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Fast Wi-Fi's Slow Road To Standardization
CWmike contributes this excerpt from Computerworld: "For a technology that's all about being fast, 802.11n Wi-Fi sure took its sweet time to become a standard, writes Steven J. Vaughan Nichols. In fact, until September 2009, it wasn't, officially, even a standard. But that didn't stop vendors from implementing it for several years beforehand, causing confusion and upset when networking gear that used draft standards from different suppliers wouldn't always work at the fastest possible speed when connected. It wasn't supposed to be that way. But, for years, the Wi-Fi hardware big dogs fought over the 802.11n protocol like it was a chew toy. The result: it took five drama-packed years for the standard to come to fruition. The delay was never over the technology. In fact, the technical tricks that give 802.11n its steady connection speeds of 100Mbps to 140Mbps have been well-known for years."
I went through two small companies working on pre-standard N devices. Both went under as a little company you can't pre-run a standard to market. We were ready for production 7 years ago.
So yes, drama that personally affected me as I went through two collapsing companies.
The same thing happened with 802.11g. I remember going through four 802.11g PCI cards before finding one that could communicate with my 802.11g router at a distance of more than three feet. I was not aware that the devices were pre-draft (they didn't state "pre-draft" on the packaging like they do now), so I did not realize that was causing my problem. Eventually the standard was ratified, and if my memory is correct, the manufacturers released firmware updates so that the devices complied with the ratified standard. I doubt that this practice will go away since the manufacturers want to release bleeding-edge technology to stay ahead of the competition, but at least their packaging now states "pre-draft" so that cautious consumers will know to avoid it.
Basically any 802.11n system is going to be shit with legacy devices nearby. I believe this was one of the final barriers to standardization between Draft-N and final.
So to get decent performance you MUST be in the 5 GHz range. However, there are almost no 5 GHz 802.11n routers out there with external antennas! (Curse Linksys for their move to "saucer" form factors across their entire 802.11 product line... 100% driven by form and aesthetics/marketing, not technical function.) End result is that in most situations, a G router with an external antenna (especially an upgraded one) will blow nearly any of the 11n devices on the market out there.
retrorocket.o not found, launch anyway?
One of the tricks is low density parity check codes (LDPCC) which are the best currently known error correcting codes. They're decoded with a wonderfully elegant decoding algorithm which is embarresingly parallel so it works very well in hardware.
In fact, you can pretty much implement the belief network in hardware directly.
The codes are also used in 10G Ethernet, too.
Funny thing is that they date from the 60's, but were impractical because of the amount of computation required to decode them. The decoding algorithm was then rediscovered for inference on Bayes nets.
If you lick this sort of thing, it is worth reading Mackay's book on inference which is free online. I have no affiliation to Mackay, btw.
SJW n. One who posts facts.
Learn how to dress up the wiring nicely. It's a useful skill to have, and females appreciate quality nest-building in a mate.
That's an exaggeration. Here are real-world best-case-scenario speeds:
1 GB file
802.11b- 27 Minutes at 5 Mbit/sec (625 KB/sec)
802.11g- 8.5 Minutes - 7 Minutes at 20 Mbit/sec (2.5 MB/sec)
802.11n- 1 Minute, 15 seconds at 110 Mbit/sec (13 MB/sec)
100-BaseTX- 1 Minute, 30 seconds at 92 Mbit/sec (11.5 MB/sec)
1000-BaseT from/to Laptop drive- 17 seconds at 480 Mbit/sec (60 MB/sec)
1000-BaseT from+to high-performance desktop drive- 11 seconds at 800 Mbit/sec (95 MB/sec)
1000-BaseT RAM --> RAM - 9 seconds at 945 Mbit/sec (118 MB/sec)
60 MB/sec is realistic to expect when transferring to or from a laptop with a 5400 RPM drive. 85-95 MB/sec or even 100 MB/sec+ is achievable when transferring between high-performance 7200 RPM desktop drives, at the beginning of the drive.
However, 1 GB is small. A typical HD tv show is 1.1-1.4 GB. A typical 720p x264 encode is 5-8 GB. A typical 1080p x264 encode is 8-15 GB. A system backup can be anything from > 10 GB for incremental backups to 60-100 GB for full backups of system partitions.
At 85 MB/sec you can transfer a DVD (4.37 GB) in 60 seconds.