An 802.11n And Powerline Mess: A Hybrid Approach May Be Best

Continued from ‘An 802.11n And Powerline Mess: High Definition Video Distress‘…

Atheros developed the 802.11n silicon used in my Apple router and AppleTV, whereas Broadcom is the wireless IC supplier for my Dell XPS M1330 along with my Apple MacBook and MacBook Air. I spoke with both Atheros and Broadcom about my 802.11n performance problems at CES, and both vendors were baffled; although the standard isn’t yet IEEE-approved, the companies felt that the Wi-Fi Alliance’s interoperability testing still would have ironed out glaring bugs like mine. I invited them both up here (ideally at the same time) to do some on-site debugging, using the ‘carrot’ of nearby cross-country and downhill skiing as extra incentive. And after dealing with yet another sub-par HomePlug AV-based Windows Media Center Extender experience the other evening, I was highly motivated to dial in to a pre-visit teleconference with Atheros on Monday afternoon.

As part of my information download to them, I searched for the 802.11n driver version currently installed on the XPS M1330. Imagine my surprise when I found out it had a December 2006 publish date! An intensive search of Dell’s support site uncovered a (barely, but still…) newer version dated October of 2007, and after I installed it, the Network Performance Tuner plot jumped from below ‘acceptable for TV’ to around the ‘HDTV’ line. This begs the question of why a computer sold to me in July of 2008 still had drivers dated December of 2006 on it versus October 2007 replacements, and why neither Microsoft nor Dell’s programs intended to alert me to newer available drivers did their jobs…

The speed I saw wasn’t yet where I wanted it to be for reliable high-def video streaming, but in my excitement I decided to plunge ahead with the next step in my plan; getting the Xbox 360 on a wireless link, too. At the moment, I had the Xbox 360 and PlayStation 3 connected to each other and to the HomePlug AV adapter via a five-port switch, and I wanted to mimic this existing setup albeit without the powerline network portion. So I turned to D-Link’s DAP-1522, which merges 802.11n-to-CAT5 bridge and five-port GbE switch functions within a single device:

After configuring the DAP-1522 parameters to fit my router profile, I plugged the Xbox 360 into the DAP-1522 and powered on the D-Link device. The game console reported that it had a valid network connection, confirming that I’d correctly tweaked the DAP-1522 settings…

…but a subsequent Network Performance Tuner analysis reported that bandwidth was once again at sub-standard definition television speeds. Arrgghh! After a few minutes’ pondering, I realized what was going on. Realize first that, from an overall network topology standpoint, a single video stream coursing from source to destination is actually two streams; one going from the source to the router and through its integrated switch, and another heading out from the router to the destination. Whereas previously the stream coming into the router was using 802.11n while the outbound stream leveraged HomePlug AV, now both streams were contending for the same non-infinite wireless network resources…

…which was my second clue. My LAN contains a mix of 802.11n and 802.11g clients, so I was running the router in ‘802.11b/g compatible" mode. This meant that I was on the 2.4 GHz ISM band, and that I was only harnessing 20 Mhz-wide transmission channels. The former wasn’t particularly a problem, as I’ve got quite clear spectrum here. The latter was a bigger issue, from an overall performance standpoint. 802.11n’s other key advancements (besides the wide-channel bonding option), MIMO antennas (which are primarily beneficial at longer transmission distances) and frame aggregation, clearly weren’t enough to give me the speed I needed.

When I stumbled across a detailed DAP-1522 review, the final pieces of the puzzle fell into place. The DAP-1522, it turns out, has sub-par 2.4 GHz capabilities, especially in an 802.11b/g backwards-compatible network configuration. And it also suffers substantial bandwidth efficiency loss when TKIP encryption is in use. Per Apple documentation recommendations, I’d had the router in ‘WPA/WPA2 Personal’ encryption mode, which employs TKIP.

So here’s what I did (and as I write this, I still can’t believe I had to jump through all of these hoops):

• I migrated the 802.11n network to 802.11n-only, in the 5.8 GHz ISM band, with 40 Mhz (’wide’) channels. Ordinarily, the range reduction caused by the 2.4-to-5.8 MHz move would have been undesireable…fortunately, I live in a diminutive residence.
• I switched the encryption from TKIP to AES (’WPA2 Personal’)
• And for continued 2.4 GHz Wi-Fi client compatibility, I set up a Belkin 802.11g access point connected to the router (which also necessitated a migration from a five- to an eight-port switch).

Here’s the end result:

Better than before, but still marginal for high-def ‘Best’ quality content streaming. So believe it or not, while I’ve maintained the 802.11n link from the laptop to the router, I’ve returned to HomePlug AV for the router-to-game console portion of the chain, which got me back to here:

Keep in mind that the laptop is in the same room as the router, less than 25 feet away from it, and with line-of-sight proximity. The game console is also in that same room, and less than 15 feet away from the router. My conclusions, at least at this stage in the technology’s life cycle?

• 802.11n operating standalone (i.e. without the aid of another network topology to shoulder some of the traffic burden) is at best marginally capable of streaming high-definition video (and at that, only one source-to-destination stream at a time), depending on your codec and bitrate assumptions,
• In order to get 802.11n-based high-definition video streaming working, whether in a standalone or hybrid LAN topology, you’re probably going to have to discard any dream of 802.11b/g backwards compatibility, and.
• Vendors who are making wildly enthusiastically claims to the contrary (and you know who you are) are setting themselves up for a serious fall.

Thoughts, readers?

p.s..all this ‘one stream is actually two’ talk reminds me of Silicondust’s HDHomeRun, which I’ve mentioned before and which was on display again at CES this year:

Don’t get me wrong; I conceptually find the idea of a networked two-ATSC-tuner widget to be very, very cool. But practically speaking, I can only recommend a product like this to someone who’s got a LAN completely made up of 100 Mbps or (ideally) GbE CAT5, or alternately based on MoCA coax, especially if Extender devices are involved. I’ll leave you to do the math for various live TV-plus-TV recording-plus-prerecorded TV viewing combinations, but here’s the worst-case: watching two different live channels on two different Extenders with (by necessity) two different Media Center intermediaries translates to eight coincident ~20 Mbps streams coursing through a network’s veins.