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When 54 Mbps isn't 54 Mbps: 802.11g's Real Speed

Posted by michael on from the compatibility-more-important-than-speed dept.

eggboard writes "Matthew Gast, author of 802.11 Wireless Networks, filed this article for O'Reilly Networks explaining exactly how fast 802.11g really is: that is, what's the actual data payload and real throughput, not the rated maximum speed. His conclusion? In mixed 802.11b/g networks, which will be common for years to come, g is only 1.6 to 2.4 times faster than b, not 5 times faster as it is in its g-only mode. This article has real math based on the specs, rather than armchair speculation."

6 of 127 comments (clear)

  1. Re:Quick rundown: (corrected, mod this one up) by dbarclay10 · · Score: 5, Informative

    (Sorry for the parent post, I made a typo. Just s/802.11a/802.11b/ in the second bullet point. "oops" :)

    Okay, I read the article, and here's a basic rundown (I think :):

    • 802.11g in a homogenous network (ie: only 802.11g access points) is faster than 802.11b (by a factor of five or so) and 802.11a (just a bit faster).
    • 802.11g in a heterogenous network (ie: some 802.11g access points, and some 802.11b access points which have been "assosiated" with the same network as the 802.11g access points) is rougly 1.5 to 2.5 times faster than 802.11b, depending on the type of collision-detection algorithm used. This setup is not as fast as 802.11a.

    So, to sum up the summary: If you start replacing your 802.11b access points with 802.11g access points, you'll see some performance gain with 802.11g client devices right away. When all your 802.11b client devices are gone (and thus all the 802.11b access points), it'll be way faster. Faster even than 802.11a.

    Why is this billed as a bad thing? You get compatibility with your existing infrastructure, a little bonus performance now, and when the time comes, bang you get a big boost.

    This is the kind of thing that sysadmins such as myself LOVE :)

    --

    Barclay family motto:
    Aut agere aut mori.
    (Either action or death.)
  2. Maybe I just can't summon the righteous anger by chriso11 · · Score: 5, Insightful

    Oh, so I only get a 60% faster connection? Given that soon enough the price differential between B & G will be gone, I still think G is the superior choice. When the wireless cards are only $15 to $20, I think that pure G networks will be much more common. And then you will get much higher throughputs.

    Maybe they should go after Dannon yogurt for decreasing the size of their container to 6oz from 8oz, but keeping the price constant. Then at least they would be reporting on something I could care about.

    --
    No, I don't trust in god. He'll have to pay up front, like everybody else.
  3. Top 5 Reasons to Avoid Wireless by Amsterdam+Vallon · · Score: 5, Funny

    5.) It's still too slow to download Celeste-Virtual_BJ.avi in a reasonable time
    4.) You're not a cafe communist with a computer and a four dollar cup of coffee.
    3.) The low-bandwidth version of Slashdot doesn't have those cool 1997 .GIF icons.
    2.) The babes dig retro shit these days, like 14.4bps dial-up.
    1.) Your life revolves around physical things, not six-hundred dollar mp3 players (iPaqs, etc.)

    --

    Reply or e-mail; don't vaguely moderate. Ex-O'Reilly/MIT employee, now a full-time Google employee.
  4. TCP model oversimplified by kuknalim · · Score: 5, Insightful
    I stopped reading the article when i got to this:

    "Furthermore, the model ignores the sophistication in the TCP acknowledgement model. To avoid constraining throughput, TCP uses "sliding windows" and allows multiple outstanding frames to be transmitted before acknowledgement. In practice, TCP acknowledgements can apply to multiple segments, so this model overstates the impact of higher-layer protocol acknowledgements."

    This reduces the "TCP" he uses to a stop-and-wait protocol.

    1. Re:TCP model oversimplified by pla · · Score: 5, Informative

      This reduces the "TCP" he uses to a stop-and-wait protocol.

      Unfortunately, I have no mod points, but I really wish I did so I could throw one your way.

      Apparently, of all the supposed techies reading the article, only you caught that problem (hey, I'll admit it, even I glazed over on the details, so kudos to you). And that one change of his TCP simulation makes ALL the difference - If you take out all the part of a protocol that make it play well in a multiple-speed in-and-out environment, then yes, in fact, it will behave only slightly better than the worst speed in any direction. Almost a trivial statement, yet the parent post's entire premise rests on this one idea.

      Sad. And again, kudos, good catch.

  5. Re:Quick rundown: (corrected, mod this one up) by ShadeARG · · Score: 5, Funny

    Holy ballz son. You've discovered a new formula!

    1) Post Insightfully with format errors
    2) Admit to mistake and repost with corrections
    3) Go from Insightful to Informative and reap in double the karma

    Niiice.