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HomePlug testing

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zzing123

New Around Here
Hi Tim,

Immediating repeating and mesh networking is supposed to be supported within the HomePlug spec, but I wanted to ask you when testing Powerline adapters, could you also test with 4 devices rather than just 2, to see if there's any tangible and improved benefit when reaching far away rooms?

The reason being is that I have 6 such devices, with 2 that are on ropey wiring. Despite this, these 2 locations (a garden shed and the attic) are still the best forms of connection I can get short of going exotic (dedicated radar dome) or expensive (actually lay a CAT7 cable), but I can only test on an absolute basis by running simple pings and benchmarks.

With your tools, I was wondering if in addition to the locations A through E that you test with, whether the existence of other HomePlug devices (same manufacturer/spec) improves performance in location E, and if HPAV devices are indeed smart enough to form a properly transparent mesh network or whether this part of the spec is just a fallacy.

In addition, if my assumption is correct that they do opt to use repeater mode automatically when it's a better connection, and with MU-MIMO, it should be the case whereby the HPAV devices optimise the whole network and decide which PHY 'route' is the most optimal.

The question I have is to do such optimisation, isn't some sort of methodology similar to OSPF or minimally spanning trees required to do this? But I can't see anything in the spec about this?

Anyway, I was wondering whether some digging and testing would be worthwhile to see if HPAV are actually a bit smarter than simple Point to Point devices?
 
The feature you refer to is Immediate Repeating, which is part of the HomePlug AV2 spec. From http://www.hindawi.com/journals/jece/2013/892628/

4.3. Immediate Repeating

HomePlug AV2 supports repeating and routing of traffic to not only handle hidden nodes but also to improve coverage (i.e., performance on the worst channels).

With HomePlug AV2, hidden nodes are extremely rare. However, some links may not support the data rate required for some applications such as a 3D HD video stream. In a network where there are multiple HomePlug AV2 devices, the connection through a repeater typically provides a higher data rate than the direct path for the poorest 5% of channels.

Immediate Repeating is a new feature in HomePlug AV2 that enables high efficient repeating. Immediate Repeating provides a mechanism to use a repeater with a single channel access, and the acknowledgement does not involve the repeater. As shown in Figure 22, station A transmits to the repeater R. In the same channel access, repeater R transmits all payload received from station A to station B. B sends an acknowledgement directly to A. With this approach, latency is actually reduced with repeating, assuming the resulting data rate is higher, the obvious criteria for using repeating in the first place. Also, resources required by the repeater are minimized since the repeater uses and immediately frees memory it would require for receiving payload destined for it. Also the receiver has no retransmission responsibility for failed segments.

I've reached out to an industry contact for additional input and will post if I receive any.

I can't see adding another node to the Powerline benchmark suite. But it could be worth a special article.
 
That'd be great. Didn't mean to insinuate you redo all historical benchmarks (unless the results are quite dramatic), but a special article would more than suffice.

The other thing is with MU-MIMO it seems to make much more sense to use many AV2 devices than just 2, as unlike wifi where clients and APs all utilize the 2.4/5GHz medium, power line is much more homogeneous in that it's only the adapters (save for noisy power warts) that utilize the mains as a medium.
 
Here is Broadcom's response:
The HPAV2 specification does include repeater functionality as an option. It is not mandatory.

We have had the software for 3-4 years but have not released it to production as we have not found any case where repeater functionality provides significant value.

For the US, if you trace the path from a socket on one circuit to a socket on another circuit, it has to go back to the breaker panel. So even if one has a room with excellent throughput and the adjacent room has poor throughput, the path traveled is no better then the direct path.

The solution moving forward is using WiFi/PLC with 1905 and Link Aggregation. This will be the preferred repeater technology moving forward as field tests shows excellent coverage throughout the home. Much better then PLC repeater technology.
 
Re US two-phase power ... Some (not me) contend that the RF will "leak" from phase A to phase B within 220V Romex type wires since they are in close proximity inside the same jacket.
my contention is that a 220V appliance that is ON (such as a cooktop or oven if 220) will hard-bridge. Maybe.
Otherwise, it's quite if'y, per me.

I read on some forum that the US National Building Code prohibits small-value (for RF) inter-phase coupling capacitors in the breaker box.

Though at KHz rather than high MHz, X10's signal historically had to get the benefit of a phase bridge to cover all the wiring in the house. X10 sold/sells a KHz-bridge (that might be forbidden).
 
While I appreciate for most of the world which use radial circuits, immediate repeating isn't really a big factor, here in the UK we like to be weird and different... and Broadcom's response is a little... shortsighted.

Firstly, we have enshrined in law that all buildings must be grounded. While this is common sense, it also means, handily, we can guarantee the use of MIMO in Powerline since there are always 3 channels.

Second, the UK's standard (and from our colonial past, a lot of Commonwealth countries still use the same plugs and wiring system, among a lot of other thing) is to use Ring circuits for better or worse (see: https://en.wikipedia.org/wiki/Ring_circuit). This means we basically have one mains wire going around the perimeter of the building supplying each plug. Of course we have several circuits, one for lighting, another for plugs and ovens and smoke detectors (!) have to, by law, have their own circuit.

Ring circuits, as opposed to Radial circuits like the ones you have in the US, are an entirely different topology to the 'solution' Broadcom is chasing, and while Powerline works absolutely fine on both systems, it would be good to see optimisations for both. In a ring circuit, when you have 4 or more devices on a ring, it's pretty obvious that Immediate Repeating is kind of essential.

Indeed that is exactly the case with my house. From any given device the two 'neighbour' devices connect and sync at a really high speed and have a benchmark graph as flat as a pancake. The 4th device, that has to bypass one or both of the other devices to talk to the diametrically opposite device, has a very choppy sawtooth benchmark profile and steadfastly refuses to sync at anything more than 200mpbs. The other 2 sync at 1040mbps and 860mbps.

I'm not sure how Immediate Repeating would work, but I guess it's something similar to WDS so I'd expect half the bandwidth - however given my devices are syncing at lovely super-high rates when they're friendly neighbours, half of a super high rate is still > crap rate.

So... I would like to see Broadcom be a little less shortsighted although with my devices (TP-LINK 8090's), it's actually QCA whose also seemingly not doing Immediate Repeating.
 
HomePlug uses many techniques that MIMO Wi-Fi uses, but conducted in mains wires vs. RF through the air. Any "blocking" that occurs is via contention for frequencies in use by other devices or marked as non-usable by PHY algorithms, not physical order in a circuit.
 

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