when someone says:

"The data is transferred over Ethernet"

They are saying:

"The data is transferred over a LAN/MAN with Ethernet/Twisted Pair cabling using the Ethernet protocol"

Or would a more accurate definition be:

Ethernet = Ethernet protocol

. . . AND implies transmission over a LAN/MAN using Ethernet/Twisted Pair cabling

I know the Ethernet protocol is used over fiber optics also so, perhaps this definition is better:

Ethernet = Ethernet protocol

. . . AND implies transmission over a LAN/MAN

From my understanding, the Ethernet protocol is generally used only over LANs/MANs so the protocol implies the networks spatial scope by default.

(NOTE: I have read the Ethernet protocol can be used over WANs also, but Point-to-Point/HDLC is more common.)

And a bonus question: does 'Ethernet' generally imply a bus topology also? (I don't think it does, but worth asking nonetheless )

So, could you help me separate the words essence from its correlates. That would be very useful! Thank you for reading

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  • to bonus question: originally Ethernet was a CSMA/CD Bus. Since quite some time, no Ethernet standard uses a shared bus anymore. Ethernet uses switches interconnected by point-to-point links. They retain the original Ethernet header format, but nothing else from CSMA/CD bus. There are different Ethernet standards for physical media e.g., 1000BASE-T, 10GBASE-SR that specify various layer 1 issues.
    – Effie
    Sep 22 at 14:23
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That is when someone says:

"The data is transferred over Ethernet"

They are saying:

"The data is transferred over a LAN/MAN with Ethernet/Twisted Pair cabling using the Ethernet protocol"

This is not necessarily true. The term "Ethernet" is a victim of networkers' propensity towards overloading and/or abusing terms. If someone states that:

"The data is transferred over Ethernet"

then the safest interpretation (without further context) is that the data is transferred as the payload of an Ethernet L2 frame.

An Ethernet L2 frame does not have to be transmitted by an IEEE 802.3 PHY. For example, consider PPPoEoA as used over xDSL. The Ethernet frame is carried in ATM cells, which are then transmitted by the xDSL PHY.

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  • Hi Etienne, thank you for your clarification: "the safest interpretation (without further context) is that the data is transferred as the payload of an Ethernet L2 frame" Oct 7 at 19:41
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Ethernet is a family of layer-1/2 protocols that run on a variety of media, from the original coax bus to the latest fiber optics. Ethernet was created by Robert Metcalfe as a college project, and it is now maintained by the IEEE 802.3 working group. It has many different standards for various speeds on different media.

HDLC runs on the (almost) obsolete TDM circuits.

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Practically, all of the above.

Ethernet is a family of protocols. All of them use a common definition for the data link layer (OSI L2), with some variations. The numerous physical-layer variants (OSI L1) cover practically all use cases - twisted-pair copper for cheap, flexible uplinks (including single pair), fiber for medium and long reach interconnects, short twinax interconnects, and backplanes.

Ethernet started out as a (single) LAN protocol with very limited reach in the 1970s, inspired by ALOHAnet. It used a common wire (the 'Ether'), tapped into by each node, mandating half-duplex mode throughout.

Since then, it has considerably evolved, and most former restrictions have been either removed or vastly expanded on - speeds up to 400 Gbit/s and link reaches up to 80 km (officially) are readily available.

Today you can consider it as an almost universal protocol for LAN, MAN, WAN (MAN & WAN are fiber only), automotive (VAN?) and industrial applications. It has all but supplanted all the other WAN solutions except for xDSL.

does 'Ethernet' generally imply a bus topology also?

Its data link layer forms a logical bus (in that you simply send correctly addressed frames from a single interface and each one finds its way to its destination).

On the physical layer, nearly all modern variants use point-to-point links - no shared wire or media arbitration (CSMA/CD), no half duplex. Only the passive optical variants use a physical bus topology with TDM to share access for the uplinks.

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