Thread: [Aironet] RE: RE: for consumer use
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From: Jonas S. <sa...@za...> - 2000-10-25 16:00:35
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Hi all! As one of these WLAN network builders, in Norway, I have to disagree with some of Elmers points: We have been using Aironet/Cisco for several years and there are some caveats with them. In contrary to what Elmer says, our experience is that the newer aironet units (802.11) is sensitive to noise. We have had cases where it was almost impossible to get the units to connect at all, we had to "yank" (disconnect/connect) the antenna connector several times to be able to connect. (I suspect some kind of AGC problem / saturation of the first RF stage...? We have reported this to Aironet several times, but have never gotten any feedback on the problem) When connected the link was fine, showing signal strenght of 80-95%, signal quality 90-100%. Running carrier tests to scan for other activity in the 2.4 GHz band showed nothing special, just 0-15% utilisation. Using a spectrum analyzer we found a quite strong signal at the site, at abt. 1.8GHz, probably GSM-1800. Ofcourse this trouble of establishing the link was unacceptable and we replaced the units with some older (non-802.11) units (2000-series) which were able to handle the noice. Other similar cases were replaced by Speedlan (www.speedlan.com) units wich also ran fine. We use mostly Speedlan now, they have a proprietary polling protocol much better suited for outdoor point-to-multipoint use, where one unit doesn't hear its neighbour, the "hidden node" problem. See their whitepaper on the subject: http://wavewireless.com/classroom/whitepapers/802problems.htm I suspect that their polling protocoll is the same as the one wavelan have on their outdoor "orinoco" products... I agree fully with Elmer in that it's better to use sectoral antennas, not omnis. The lesser noise the antenna picks up, the better. Omnis also generally have a really small E-plane opening angle, so where the terrain (or city landscape) is hilly, omnis are a bad choice. It's also a good idea to limit the output power level as much as possible, you dont want to clutter the frequency any more than neccessary, good for you AND the other users of WLAN equipment. However i disagree with the practice of using low-gain antennas for the customer. It's much better to use as high gain as possible, and lower the output power level. A 18 dBi antenna speads its signals over maybe 20 degrees, where a 2 dBi have an opening angle of maybe 180 deg., meaning that the frequency will be "polluted" over much larger area. Like Elmer says, go for small cell size, it's ,much better to have a number of small nodes , than one big one, if you can afford it. If possible, don't use 2.4 GHz to interconnect the node sites, find equipm. that uses 5.8 (lower output levels, but that doesn't matter for point-to-point links, as the antenna gain can be very high on 5.8 compared to 2.4 GHz), or use licensed bands like 18, 23, 26 GHz for the backbone. For the physical installation, allways use as short antenna cable as possible. You can NEVER win back what you loose here! (standard RG-213 antenna cable have a loss of abt. 0.5 dB/m at 2.4 GHz). Put the Radios in a cabinet at the mast if you have to, to get the cables short. It's much better to run 10baseT cables... Just my opinions, not neccessary the official policy of my employee! Vennlig hilsen/Best regards Jonas Sanamon --__--__-- Message: 2 Date: Wed, 25 Oct 2000 00:44:59 +0200 (GMT-2) From: Elmer Joandi <el...@yl...> To: Steve Creel <sc...@no...> cc: ai...@en... Subject: Re: [Aironet] for consumer access? On Tue, 24 Oct 2000, Steve Creel wrote: > We'd be wanting to use our wireless > network both for consumer access and wireless "leased lines". This makes sense if you have problems getting dsl lines for reasonable price, otherwise it is quite complicated and may not end with you and your customers being happy. > In all of > our dedicated circuit installations, we setup a firewall doing NAT amongst > many other things. My question would be this: from your experience, would > the aironet product line be sufficient for this type of application? depends. Wavelan has a special software for that, with which you can limit and guarantee bandwidth for customers. Hoverev, with proper topology, aironet is a bit better, it behaves better in noisy environments in 802.11 compatible mode. > What's a good number to figure on for the max radius of coverage > of a single bridge? [I take it that if I have two bridges with overlapping > footprints that they can communicate over their omnis?] > Is my thinking in the ballpark, > or am I just way out there? No, here around there are wireless networks in every city. However, I have been watching their progress and it is painful. Now it is even more, as local telecom has finally learned and starting come competitive with ADS being offered with 100$ + 35$/month, it becomes meaningless. But for last 4 years those network have been serving well. I have here small network on countryside and it is perfect. There is huge market for 802.11 in longdistance countriside links. But, in city, to be short, from my experience of seeing other peoples mistakes: 1. Do not make any central point. 2. make your APs with sector antennas AND separate uplink card. if there will be AP software for cards, it can be built into single 486, 2-4 cards, one of them uplink with directional antenna + sector antennas for serving clients 3. Do not install power nor powerful antennas at client site. It is real bad, if there will be one more ISP in your city, it will be nightmare. if you need to use powerful antenna, make it look a bit up, so the power will vanish into sky. Make it work so that it connects only "on the edge" install minimum power, if you are doing client installations. 4. put APs at high buildings on the border of city, or, if larger city, make clients allways to look from centrum to countryside and only point2point backbone links looking the other way. All people here have done otherwise and now redoing it. 5. If your real problem is your telecom not being flexible, then better talk to them and intrduce them to successful wireless WANs in eastern europe and in States too. Maybe they start being more flexible. 6. If you have a lot of money to invest, then make a 3 APs/km^2 network and clients with very small (2db) antennas. Or some 8dbi sector on client site and turn power down. Other side of it is that people can then walk on streets with their laptops. older 100mW aironets connect 1400m with 2 dbi antennas on both sides in relatively noise-free environments. So around 500m with 30mW cards and 8dbi antennas and power limited to 5-10mW at start would be a good bet. the cost of equipment for such a network would be about minimal 5k$/km^2 if to do it with cards. 7. On countryside, otherwise, use central desgin and average 5-8 km distance to client with max range about 15km 8. difference between bridge and AP, start with APs, you can reuse them anytime if your network grows. Besides, the HW is quite the same and _probably_ bridge soft will work later in those APs if you really need it. 9. Real cost for such a network with longstanding quality is 2 (not 1) radio kits(card, antenna, cables, processor(AP,computer) ) per client. 10. cabling, antenna and all small pieces make together a lot of money. The first salesman asks allways a double price. elmer. |
From: Elmer J. <el...@yl...> - 2000-10-25 16:45:30
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On Wed, 25 Oct 2000, Jonas Sanamon wrote: > In contrary to what Elmer says, our experience is that > the newer aironet units (802.11) is sensitive to noise. true, depends to what you compare. Note that mostly all of 802.11 of internal chips are made, AFAIK, in single factory and different providers only install different firmware and some part of radio. I compared to WaveLan, from the experiences of different people. You compared with old aironet, which was internally very stupid, but radio part was real good. > We use mostly Speedlan now, they have a proprietary polling protocol much > better suited for outdoor point-to-multipoint use, where one unit doesn't > hear its neighbour, the "hidden node" problem. See their whitepaper on the > subject: http://wavewireless.com/classroom/whitepapers/802problems.htm > I suspect that their polling protocoll is the same as the one wavelan have > on their outdoor "orinoco" products... yeah, funny that aironet has not implemented it yet. However, I say, if wavelan wants something 50-100$ per client for that software then it is nonsense. This polling software(which you could also emulate to certain extent with low RTS treshold) is a fake solution. It makes your problem to go to future. Only proper topology and distributed load will make it go away and then you dont need those expenseive pieces. What is SpeedLans price for that protocol and card alltogether ? > However i disagree with the practice of using low-gain antennas for the > customer. It's much better to use as high gain as possible, and lower the > output power level. A 18 dBi antenna speads its signals over maybe 20 > degrees, where a 2 dBi have an opening angle of maybe 180 deg., meaning > that the frequency will be "polluted" over much larger area. The cheapest, if to take this path, is probably 18-24 dbi connifer, turned a bit up. But, if you really want to build a serious city network, then it means that this technology should be used as it is ment to. It means 4-10 APs/km2 and lowgain client antennas. This is of course a different story if compared to todays problems, however, those networks may seriously kick UMTS in cities, as this technology is mostly available today, compared to UMTS 4-6 years. > Like Elmer says, go for small cell size, it's ,much better to have a > number of small nodes , than one big one, if you can afford it. If > possible, don't use 2.4 GHz to interconnect the node sites, find equipm. > that uses 5.8 (lower output levels, but that doesn't matter for > point-to-point links, as the antenna gain can be very high on 5.8 compared > to 2.4 GHz), or use licensed bands like 18, 23, 26 GHz for the backbone. Yeah, true, in States. We have here some airplanes flying on 5.8, some old soviet flight control radars and it is prohibited, but those look very sensible solutions for backbone. anyway, you can use high-gain antennas, if client site is under your control. If not, then they will raise power one day and it is real bad , if they all do. elmer. |
From: Elmer J. <el...@yl...> - 2000-10-25 17:11:04
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On Wed, 25 Oct 2000, Jonas Sanamon wrote: > where it was almost impossible to get the units to connect at all, we had > to "yank" (disconnect/connect) the antenna connector several times to be > able to connect. (I suspect some kind of AGC problem / saturation of > the first RF stage...? We have reported this to Aironet several I just recalled how someone here burned down 2 old aironets. He put antenna(connifer 24), on same tube with TV antenna. one connected to AP and then burned down after a while, the other burned right away. The problem was, that construction was not grounded and electric installation was bad, so some part of 220V come from TV and went into aironet. I dont know if it something about your situation, however, it would be very interesting to know, which theorethical protections there are against such a situation inside aironet new cards elmer. |