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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
Gigabit ethernet is supposed to be 100 times faster than good ol' 10BaseT. It is, at the root layer. Most devices can't push that much data through the pipe, and with wireless, there is MUCH more error correction that needs to be done in communicating back and forth. Wired networks (normally) don't have the kind of interference that 2.4 GHz-band devices now suffer from.
When I said "armchair speculation," I was referring to the mass of articles that come out that talk about Wi-Fi speeds without actually looking at how the technology works.
Matthew has now provided a baseline. Someone could now perform real-world benchmarks against these theoretical maximums which are built into the standard.
Matthew's numbers provide optimal performance guidelines for network planning. Real performance will, of course, be even lower.
Freelance tech journalist for the Economist, MIT Technology Review, Macworld, and others
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.)
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.
However, when you connect a 10baseT NIC to a 100baseT switch, you don't slow down the rest of the connections to the switch, which can still operate at 100baseT. The situation with wireless, a shared medium, is more analogous to connecting a 10 baseT NIC to a 100/10 baseT auto sensing hub--when you hook up that 10baseT card, it slows down the rest of the hub to 10 baseT.
5.) It's still too slow to download Celeste-Virtual_BJ.avi in a reasonable time .GIF icons.
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
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.
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...
"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.
You didn't even look at the article, did you? There was no testing. The author didn't model TCP windowing at all, and he even failed to take delayed ACKs into account.
I have no complaints about the speed of my neighbor's wifi access point.
Strange women lying in ponds distributing swords is no basis for a system of government.
But 802.11 isn't full duplex.
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.
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...