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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."
When you connect a 10bT NIC to a 100bT switch you get reduced throughput.
EVERY medium that I've seen specs for published the actual bit rate of the wire/cable/fiber, not the end user throughput. They can't know that because they don't know what protocols you will be running over the network.
Article X: The powers not delegated... by the Constitution...are reserved...to the people
Even the manufacturers make this point. From apple's site:
If a user with an AirPort-enabled computer or a Wi-Fi certified 802.11b product joins an AirPort Extreme wireless network, that user will get up to 11 Mbps and the AirPort Extreme users on the same wireless network will get less than 54 Mbps. To achieve maximum speed of 54 Mbps the wireless network may only have AirPort Extreme-enabled computers on it.
Its not like this was quite the surprise its being made out to be...
You're special forces then? That's great! I just love your olympics!
(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 :):
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.)
Why is this billed as a bad thing?
For those who understand how this works, it is not a bad thing. However the hardware is being marketed to the general public.
As a result you can expect that people who see the 5 x faster than b are going to completely skip the small text that disclaims this on the back of the box. I think everyone would be surprised if this did not include a significant number of ostensibly technically inclined writers who will report that they did not see the improvements advertised, and who will subsequently give the technology a bad rap.
One fix for this would be to make APs that ran dual modes, but on different channels. For example 'b' on channel 3 and 'g' on channel 9. The AP would have to be able to buffer traffic between the two channels, but it would have to do so if it were acting as a repeater in any case, which I believe it has to to operate in both b and g modes.
I do not know if this is likely to happen, or is part of the spec already. If it is, then people should expect to see a significant performance boost.
-Rusty
You never know...
But 802.11 isn't full duplex.
Here are some real numbers.
Best Performance among various hardware
802.11g
wep off: 15.5Mbps
b card on network/wep off: 9.4Mbps
wep on: 10.3Mbps
802.11b
wep off: 4.8Mbps
Whenever the offence inspires less horror than the punishment, the rigour of penal law is obliged to give way...
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.