AFAIK when you wire a patch cable out of 5e, you only need to wire two of the conductors correctly for it to function as a ethernet cablebut you won't get gigabit ethernet.

However Homeplug uses your mains wiring which clearly only has 2 connectors and a earth wire.

Does home plug use the line conductor and netural as a pair?

  • 3
    \$\begingroup\$ Fancy RF DSP modem \$\endgroup\$ – Sunnyskyguy EE75 May 26 at 12:48
  • \$\begingroup\$ yeah, @SunnyskyguyEE75, but as an RF engineer, my channels aren't 100 Hz cyclostationary, with a solid amount of that cycle being unusable, and the farking frequency response of less terrible than in the Powerline comms channel. Also, in most cases I get the luxury of modeling noise as white – not so much with powerline channels. I honestly think that aside from very special applications, PLC is dead for anything that's not low-rate. I do not fondly remember my work on the PLC channel. \$\endgroup\$ – Marcus Müller May 26 at 13:23
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    \$\begingroup\$ To make things worse, @SunnyskyguyEE75, as an RF modem builder: your antenna's impedance changes not at all or worst case with frequency. you can statically compensate for that. A in-house grid's impedance a) changes cyclically, b) with the consumers plugged in and turned on and c) is rather low. \$\endgroup\$ – Marcus Müller May 26 at 13:30
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    \$\begingroup\$ There is a fundamental misconception in the question. A data connection is the only thing running on a category 5/6/7 cable, whereas Homeplug shares the cable with power. \$\endgroup\$ – David May 26 at 22:05

Remember how phone lines with a 64k modem in a 4kHz BW or 16bps/Hz had to be reduced to 56k due to FCC/EMI?

HomePlug AV only uses 917 of 1155 sub-carriers so each sub-band is like an audio FM channel that is equalized flat in that band with 4, 8 or 16 bps/Hz or so in each sub-carrier. The beauty of DSP power is to FFT and equalize so each small sub-band has a flat response. The latest standard supports 200 Mbps over home power lines.

ADSL and cable modems use a similar ODFM method, but much larger sub-bands.

So it's just a fancy RF Modem.


How many wire pairs you need depends on the design choices. It's always a compromise.

The design choices for Gigabit Ethernet are point-to-point, which guarantees a certain data rate, and simple electronics which makes it both possible to sell 8-port switches as cheap as 10€ and to have managed switches with 48 ports in a 1 HE 19" case at reasonably low power. In addition, Gigabit Ethernet is highly reliable.

This comes at the price of needing 8-lead Cat5 TP (Cat6 recommmended for some applications), which luckily happens to have been installed before for Fast Ethernet.

The design choice for »Homeplug«, »Dnet« is different. It's simply »no additional cables, no Wifi«, and you have to live with the consequences.

The price is a shared medium, which means the data rate is shared for all devices in the neighborhood, complicated electronics which are costly, huge and power-hungry, and unreliabilty, especially because the medium is also shared with nasty jammers as your mixer, power drill or vacuum cleaner.

  • \$\begingroup\$ In the case of Homeplug it is NOT considered a shared medium. Since there is a large number of channels available you could have multiple point to point Homeplugs and NOT have collisions (which is a very definite characteristic of shared media) and have the full bandwidth for each Homeplug pair. For example your home cable has lots of channels encoded on the same physical medium, but they do not collide since they use different frequency bands. \$\endgroup\$ – Jack Creasey May 30 at 23:46
  • \$\begingroup\$ It doesn't make a difference if you had time multiplex or frequency multiplex. It's a shared medium. All the devices share the common bandwidth. \$\endgroup\$ – Janka May 31 at 0:02
  • \$\begingroup\$ They do not share the bandwidth. A shared medium such as Ethernet CSMA/CD share the same space so the bandwidth used IS shared between devices. In a cable type media where multiple separate bands are used the speed within each band is NOT slowed by the use of other bands. See here: yourdictionary.com/shared-media-lan \$\endgroup\$ – Jack Creasey May 31 at 0:53

Does home plug use the line conductor and neutral as a pair?

Short answer, YES. The Homeplug devices use the Active and Neutral as a PHY layer medium. In the latest variant (Homeplug AV2) the line and earth can be used as a second pair to increase performance.

Can a Homeplug device send Ethernet down mains wiring?

Short Answer, NO. The Homplug device packages data received from an Ethernet port (the one on the device) into its own DLC protocol packets. It is NOT Ethernet over mains cable.

Your thinking of the problem is flawed, you need to consider the networking stack in totality to make any sense of the schema.

"Ethernet" is used in a consumer sense as a generic term, but there are a slew of standards involved. To start to break this out you need to consider the OSI stack:

enter image description here

Ethernet applies at the lowest 2 levels of the stack:

  1. At the DLC layer the standard defines a way to packetize data with an identifier for both the source and the destination points in a physically connected network. This has nothing to do with the physical network definition, for example the data could be sent over Coax using 10Base2 or Fiber using 1000BaseLX10 or over Cat 5 cable (probably what you consider to be "Ethernet") using 1000BaseT.
  2. At the Physical layer (PHY) the DLC frame of data is encoded for whatever means of transport is being used. This is a good explanation of the "Ethernet" PHY's

So to get to your misunderstanding. The Homeplug device DOES NOT in ANY WAY send Ethernet over the mains. The devices DOES present an Ethernet port, but the data from this port is split down to the basic layer two packet and re-encoded to be transmitted over the mains cable.
The modulation (or PHY) interface used by Homeplug devices has ABSOLUTELY NOTHING TO DO with Ethernet signaling, so don't think of it that way.

If you want to understand the HomePNA PHY interface you could start here.
As a hint to how to think of these networks of networks try to learn about MAC addresses (DLC, layer 2). In a Homeplug network the multiple devices must be able to distinguish (or be paired to create a virtual network) between endpoints. Homeplug take the pairing route so becomes a simple point to point network, but you could create a multipoint network under the the same HomePNA specifications.

As a really high level example, you could connect from your computer to a remote laptop computer on another continent. Your computer talks to a router/cable modem using an Ethernet port ….the remote computer is using WiFi. The two don't match, but you can talk. What happens in-between your computer and the laptop is unimportant and certainly is not Ethernet over anything. It's about protocol handling at OSI layer 2 and below.

If you want to understand more about the Homeplug networking architecture, read this introduction.


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