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

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."

Comments

Re:Quick rundown: (corrected, mod this one up)

[dbarclay10]

(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 :)

Re:TCP model oversimplified

[pla]

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.