EDIT: You should probably ignore the individual test results below where the "office power strip was used".
Let's discuss these informal tests using HomePlug AV pair of devices around my 1800 sq. ft. townhome.
The devices are TRENDnet TPL-303E. These use an Atheros chipset that produces up to 200Mbps in the physical layer (PHY).
Geek diversion: The 200Mbps is the frame burst rate including bits for error correction and management that add overhead, as in any signal carrier communications - wired or wireless. The "modulation order" is the choice of how many information bits/sec to attempt to send in the channel's PHY. With weaker signals or interference, the PHY might still be at 200Mbps, but the information bit rate may have been reduced to cope with the poor channel.
So reducing the information rate to cope is like talking slower on a noisy/echoey phone connection to get the information through. Morse code (dit dit dah dah) is the epitome of this.
Other/newer HomePlug AV products increase the PHY bit rate to 500Mbps. But the transmission media stays the same, so to reap the benefit of this higher speed, the medium needs to have fewer impairments (as discussed below). In wireless, like WiFi, the same applies, but the impairments in wireless are far greater because the ether is very encumbered!
How this compares to MoCA (signalling over TV coax) is discussed later.
- Two rather fast PCs, each with a static LAN IP address
- PC #1 is a laptop connected to HomePlug AV device via ethernet
- PC #2 is a desktop connected to a gigE switch and to that switch is also connected a HomePlug AV device.
- Thus, the PCs and HomePlug devices communicate via the switch.
- Test throughput using "jperf", this being a iperf with graphs/charts.
- iperf in server mode on laptop that moves around; jperf on desktop to see througput versus elapsed time
First a baseline, connecting both PCs to the switch, no HomePlug devices in use. Just PC to PC via the gigE switch...
- One IP stream, one-way, 300KB TCP window size: about 900Mbps.
With the default smaller window size, (about 50KB) the throughput is of course much less. As expected, using a smaller window size, with many simultaneous streams from iperf, the aggregate speed approaches the 900Mbps capacity of the switch and TCP header inefficiency and Windows' TCP stack software overhead (which makes it hard to get to Gbps with real TCP traffic).
The next baseline:
Use the two HomePlug AV devices, but plug both into same power strip. Use a large TCP window size so that one stream can fill the capacity of the link channel.
- One IP stream, one-way, large 300KB TCP window size: about 70Mbps.
This seems to be the max; adjusting window size, etc, the speed didn't get above this number when using TCP.
Now to the tests with impaired transmission paths on the power line. The impairments are distance (wire length) and signal attenuation due to items plugged into AC outlets that have internal signal "sinks" for the HomePlug AV transmission frequencies. In lay terms, this is like pinching the water hose.
So we connect PC 1 and PC 2 to various AC outlets and measure each. Each pair of outlets "sees" different impairments to the other AC outlet. The impairing devices might include: GFI interrupter outlets, UPSes, so-called surge-protecting plug strips, major appliances, and so on. The closer the "sink" device is to the HomePlug device, in terms of in-wall routes of wires, the more of an impairment it is.
Another impairment is when the modem pair are plugged into different AC power phases (in a home with split-phase as in No. America). So outlet one runs to the breaker panel to a breaker tied to phase A, and the other outlet wires to phase B. In a home with 220VAC appliances, phase A and B run in the same jacket cable (romex if you will) and the high frequency signals tend to couple by accident from one phase to another. Some houses have no such cable (no 220V appliances). Some coupling might occur inside a 220V appliance). Ideally, and these exist, the breaker box has a phase coupler which connects the phases together with low impedance at the high frequency, but has no affect on the 60Hz power signal.
Bear in mind: Outlets in the same room can be on different circuit breakers. So the wire runs from outlet A and B may both go back to the breaker panel even though the outlets are in the same room. Or not. Perhaps they tie together in the attic in a J-box. Hard to say without a lot of dirty work.
Below, the outlet "Office plug strip" has a LOT of electronics devices plugged in: PC, router, switch, many wall warts, LCD monitor, etc. The data suggests that this is NOT the right place to plug in the HomePlug AV modem.
- PC 1 at Office plug strip. PC 2 at LR wall outlet shared with home theater stack of things. 1.5 - 2Mbps wow.
- As above, but PC 2 at LR outlet #2, on a different wall: 1.5 - 2Mbps
- As above, but PC 2 at kitchen counter outlet #1 4 - 5Mbps
- PC 1 at LR outlet 1; PC 2 at kitchen counter outlet #1 20-22Mbps
- PC 1 at LR outlet #3; PC 2 at kitchen counter outlet #1 20-22Mbps
- PC 1 at office power strip; PC 2 at LR outlet #3 15-17Mbps
- PC 1 downstairs bath wall; PC 2 at LR outlet #3 50-60Mbps
- PC 1 downstairs bath wall; PC 2 at Kitchen counter #1 42-45Mbps
- PC 1 downstairs bath wall; PC 2 at Kitchen counter #2 25-26Mbps
- PC 1 at office power strip; PC 2 at Kitchen counter #2 0.0Mbps, the modem's link light stayed dark, power cycle, stayed dark.
- PC 1 at LR wall #3; PC 2 at upstairs BR 1 40-43Mbps
- PC 1 at kitchen counter #1; PC 2 at upstairs BR 1 43-45Mbps
- PC 1 at kitchen counter #2; PC 2 at upstairs BR 1 40-43Mbps
- PC 1 LR wall #3; PC 2 at upstairs BR 2 17-18Mbps
- PC 1 office power strip; PC 2 at upstairs BR 2 4-5Mbps
- PC 1 LR wall at home theater; PC 2 at upstairs BR 2 10-12Mbps
- PC 1 LR wall at home theater; PC 2 at upstairs BR 2 at analog TV outlet 20-22Mbps
- PC 1 LR wall outlet #3; PC 2 at upstairs BR 2 at analog TV outlet 38-40Mbps
- PC 1 garage washer/dryer (120VAC) mach outlet; PC 2 at upstairs BR 2 at analog TV outlet 43-45Mbps
- PC 1 office power strip; PC 2 at upstairs BR 2 at analog TV outlet 28-30Mbps
Some pondering points:
- Office power strip plugged into outlet is on wall common to breaker panel in garage
- Home Theater outlet also has many signal sinks
- BR 2 is above office; short run to breaker panel
- One breaker in panel runs to all outlets near sinks/bath (builder put a single GFI outlet in garage, daisy-chained all wet area outlets to it. I guess GFI outlets were expensive in the 1980's when home was built.
So this is a bit anecdotal. But it's clear than the office power strip and/or the electronics items plugged in there attenuate significantly. I wanted to correlate lower throughput with where outlets are on opposite phases. But to do so, I have to look at the vague markings in the breaker box and/or flip breakers to try to determine what's on what phase. Need to do that on a rainy day when I'm home alone and don't mind resetting clocks and stuff.
Let's consider all this versus MoCA.
Of course, MoCA is viable only when there's TV coax at the two places to be IP connected. Like a home theater rig in a room where it's too hard to run CAT5. The other end would be on a TV coax outlet somewhat near the home LAN switch or router, or close enough to run cat5 to the MoCA device on that end.
Interference: A proper TV coax system, and choice of MoCA frequencies, would say there's negligible impairment from interference. The Power Lines for HomePlug may be interference free at the high frequencies, but there are notorious things like AC conducting- noisy switching regulators in electronics and wall wart power supplies, and the infamous light dimmers. Of course, one cannot operate the MoCA pair on the same frequencies used by, say, a satellite TV set top box to dish link, nor the same freqs used by a Cable TV set top box with its own MoCA for whole-house DVRs. A proper MoCA product finds unused frequencies automatically and allows the installer to designate the desired frequencies.
Attenuation: With MoCA, the attenuation is predictable: number of splitters n the path (beware splitter quality and high freq. ability); length of coax. Once planned, the attenuation won't change simply due to changing what's plugged in to various AC wall outlets as is the case with HomePlug AV.
Reflections: (Geek warning) The high frequency (OFDM) signals used by both HomePlug AV and MoCA are less subject to time-delayed reflections in the transmission media than non-OFDM. To be sure, there are certain conditions in either that cause a reduction in net yield throughput due to reflections. In HomePlug AV, this would depend on what outlet each is plugged into, and perhaps changing conditions due to what's plugged where in the AC outlets. With MoCA, reflections can occur due to crummy splitters or incorrect coax cable connectors, or coaxes left dangling (un-terminated). But these coax issues are fewer in number and can be viewed.
The test numbers say that HomePlug AV can provide the 30Mbps or more needed for HD TV 1080i streaming with margins, but it's not a willy-nilly plug and go. A test should be run to find if the throughput is too low and if so, one or both outlet sites need to be changed and re-tried. Then in the future, and this is the hard part, one needs to be mindful of plugging in signal sinks that may cause a speed reduction.
The MoCA case might be too complicated for the non-techie user, as planning is needed, whereas HomePlug is plug and go, lady-luck permitting.