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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."
This doesn't sound much better than armchair speculation either... Where are the real-world throughput benchmarks performed with actual equipment?
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.
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 802.11a access points _which have been "assosiated" with the 802.11g_) is rougly 1.5 to 2.5 times faster than 802.11b, depending on the type of collision-detection algorithm used.
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.
"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.
It's easy enough to upgrade everything to g-mode only.
Like iBooks? Like PDAs? Like wireless security cameras? There's more than laptops with PCMCIA wireless cards in the world.
"his article has real math based on the specs"
Kinda like judging a car's performance based on "real math based on the specs" when you can actually test the real thing in the Real World.
Whenever the offence inspires less horror than the punishment, the rigour of penal law is obliged to give way...
I think that not taking them alive was an unfortunate, but reasonable, alternative.
I used to be a cop, and did SWAT for about seven years... an assault on a fortified target like that is difficult in the best of circumstances, let alone in the midst of a hostile city, where you may or may not be able to guard your flanks. If that situation had turned into a prolonged siege, the brothers might have had the opportunity to contact local resistance elements, get some media attention, and shift the balance of that situation in their own favor, costing american lives. We already had multiple americans wounded in several attempts to make entry... how many more would have satisfied the critics?
An assault on a fortified target like that is very, very difficult, particularly when the occupants are armed to the teeth and unwilling to be taken alive. With a single stairway as a choke point, you'd have to attempt to breach elsewhere to gain a tactical advantage... nobody is going to want to advance into that stairway's "fatal funnel."
You would have to try to breach the ceiling (very hollywood, and not very practical in the real world), or breach one of the windows (thick, fortified glass). You could try to make entry from multiple points, or simply gunport those additional entry points... but you are talking about a prolonged, complex SWAT operation, something the military may not necessarily be set up to do, especially in that environment. You could try gas, but that doesn't always work. I've been on ops where we gassed the hell out of people, and they shook it off, even without gas masks. You could try the Russian "fentanyl" gas... might kill them anyway, and they'd be just as dead as if they were shot...
This operation was 101st, as I recall, and they are reasonably high speed. Don't get me wrong... the Delta/SEAL operators are the best, and their CQB skills are top-notch; I've trained with some of them, and I was impressed... but their mission and mindset are a bit different from a civilian SWAT team. They are soldiers in a war, not police officers, and their response in a hostile environment may not be optimal in a perfect world, but is certainly objectively reasonable considering the circumstances.
It would have cost lives, and valuable time to attempt to inject civilian SWAT tactics into that environment... I can certainly understand why they chose to do it the way they did.
They at least made an effort to take them alive... if I were that local commander, I wouldn't have squandered the lives of my men on two scumbags like Uday and Qusay either.
A trial and some iraqi justice would have been nice, but even so, they got what they deserved.
Even if a man chops off your hand with a sword, you still have two nice, sharp bones to stick in his eyes.
... that the 54mbits number measured how many bits fly through the air, not how many bits of the data you want carried from one end of the other. If it takes half the bits to guarantee delivery, then you still have a 54mbit connection, but only 27 of that is the data that you actually see.
Maybe I'm just used to marketing-ese. I remember when video game cartridges were measured in bits and not bytes. I remember being stunned that the Sega CD could store 4.7 gigs of data. Too bad I had to divide that number by 8.
Come to think of it, floppies were like that. "2 megs unformatted!"
Marketing really sucks for computer geeks. We want hard data, they want to give us the highest (or lowest) numbers. Go fig. This particular industry would do much better to appeal to practical #'s and develop trust based on that.
"Derp de derp."