Interoperability And Coexistence
Although I knew that HomePlug and DS2-based devices would not communicate (interoperate) with one another, I at least hoped that they would somehow cooperate so that they could coexist when plugged into the same electrical grid. So I threw together the testbed shown in Figure 18 to find out.
Figure 18: DS2 and HomePlug Turbo coexistence testbed
The three computers in Figure 16 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. The two Netgear XE104 HomePlug Turbo adapters had their Network ID set to the default "HomePlug" and the two AV200 powerline adapters had their blank default Network IDs.
I modified the IxChariot script used for the throughput testing so that in one case I gave the AV200 test pair a 10 second head start in one case and the HomePlug Turbo 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 19: HomePlug and DS2 competing for bandwidth
(click image to enlarge)
Figure 19 shows that the two powerline networking technologies battle each other so that only one can operate at a time. The results I got over repeated runs were highly variable and would also depend on the distance between the various adapters. The bottom line is that the two technologies neither interoperate nor coexist without severly interfering with each other. This behavior was confirmed as expected by both Intellon and DS2.
I dinged the HomePlug Turbo folks for advertising 85 Mbps and delivering an average of 10, so let's see if DS2 does any better. Table 1 compares the % reduction from the advertised maximum throughput for the Corinex AV200 powerline and Netgear XE104 "85 Mbps" (HomePlug Turbo) for each of my five test locations.
Although the Corinex' best-case throughput of 65% is better than the Netgear's 71%, the other values are similar enough that DS2 deserves as much of a "shame on you" as I awarded to Intellon for selling high and delivering (relatively) low on throughput.
That having been said, however, it's clear that DS2's technology delivered consistently better performance than HomePlug turbo in my test environment.
|Location 1||Location 2||Location 3||Location 4||Location 5|
|Corinex AV200 Powerline (DS2)|
|Netgear XE104 (HomePlug Turbo)|
Table 1: Actual Throughput Reduction
from Advertised Maximum
The big question is why did DS2 design its technology so that it doesn't nicely coexist with HomePlug? It's not as if DS2 doesn't know what it takes to have its 200 Mbps technology coexist with both the installed base of HomePlug 1.0 and 1.0 plus Turbo products. After all, DS2 joined the HomePlug board at the beginning of 2004 (but at some point left both the board and HomePlug entirely).
What we have here is yet another case of a grab for marketshare using incompatibility with a competitive technology as a weapon. And, as usual, the consumer is once again thrown into the middle. Granted, that AV200 products aren't intended to be a big retail item. But consumers could be put into the position of having to throw out any HomePlug products they have when they sign up for an IPTV service that uses DS2-based powerline technology to distribute the service throughout a home.
As much as DS2 and HomePlug wish the other would go away, both are probably going to be around for the foreseeable future. HomePlug AV - which incidentally doesn't interoperate with HomePlug 1.0 and Turbo, but cooperates with them to share bandwidth - will eventually make it out of the labs and into consumer homes. Indications are that the HomePlug AV and DS2 technologies will battle each other for powerline bandwidth even more severely than has been shown for HomePlug 1.0 / Turbo and DS2. So all companies involved are going to need to confront this issue in a more constructive way or face consumer (and hopefully service provider) resistance.
Fortunately, the new leadership in the HomePlug Alliance seems to understand what's at stake and recently announced a new "compliance, interoperability and coexistence program". This initiative includes working with the IEEE P1901 Work Group and European Telecommunications Standards Institute (ETSI) Powerline Coexistence Work Group - the same groups that DS2 has been working with on the same issues.
The good news from all of this is that there is a powerline-based networking alternative that appears to be capable of supporting a few video streams and even some simultaneous good old data traffic to boot. Now if everyone would please just get along, maybe there will be room for everyone in the shiny, happy powerline-networked streaming video future, eh?