Interoperability And Coexistence

When I asked Zyxel to send a pair of PL-100's for testing, they said that they would not work with the PLA-400. I thought that this was odd, so went directly to Intellon—the maker of the chipsets in both products—for confirmation. Intellon confirmed that while HomePlug Turbo would interoperate (connect) with HomePlug 1.0 products, HomePlug AV products will not interoperate with either earlier HomePlug technology. The reason was that they (the HomePlug Alliance, Intellon or both) did not want to "burden" HPAV with having to slow down to accommodate the slower devices.

Instead, HomePlug/Intellon opted to ensure that HomePlug 1.0, HomePlug 1.0 plus Turbo and HomePlug AV networks could peacefully coexist when used together in a typical home. This means, for example, that if you were already using HomePlug 1.0 or Turbo in your home and subscribed to a service that used HomePlug AV to distribute streaming content from a central set top box to slave boxes in your home, that both sets of connections would be able to work.

But as much as I like the rosy picture painted by the marketing folks, I ran coexistence tests to see how nicely the HomePlug family of technologies played together.

Figure 9: Powerline networking coexistence test setup

The three computers in Figure 9 were all set to different static IP addresses in the 10.168.3.X subnet and all adapters were plugged directly into outlets in my office lab (Location 1) . All adapters had default network passwords for the results shown. But I also did a quick run with different network passwords for the AV pair, with no change in results.

I modified the IxChariot script used for the throughput testing so that in one case I gave the PLA-400 test pair a 20 second head start in one case and the PL-100 the head start in the other. I also had both scripts send data from the IxChariot console to the remote endpoints instead of one receive and one transmit used in the performance tests.

Figure 10: HomePlug Turbo / AV Coexistence - Turbo first

Figure 10 shows that the HomePlug Turbo pair starts at ~27 Mbps. But when the HomePlug AV pair kicks in, Turbo throughput immediately drops to 10 Mbps, with the AV pair running at around 18 Mbps. This represents an approximately 63% drop for Turbo.

Figure 11: HomePlug Turbo / AV Coexistence - HPAV first

Figure 11 shows that the HPAV pair starts out at around 43 Mbps, but drops to the ~18 Mbps seen in Figure 10 once the Turbo pair starts running—a 58% drop. Note that while the IxChariot script starts the Turbo pair right at the 20 second mark, throughput takes a few seconds to ramp up.

The takeaway from this coexistence test is that it confirms that both HomePlug Turbo and AV networks can simultaneously operate without the destructive bandwidth battle I saw when I checked DS2 and HomePlug Turbo coexistence (refer to Figure 19 in the AV200 review). But the mechanism that allows Turbo and AV to coexist isn't very efficient, since both technologies give up about 60% of their normal throughput when running concurrently.