8

If I'm using 10BASE-T, 100BASE-TX, or 1000BASE-T Ethernet on my home LAN and need to reach out to the internet, my modem will need to translate the routers LAN signals such that they can operate on coax over longer distances.

This new signal that is placed on coax - is it still considered Ethernet?

Improve this question
0

2 Answers 2

Reset to default
12

This new signal that is placed on coax - is it still considered Ethernet?

No.

Ethernet is a series of physical (various media) and data-link protocols (very few variants). The (obsolete) 10Base-5, 10Base-2, and 10Broad-36 versions of ethernet ran on coax. There are some special variants of ethernet that run on coax or other media for short distances, but the most common variants run on different standards of UTP and fiber.*

Cable modems use the DOCSIS (Data Over Cable Service Interface Specification) standard to run on a hybrid coax/fiber infrastructure.

*This answer, while not completely inclusive of all, lists many different ethernet variants, some of which are obsolete or only used in special cases, e.g. inside a device .

Improve this answer
4
  • 3
    There's actually 10GPASS-XR EPoC (IEEE 802.3bn-2016) - hybrid over coax and fiber - but I'm not sure whether that's in use at all.
    – Zac67 ♦
    Commented Nov 29 at 16:45
  • 3
    I have only seen DOCSIS used for cable modems. I would assume the IEEE standard would be only for ethernet, not on a commercial cable infrastructure that also carries video and audio as a service.
    – Ron Maupin ♦
    Commented Nov 29 at 17:19
  • 1
    @Ron-Maupin Our commercial cable is DOCSIS 3.1, but it no longer carries video and audio channels. And the last round of network hardware upgrade completely removed that capability from our cable head ends.
    – david
    Commented Nov 30 at 21:30
  • Also worth mentioning MoCA. While DOCSIS is usually used for ISP to customer last-mile connections, MoCA is usually used for networking over coax inside a home.
    – Shelvacu
    Commented Dec 2 at 9:08
5

Depends on which family of terminology you're considering.

At the physical layer: it's no longer Ethernet despite coax having superficial similarity with the media used by a 10BASE2 network.

At the data link layer: it might still use frames which are fundamentally Ethernet, i.e. have the same size limitations, checksums, and same way of indicating what the next-higher layer is. The details depend on whose cables and endpoint equipment are being used.

Improve this answer
14
  • 1
    @OrangeDog The typical home device called a "modem" isn't a true modem since it does not modulate and demodulate analog signals in the classic sense. DOCSIS is digital, so we normally wouldn't say that converting to and from Ethernet to DOCSIS is "modulating" or "demodulating"
    – Todd Wilcox
    Commented Dec 1 at 2:13
  • 1
    @ToddWilcox In fairness, OP didn't specify DOCSIS or any other specific encoding. "MODEM"- in its original sense- could potentially include modulation (or selection) of any carrier including DC, so basically you're throwing CODEC into the mix: the endpoint is a MODEM/CODEC/router/switch.
    – Mark Morgan Lloyd
    Commented Dec 1 at 8:03
  • 1
    @ToddWilcox Are you sure DOCSIS is digital? The references to QAM and OFDM look like analog sine waves to me. en.wikipedia.org/wiki/DOCSIS#Physical_layer
    – Nayuki
    Commented Dec 2 at 8:18
  • 1
    @ToddWilcox If that's the case, then 2.5, 5, and 10GBase-T NICs are "modems," as the transmitted signal is continuous amplitude, thanks to Tomlinson-Harashima precoding.
    – user71659
    Commented Dec 2 at 20:29
  • 1
    @ToddWilcox As I said, 2.5GBase-T and above uses a continuous-amplitude "analog" signal, so they're "modems" by your definition.
    – user71659
    Commented Dec 3 at 0:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.