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Four Simultaneous Access Points OK for 802.11b
jlouderb writes "ExtremeTech is reporting on a new analysis that shows that four of the 11 802.11b channels can actually be used simultaneously, rather than the just the three used today. This has big ramifications for multi-access point installations, especially in taller buildings. The analysis was done by the CTO of an 802.11b startup called Cirond and a white paper with all the details should be posted to their site later today."
"The analysis was done by the CTO of an 802.11b startup called Cirond and a white paper with all the details should be posted to their site later today.."
/. has anything to do with it ;)
Not if
"Hey! Unless this is a nude love-in, get the hell off my property!!"
Before anyone thinks that Europe is better because they have more useable channels, don't forget that our 802.11b channels have much larger asses than theirs.
Erik
YOU ARE SAYING IMPUDENCE TO ME! THAT IS IMPUDENCE!
Ask any map maker. You cannot tile a surface of arbitrary shapes with three colours. You need four colors. Since a WiFi channel acts as a map-filling color, the ability to use four channels gives real advantages. :-)
Well, it made sense when I thought of it.
Sig for sale or rent. One previous user. Inquire within.
Besides, if you want that many people on your network, 802.11b is not appropriate given it's slow link speed. I don't think 802.11b was ever meant to be the only netfrastructure in a commercial setting. My company uses it for conference rooms so the "important people" can bring their laptops in to waste everyones' time with presentations about schedules and upcoming meetings. :)
Putting any more than about 10 people on a wireless network in a "we're trying to do actual work" setting is suicide... oh wait, this guy was with a startup, they probably just use it to play Quake...
According to the article, the channel centres are seperated by 5MHz, yet the channels themselves span 27MHz.
Now, I'm probably missing something really, really obvious, but why don't they just limit the spread to, say, 2.4MHz from the centre? Surely that way all the channels (11 or 13, depending on where you are) could be used and you would still have a small buffer zone between channels?
Is is just that they can't make the frequency generators precise enough, or something?
Essentially, they are being "risky". A small section of overlap, in the weaker power section. I'm sure that they are not the only people to think of this. Certainly, they use of four aps does help cover an area more effectively, no question, and the diagrams do help show that :)
-- Who is the bigger fool? The fool or the fool who follows him? --
Using seven of the available channels was ranked as "sort of OK", nine described as "highly dangerous" and eleven of the available channels ranked as "marginally suicidal", by a team of highly trained hamster analysts.
If channel overlap is an issue where you are, you probably have too many damn AP's. Witness, rooms 424 and 417 of the EE building at Sydney University - two access points PER ROOM. Admittedly, they're large rooms (labs). I'm told that one is meant to be taken out of each and used elsewhere.
and the hundreds of RF engineers who have already spoken and said that only 3 channels do not overlap are still correct.
802.11b Channels are 22Mhz wide, and spaced 5Mhz apart.... grab a pencil and paper and figure it out. You can't get more than 3 channels without overlap.
The article lacks any real detail, other than a brief but accurate (typo aside, channel 1 goes to 2423MHz, not 2433Mhz) description of the 802.11b channel scheme.
One of the benefits of DSSS is that you can deal with interference to a good degree. If you use four channels, as widely spaced as possible, instead of three, you narrow your bandwidth, but not by too much. I imagine the overlap could be reduced to between 2Mhz for the end channels, and 4Mhz for those in the middle, possibly only 2 for those in Europe where the spectrum allocated is wider. Given how DSSS works, this may not affect data rates noticeably... this is what they are probably going to talk about in the alleged whitepaper.
Not sure why it's an article yet... there's no info yet.
Nothing annoys me more than the overly-precise. Let me take this point-by-point:
Yer right about the method by which the author asserts that the extra channel is made possible by addition of the third dimension (or third floor, in the least-case solution of his problem). But then you go and blow it with hyper-precision. Honestly, in this day and age, your "site survey" will very likely consist of a tech wandering around with a laptop looking at the signal meter. If the company in question is particularly anal, that tech might be actually carrying a notepad and perhaps an actual signal strength meter. Numerical modeling? Not likely.
Your second paragraph is predicated on the idea that the lan will consist solely of wireless. Again, not likely: not many people want to bother with replacing existing ethernet cards sitewide with 802.11 cards. More often, the wireless is for new computers and for laptop users, which is really a small proportion of all the computers in the building, no? As for myself, I have a wireless link in my office, which is fine for all sorts of "real work," and if for some reason I need to move big chunks of data, then and only then will I bother grabbing a 100-base-T link.
As to your third paragraph, utter hogwash. We have been very successfully setting up reasonably-sized labs with wireless-only networking for some time. It's really nice to do this when buying new hardware - what a dream when the only cable you need is power! (big hint here: try to find a cheap - US$750 with air, er, 802.11 built-in - computer, with a unix installed, and no butt-full of spaghetti sticking out the back. Give up? Think different) No problems. None.
"It's people like you what cause unrest"
political_news.c: warning: comparison is always true due to limited range of data type
...they don't get a patent on using that fourth channel ;)
<kiki>Stay good, cute lil' 802.11b startup! Stay good!</kiki>
Honey, I shrunk the Cygwin
I'm using 802.1sssjjjjssss;;;sjsfffeighbor insists that ''''ing the sa;e channesswill majjjjhe conn;;;ion stronger. Hessssery smart, don't you think?
political_news.c: warning: comparison is always true due to limited range of data type
There are so many nonsensical articles about what 802.11b can and can not do that I thought I'd set the record straight.
... well, sit down and draw yourself a map.
... I've seen DSSS signal quality go from excellent to unuseable just by flipping on a Cirronet AP in the same area.
There are eleven channels available in north america - 22MHz wide, spread from 2402 to 2483 MHz, with 5 MHz guard bands between them. Channels 1, 6, and 11 don't overlap, the others
There are many other things in 802.11b besides DSSS 802.11b cells that you 31337 kids can h4x0r - I've got Western Mux Tsunami and Adtran Tracer T1 bridges. T1s are full duplex - these types of radios split the ISM band 50/50 - one end sends with the bottom half and listens at the top, the other side is opposite, and they use 100% of the spectrum.
The other thing you'll find are FHSS systems in the ISM band. The most common is the Alvarion (previously Breezecom) Breeze Access II three meg access radios, but Cirronet's lower speed ISP products is starting to appear in rural areas.
If you're working inside a building with full duplex T1 bridges or a hot FHSS somewhere outside its definitely going to make a difference, and that goes double if you're running an 802.11b system outside. Putting one of these things near an 802.11b AP is basically like sand blasting a soup cracker
Assuming you've got no problems to deal with other than your 802.11b, other's 802.11b, and building layout you've still go trouble.
The 802.11b MAC layer is *broken*. If I pull up and start listening on a channel you're using, even if you've got WEP enabled, I can see your mac addresses and I can *issue disconnect requests* after forging your MAC and the AP *will honor the disconnect*. WEP is the equivalent of an ESP (encapsulated security payload) in IPsec and it protects your data, but the MAC layer needs something like the IPsec AH(authentication header) so that an intruder can't manipulate the MAC layer.
Building systems always have dead spots. Always. 2.4 gig bounces like crazy when there is sheet metal (HVAC duct work) is in the area. You get reflected signals (multipath) which causes corrupt frames, you get dead spots due to the signal being blocked, etc, etc. You can add further misery by trying to use an AP with 'diversity'. Drop the word from your vocabulary - its 'perversity' mode - just take the time to monitor FCS errors on an AP with this enabled and you'll know what I mean - turn that stuff on in a situation where both antennas can see the same signal and you'll toast 50% of incoming frames *every time*.
The 802.11b MAC layer is *broken*. If you want detailed knowledge I'd strongly suggest a read of the OReilly's 802.11 Wireless Networks book, but the game goes something like this. The channel you're in is a *shared* resource - that means you share with the rest of the world. 802.11b stations gain exclusive access to the channel they're on by settings a NAV (network allocation vector) in certain frames. Even if you have a WEP protected network the exposed MAC layer you're using will honor NAVs *from devices not on your network*. So when the same intruder who was disconnecting individual stations a few paragraphs back gets tired of that he can start issuing bent control frames that plug up the spectrum and bring your network to a crawl.
I've barely scratched the surface here. If you see a pretty diagram and a lot of marketing buzzwords, understand that the reality is much, much more grim.
I am very easy to get along with, but I don't have time to waste being nice to people who are being stupid. -Theo