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Master the art of wireless access point placement
stansbud@... - 01/29/03 Please read the original article.
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1. Interference with 802.11a???
stansbud@... - 01/29/03 You mention RF Interference with microwave ovens, cell phones etc. and 802.11a and 802.11g networks. 802.11b and 802.11g both use the 2.4Ghz space where this interference would be a problem. Isn't 802.11a interference free (for now) running in the5 Ghz spectrum?
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1.1. Possible Interference
Del Smith - 01/29/03 The 5-GHz band is unlicensed in the U.S. like the frequencies used by the 2.4-GHz technologies, but is much less crowded. So today, the probability of interference with an 802.11a network is much lower than 802.11b
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1.1.1. interference
amar_prus@... - 02/11/03 Interference is minimum in the 802.11a band leading to better speed.
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//RB
1.2. Another inaccuracy
killspam - 01/30/03 Also in the article, ?bringing the number of clients down to 15 or 20 will yield better network response (20 users for a 100-MB connection provides 5 MB each)?. There are 2 problems here; first, network speeds are in BITS not bytes. Second, the users are going through the AP, which is generally 11 or 54Mb, i.e. 20 into 11Mbps is close to 500Kbps. When you factor in wireless connections are typically 1/2 of the actual rated connection (i.e. it is extremely rare that you get 11Mbps connectionsto an AP), you get 250Kbps @ the client side...//RB
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1.2.1. Way off base!
the docman - 01/31/03 You're assuming that the bandwidth is shared equally by all users. As a CSMA/CA standard, the clients transmitting the most traffic will monopolize the most bandwidth, and when they go idle, they will use almost none. (It works much like the hard-wired Ethernet standards.)
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1.2.1.1. re: Way off base!
schnetman - 04/28/03 My statistics training leads me to suggest that a better estimate of bandwidth share is to divide the bandwidth by the square root of the number of users. So 11 Mbps shared between 10 people give aroun 3.5 Mbps each as a working average.
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1.2.2. You are right
Del Smith - 02/02/03 An edit was submitted to clarify this however it did not make it in time for publishing. Thanks for sharing this with the readers.
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Most often, a user is using the network to serve files and printers and web pages, and using ANY bandwidth less than 10% of the time. With that in mind, 20 users to an access point would be thoroughly reasonable and give performance in the same ballpark as having 1 user per access point, on average, as experienced by the user.
If your users are doing something different, like very frequently accessing and re-saving 5 Mb Powerpoints and/or accessing 700 Mb video files, that's different. But for garden-variety offices, it's a reasonable recommendation.
1.2.3. Yes, but...
Jeffykins - 09/25/06 It's very rare that office users use bandwidth continuously, unless they're seriously file sharing, which I assume you have turned off in your filewall.Most often, a user is using the network to serve files and printers and web pages, and using ANY bandwidth less than 10% of the time. With that in mind, 20 users to an access point would be thoroughly reasonable and give performance in the same ballpark as having 1 user per access point, on average, as experienced by the user.
If your users are doing something different, like very frequently accessing and re-saving 5 Mb Powerpoints and/or accessing 700 Mb video files, that's different. But for garden-variety offices, it's a reasonable recommendation.
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We added several 11a WAPs and upgraded most of our notebooks with 11a NICs, and now many of those users are begging for their 11b hardware back. The reliable range offers much more flexibility than the bandwidth. Only the folks near the break rooms (where microwave ovens were an issue)prefer the 11a.
Our next move is 11g.
1.3. Range vs. interference
the docman - 01/31/03 802.11a may be relatively clear, but unless you're dealing with a lot of newer cordless phones (or the occasional microwave oven)you'll probably find that the shorter effective range of 802.11a is a much more limiting factor than the interference inan 11b or 11g environment.We added several 11a WAPs and upgraded most of our notebooks with 11a NICs, and now many of those users are begging for their 11b hardware back. The reliable range offers much more flexibility than the bandwidth. Only the folks near the break rooms (where microwave ovens were an issue)prefer the 11a.
Our next move is 11g.
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AS far as range is concerned, you cannot expect to replace a "B" AP with a "A" AP. If you go with enterprise level access points like Cisco or Avaya, you will do better as far as throughput is concerned in general.
The 802.11 "B" runs at a maximum 100mW power output. The 802.11 "A" will run 40mW, 200mW, or 800mW depending on which channel you chose. There are 4 channels assigned to each power specification ( the 800mW is reserved for outdoor usage - Point to Point). Using the center 4 channels at 200mW will give you close to the renge exerienced with the "B" products.
I work at a school where there are large numbers of laptops in a small area. There are more frequencise available for 802.11A, which is an advantage in my environment. It is not uncommon for there to be 200 users in an area 150x150 feet (200 foot catchment area).
1.3.1. range and interference
edward.dennis@... - 11/10/03 There are 5 giga-hertz phones, but they use different frequencies ( a different band ) than the network AP's. The bands used by the "A" standard are, at least for now, reserved for networking, which should cut down on interference.AS far as range is concerned, you cannot expect to replace a "B" AP with a "A" AP. If you go with enterprise level access points like Cisco or Avaya, you will do better as far as throughput is concerned in general.
The 802.11 "B" runs at a maximum 100mW power output. The 802.11 "A" will run 40mW, 200mW, or 800mW depending on which channel you chose. There are 4 channels assigned to each power specification ( the 800mW is reserved for outdoor usage - Point to Point). Using the center 4 channels at 200mW will give you close to the renge exerienced with the "B" products.
I work at a school where there are large numbers of laptops in a small area. There are more frequencise available for 802.11A, which is an advantage in my environment. It is not uncommon for there to be 200 users in an area 150x150 feet (200 foot catchment area).
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The "A" standardalso has other interference factors: the new cordless phones in the 5.4Ghz range, and also Military Radar (around 5 Ghz).
The "G" in backwards compatiblity mode will go back to the "B" frequencies, so it is also a Access point congestion factor there.
Hopfully the FCC can get more frequencies from the UHF TV band ...
1.4. 802.11 a, b, and g interference.
kirk@... - 02/03/03 It is my understanding that the g standard (not yet finished by the FCC) starts in the 5 Ghz frequency range. So, the "G" is a type of interference factor to the "A" standard as a congestion (number of users) per Access Point.The "A" standardalso has other interference factors: the new cordless phones in the 5.4Ghz range, and also Military Radar (around 5 Ghz).
The "G" in backwards compatiblity mode will go back to the "B" frequencies, so it is also a Access point congestion factor there.
Hopfully the FCC can get more frequencies from the UHF TV band ...
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Military and air traffic radars come in two basic flavors, pulse and doppler. They operate in different frequency ranges depending on platform and purpose. Airborne search radars are in the 5GHz range, doppler weather radar in the 10GHz range, long range search radars in either the 2.4 or 5 GHz area.
All of these radar sets are encoded to prevent interference from other radars, and are often frequency agile also, thus using their entire assigned range. If you live near a major airport as I do (O'Hare) this overlapping radar coverage, plus heavy cell phone, wireless phone, radio, TV, CB, walkie-talkie and other uses make a real maze of frequency use.
Use of a spectrum analyzer to find (relatively) quiet bands is highly recommended!
1.4.1. More on Military Radars
jthomson60016@... - 09/02/03 kirk@barnescoputer.net wrote:Military and air traffic radars come in two basic flavors, pulse and doppler. They operate in different frequency ranges depending on platform and purpose. Airborne search radars are in the 5GHz range, doppler weather radar in the 10GHz range, long range search radars in either the 2.4 or 5 GHz area.
All of these radar sets are encoded to prevent interference from other radars, and are often frequency agile also, thus using their entire assigned range. If you live near a major airport as I do (O'Hare) this overlapping radar coverage, plus heavy cell phone, wireless phone, radio, TV, CB, walkie-talkie and other uses make a real maze of frequency use.
Use of a spectrum analyzer to find (relatively) quiet bands is highly recommended!
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Kurleigh Prescod
Spectrum Engineer
1.4.2. 802.11 clarification
kurleigh prescod - 11/10/03 Just to clarify kirk's statements, 802.11a operates in the 5.8GHz band, going from 5725MHz to 5850MHz. 802.11b and 802.11g operate in the 2.4GHz band, ranging from 2.4GHz to 2.4835GHz, and hence afford compatibility between the standards (that's why most cross-standard equipment offer b and g compatibility).Kurleigh Prescod
Spectrum Engineer
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2. Warehouse setup
AKJACKS - 01/30/03 I have been looking and hoping to find a similar article regarding an 802.11b implementation in a large distribution warehouse setting where you're having to deal with 5-high racks, open bay doors, and yaggie antennas. This setup is more complex and often requires constant tweaking as inventory levels and locations change. We have several site surveys done and we still are not where we need to be, but better than we were last year. What makes our environment unique is the fact we're using Telxon PTCs using TN5250 software to connect to our AS400 host via a WAN connection. This makes things a little more sensitive to time-out errors waiting for data. We have also seen some truck driver comm devices in the 2.4GHz range. Anyone have any experiences to share on this type of setup?
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2.1. Warehouse setup
WirelessFun - 02/10/03 I used a total of 16 Symbol model 4121 802.11b to give acceptable wireless access coverage in our 1+ million square foot warehouse. The wireless is for about 20+ forklift and cart mounted laptops (all office users are wired). In the section of thewarehouse with the dense 5 high racks I used 7 APs for coverage (this section is about 1/4 of the warehouse). The APs are all mounted on the 50 foot ceiling using 2 antennas each. The system replaced an old 900mhz system and performance is acceptable.
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Hope this helps...
Oh we chose 'B' networks vs. 'G' to gain the additional distance/gain.
FYI
2.2. Are you using WEP?
sda@... - 01/23/04 I know you "should" use it but we found significant performance losses with it enabled. We resorted to MAC filters and the like.Hope this helps...
Oh we chose 'B' networks vs. 'G' to gain the additional distance/gain.
FYI
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3. Range of WAP
heidan - 01/30/03 I was wondering where you came up with the 250 - 300 ft range. I have not been able to find any vendor data that show how far you can get away from a WAP and what the thru-put is.
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3.1. WAP Range
homestar - 01/30/03 Range in general is subjective. Cisco (and most other manufacturers) purports that their gear has specific patterns and ranges; of course these calculations are based on LAB and not real world. I have found the ranges to be about 1/3 less than reported by manufacturer as a general rule. All data from manufactures always come with disclaimer stating "you mileage may vary".
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3.1.1. Typical ranges
heidan - 01/31/03 So, what have you found typical ranges to be for 11a and b?
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As for bandwidth considerations, you can think of 802.11b as a lousy 5 mbit hub at best and 802.11g/802.11a as a lousy 20 mbit hub at best. Assuming all of your client cards are the same and they share evenly. If you use different type of cards, the stronger card takes the bulk of the bandwidth leaving almost nothing for the weaker and further ones. In the real world, more than 5 active users on an 802.11b AP gets to be almost unbearably slow.
For interference design, the most important thing to understand is channel selection. 802.11 b and g only has 3 non-overlapping channels, 1 6 and 11. You might be able to get away with slight overlap using 1 4 8 and 11. The nice thing about 802.11a is that it has 8 non-overlapping channels, giving much better overlapping yet non-interfering coverage. Knowing how to alternate channels to maximize the distance between the same channels and minimizing the distance between different channels is key to good wireless LAN design.
4. 100-150 feet is more realistic
georgeou - 02/02/03 In all my experience, 75 to 120 feet is much more realistic in the real world. Of course, actual range can vary from 50 to 300 feet depending on interference and obstruction, but 100 feet is pretty common.As for bandwidth considerations, you can think of 802.11b as a lousy 5 mbit hub at best and 802.11g/802.11a as a lousy 20 mbit hub at best. Assuming all of your client cards are the same and they share evenly. If you use different type of cards, the stronger card takes the bulk of the bandwidth leaving almost nothing for the weaker and further ones. In the real world, more than 5 active users on an 802.11b AP gets to be almost unbearably slow.
For interference design, the most important thing to understand is channel selection. 802.11 b and g only has 3 non-overlapping channels, 1 6 and 11. You might be able to get away with slight overlap using 1 4 8 and 11. The nice thing about 802.11a is that it has 8 non-overlapping channels, giving much better overlapping yet non-interfering coverage. Knowing how to alternate channels to maximize the distance between the same channels and minimizing the distance between different channels is key to good wireless LAN design.
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4.1. Range must be subjective.
redmonds@... - 02/10/03 I have one wireless user who is located 150 or so feet away from the WAP and he gets great throughput and there are several rooms (including an X-Ray machine if that matters) between him and the WAP. This was my first experience with Wireless and it has been a good one. I will slowly implement more wireless users into my LAN. Of course things will change once more wireless users come into play but range has not been an issue. I am using a linksys WAP-11 and a linksys WUSB11. needless to say, I'm impressed with it so far. Netspeed and the internet connection do not seem any slower than any of the other computers on the network.
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Nothing is "free"
4.1.1. Speed, too, is subjective
BBorden - 09/01/03 I installed a WAP in my home for my laptop. I noticed a slight speed reduction. I can document the reduction in internet speed compared to a wired connection to my 256/1.5 DSL router. I'm not sure how much if this is due to the encription time vs. the time for the extra hop.Nothing is "free"
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4.1.2. Type of adaptor makes a huge difference
Jeffykins - 09/01/03 I set up a friend of mine with a basement office and a teenager on the 2nd floor with 802.11b, with a single WAP on the 1st floor. In the basement there are two PCs: 1 with a D-Link PC card, and 1 with a USB adaptor (from SMC, I think). The USB adaptor (with diversity tuning) gets about twice as good reception as the notebook, almost all the time. I also experience very marginal reception with my notebook in my house: through two walls and a door, using a D-Link PC card and an SMC access point, I can get "No Signal" as close as 30 feet (!) from the WAP. Am I doing something wrong?
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Now, the brands I tried were wide-ranging in performance. Granted, this was when 802.11b first emerged, so manufacturers were still getting their act together. Here is what I found: Linksys cards were useless (others swear by them), D-Link worked, but very low signal strength (no matter where I was in relation to AP...even at 3 ft.), NetGear ruled, anywhere/everywhere, even outside in the parking lot. Since stores have better return policies, I used them to find the best solution. I tried several Orinoco (silver/gold) cards, and they seemed to perform well also. I'm glad that availability and prices have dropped for ext. antennas (for AP's/routers), and signal boosters. I just purchased a mini USB-type adapter(like the memory doo-dads), and have yet to test it. I liked the fact that it also comes w/ a 5 ft. extension cord, to elevate it for better reception.
I never noticed much of a slowdown by enabling WEP, nor MAC filtering. CHANGE the factory settings for SID, ALWAYS enable MAC filtering to keep neighbors/warriors out!!! But we are all pro's here, right??
4.1.2.1. Brands can differ too...
ninjamedic@... - 11/10/03 I had a 802.11b network set up in a single floor apt., with the AP in the LR, and my daughter in the farthest BR. It was only about 30 ft., but several turns in the hallway, walls, and the fact that her CPU was under the desk, against the wall, with a PCI/plug-in PCMCIA radio card. Due to the fact that I am a HAM, I am comfortable working with coax, connectors, cabling, etc., so I just built an antenna extension to get it up above the clutter. Due to the low power of these devices, I wasn't worried about acheiving a good ground plane, so much as I was sure of the correct wavelength of the antenna. This mod worked well. My daughter downloaded music like nobodys bidness (24/7), while my g/f and I streamed news/videos, music and software downloads (big) on 2 desktops (wired) and a laptop (wireless). None of us noticed any of the others slowing us down...amazing considering it was a Comcast cable connection.Now, the brands I tried were wide-ranging in performance. Granted, this was when 802.11b first emerged, so manufacturers were still getting their act together. Here is what I found: Linksys cards were useless (others swear by them), D-Link worked, but very low signal strength (no matter where I was in relation to AP...even at 3 ft.), NetGear ruled, anywhere/everywhere, even outside in the parking lot. Since stores have better return policies, I used them to find the best solution. I tried several Orinoco (silver/gold) cards, and they seemed to perform well also. I'm glad that availability and prices have dropped for ext. antennas (for AP's/routers), and signal boosters. I just purchased a mini USB-type adapter(like the memory doo-dads), and have yet to test it. I liked the fact that it also comes w/ a 5 ft. extension cord, to elevate it for better reception.
I never noticed much of a slowdown by enabling WEP, nor MAC filtering. CHANGE the factory settings for SID, ALWAYS enable MAC filtering to keep neighbors/warriors out!!! But we are all pro's here, right??
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4.1.2.1.1. Keep brand consistent
Kevj - 11/10/03 I purchased a D-Link wireless G AP/firewall. At a later date I purchased a Belken PC Card for my laptop. I soon found out that vendors implement the G standard in imcompatible ways. Hopefully, firmware/software upgrades will cure this problem in the future until all vendors implement the spec consistently.
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Questions:
1) Will another brand "G" repeater (if I can find one)work with everything else D-Link?
2) Will a repeater slow things down or mess things up for the other wireless users of the system that will be "seeing" both the source and the repeated signals?
3) Would a high gain (6 db) 2.4 (advertised for "B") antenna help much? And if so, would it be better to put it on the Access Point (where my other kids would benefit from it also - no one's got great signal strength) or on her PCI card?
4) My access point is the DI-624 rev B with two antennas. Would I need to get 2 hi-gain antennas for it and replace both if I went that route?
4.1.2.1.2. Where to put a hi-gain antenna?
Poordirtfarmer - 11/10/03 My youngest daughter's computer is in a downstairs bedroom on the floor against a far wall. The DI 624 (a D-Link "G" Access Point) is upstairs maybe 50 feet away. The signal level at her computer is absolutely zip using D-Links own DWI-G520 PCI card. My first thought turns to getting a repeater, but D-Link doesn't make a "G" version of repeater.Questions:
1) Will another brand "G" repeater (if I can find one)work with everything else D-Link?
2) Will a repeater slow things down or mess things up for the other wireless users of the system that will be "seeing" both the source and the repeated signals?
3) Would a high gain (6 db) 2.4 (advertised for "B") antenna help much? And if so, would it be better to put it on the Access Point (where my other kids would benefit from it also - no one's got great signal strength) or on her PCI card?
4) My access point is the DI-624 rev B with two antennas. Would I need to get 2 hi-gain antennas for it and replace both if I went that route?
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1)a repeater doesn't seem to make sense when the other computer is only 50 ft away from the ap. It sounds like you have something major blocking the signal. I've also found that the dlink wireless pc cards don't pick up wireless networks as well as some other brands (for cheap stuff i like linksys)...so the same may be true for their access points.
2.)i might try to install a second AP closer to the problem computer. Then instead of chances for problems, you would allow better coverage for all your wireless users.
3)if you use a high gain antenna on a G network make sure the antenna is designed for the network. A high gain antenna designed for B would certainly help increase signal strength but it might cause problems with communication - a wireless antenna is essentially precision tuned for the network it is designed for.
4)yes. If you replace one, replace both - diversity systems need to both have the same type/size antenna to function properly.
4.1.2.1.2.1. answers
hbchad@... - 11/11/03 My answers:1)a repeater doesn't seem to make sense when the other computer is only 50 ft away from the ap. It sounds like you have something major blocking the signal. I've also found that the dlink wireless pc cards don't pick up wireless networks as well as some other brands (for cheap stuff i like linksys)...so the same may be true for their access points.
2.)i might try to install a second AP closer to the problem computer. Then instead of chances for problems, you would allow better coverage for all your wireless users.
3)if you use a high gain antenna on a G network make sure the antenna is designed for the network. A high gain antenna designed for B would certainly help increase signal strength but it might cause problems with communication - a wireless antenna is essentially precision tuned for the network it is designed for.
4)yes. If you replace one, replace both - diversity systems need to both have the same type/size antenna to function properly.
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4.2. Slow bandwidth/terminal servers
Digi-Tal - 11/10/03 Is it me, or don't you leverage a terminal server for some of your 802.11 clients? The bandwidth being your major concern. Why not leverage the investment you have and serve screens instead of code? Maybe I miss the point but I have never considered mobile deployment for ALL of my clients, only those who demonstrate a NEED for access. (They tend to get spoiled otherwise)- 500 Things Every Technology Professional Needs to Know
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