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#81
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Canon 6D
In article , Floyd L. Davidson
wrote: you didn't know what automatic meant and you think all base stations have vertically polarized antennas. I certainly don't know what *anything* means to *you*! it's what the industry defines it as, not me. *they* are the ones calling it automatic. stop trying to weasel out of it. And yes, virtually all base stations ahve vertically polarized antennas. previously, you said all, now it's virtually all? hilarious. not that it matters. it's nowhere close to 'virtually all.' travel routers, for example, are polarized in whatever orientation they happen to be when used, particularly the battery operated ones, such as a cellular mifi device. having the selection be automatic spreads it out, without the user having to figure out what to do. not everyone is a geek. most aren't. even many of those who are geeks probably don't know what to pick. All it has to be is a default to an "auto" mode that switches between only three channels unless some other option in chosen. Simple, easy... except when that doesn't work. What do you mean it does't work? It would work far better than randomly picking just any channel. except it's not random. Sigh. I drew a graphic and made a chart previously that showed *precisely* what the channel separation is. The simple fact is that yes it will increase interference if you choose anything else. it will not increase anything. Just interference. nope. |
#82
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Canon 6D
nospam wrote:
In article , Floyd L. Davidson wrote: you didn't know what automatic meant and you think all base stations have vertically polarized antennas. I certainly don't know what *anything* means to *you*! it's what the industry defines it as, not me. *they* are the ones calling it automatic. stop trying to weasel out of it. I merely asked exactly what you meant, since *you* didn't have the sense to explain yourself. That is hardly trying to weasel out of anything. In fact we were talking about a client automatically changing channels to match the AP, and when you said the AP could be automatic is certainly made me think you were saying the AP adjusts to the client. That doesn't make sense, so I simply asked what you meant by "automatic". Pretty reasonable... but you aren't. And yes, virtually all base stations ahve vertically polarized antennas. previously, you said all, now it's virtually all? hilarious. Same thing. You probably don't know what the significance is anyway. Of course many if not most units have always had antennas that can be adjusted. They *all* recommend using vertical polarization, but there are good reasons to use horizontal in some special circumstances (mostly to restrict the range). not that it matters. it's nowhere close to 'virtually all.' travel routers, for example, are polarized in whatever orientation they happen to be when used, particularly the battery operated ones, such as a cellular mifi device. And any instructions that mention antenna orientation will say to position the unit in a way the results in vertical orientation. Again, that is because vertical *is* the standard (for very good reasons), and will generally produce the best results. In the case of a direct line of sight with no multi-path there is about 30 dB loss from cross polarization. I haven't seen the insides of some of the smaller WIFI units for cameras and similar devices, but I would guess that at least some of them use circular polarization, just to avoid excessive loss from cross polarization. Sigh. I drew a graphic and made a chart previously that showed *precisely* what the channel separation is. The simple fact is that yes it will increase interference if you choose anything else. it will not increase anything. Just interference. nope. Ignorance is bliss, and you seem blissful enough. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
#83
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Canon 6D
Floyd L. Davidson wrote:
Wolfgang Weisselberg wrote: Floyd L. Davidson wrote: There will never be a time when at least 10 or so clients are not trying to get access. And that's lowering the individual thoughput by a factor 400? (WLAN netto speed, single user, 54 MBit/s brutto versus dialup modem brutto speed of 33.6 kbit/s upload) Yes. When none of the clients can get a connection, due to repeated contention, there is *no* throughput for any client. You're of course completely right ... .... if there WERE no way to make a connection, there WOULD BE no throughput. Unless one of them has a received signal strength that is more than 6 dB greater than the sum of the others, the AP cannot detect a single client. The way it works: Stations listen if the channel is free, and have random timers (the more collisions, the larger) which cause most packets to not be involved in a collision. (It's actually more complicated than that, but read yourself ...) http://www.comlab.hut.fi/studies/324...ot/4_wlan2.pdf The upshot is: There's no "the sum of the others". Yes there is. Now do some research on something called "capture effect" with FM or PM modulated radio signals. The capture effect sort of requires that at least 2 nodes are sending simultaneously, true? What happens if this situation is mostly circumvented --- like in WiFi, where (see link above) extreme pains are taken to avoid this sort of thing? Or are you talking about radiation from other sources, in which case WiFi won't work even with a single client? The functionality is on several levels, not just WIFI contention. There are also colisions between clients transmitting at the same time. Of course. In which case they'll detect that there has been a collision as they don't get an ACK, increase the limit of their CW_{backoff} and back off more. If the AP has an RSL for one client that is 6 dB or more above *all* other signals in the desired bandwidth, that client will be accepted, otherwise the AP will not be able to detect a usable signal from any of them. True. Just not as common a problem as you make it out to be. Just like dropping your camera during a studio assignment and it breaking *is* a real problem ... In fact, even with a CW_{Backup} of only 32 (i.e. set for rather few collisions, it can ramp up to 255) the chance of collision is 50% with 16 active stations and 63% with 35 active stations.[1] No answer? So none of them get a connect, they all time out and take a random sleep. Only one will talk, and in most cases it will get through. And if not on the first try, then on the second, third of fourth. Wrong. Whatever makes you think "only one will talk"! Every time there is a collision, the entire process essentially starts over again. A collision only happens when both sides start talking at the same time. If one already started, in your PJ case all other WiFi-nodes pick up the fact that someone is talking and remain silent.[2] GOT THAT? The chance for 2 or more nodes to send at the same time means that their microsecond timers must pick identical values. The chance of 2 nodes having the same timer set is p_{collision} = 1 / CW_{backoff} The chance that the second node does NOT have the timer set to the same value is p_{no collison} = (CW_{backoff} - 1) / CW_{backoff} So for CW_{backoff} == 7 the chance for 2 nodes would be 6/7 for no collisons. For 3 nodes it would be: p_{no collison} = (CW_{backoff} - 1) / CW_{backoff} * (CW_{backoff} - 1) / CW_{backoff} = ( (CW_{backoff} - 1) / CW_{backoff} )^2 For n nodes it is: p_{no collison} = ( (CW_{backoff} - 1) / CW_{backoff})^(n-1) and p_{collision} = 1 - p_{no collision} = 1 -( (CW_{backoff} - 1) / CW_{backoff})^(n-1) Given n = (48 PJ + 1 AP) = 49 (i.e. all 48 on one single channel, all wanting to talk NOW): CW_{backoff} p_{collision} in % 7 99.94% (typical lowest value) 32 78.2% 64 53% 128 31% 255 17% (max value) Now, given that only a completely incompetent person would offer only one channel: n = (48 / 3 PJ + 1 AP) = 17 CW_{backoff} p_{collision} in % 7 92.73% (typical lowest value) 32 42% 64 23% 128 12.4% 255 6.44% (max value) That's simple probability calculus. The chances never get any better. Wrong, CW_{backoff} is raised through collisions. Go try yourself: roll one black and 4 red 6-sided dice and see how often the black and any red dice have the same number. Now repeat that with the same number of 20-sided dice instead! And for kicks, try with 1 + 16 32-sided dice (your PJ-example, 3 channels, CW_{backoff} = 32) and with 1 + 16 *255*-sided dice (same, but CW_{backoff} = 255). You are assuming that all clients can detect all other clients, which is probably not true. In your PJ at a press conference case, it very probably IS true .... and then there *is* RTS/CTS for hidden nodes. Of course by that time another group is ready (after waiting for a random period), and the story repeats itself. Yep, all the group of 10+ clients has each RANDOMLY choosen one and the same period of time --- and will do so every time! That's why it's called RANDOM! And that is exactly why if fails too. It doesn't fail. Sure, you _could_ build a token ring wireless network. However you can't use token ring for nodes that try to connect, as they are not yet in the ring ... and if there are 2 nodes waiting, they'd *always* cause a collision that way when sending the token to "any new node". With random they only cause a collision *sometimes*. In addition, nodes dropping off the network (switched off, getting out of range, ...) cause a token to be dropped. Since you want high bandwith and care a bit less about latencey, not (sorta)-guaranteed latency (for a given, unchanged node group) and low bandwidth, token ring's not the right solution Eventually luck might allow one client to connect. That is going to work to some degree up to 4 clients per channel, but with more than that the chances of any client actually getting a connection start to be very slim. So how exactly do you arrive at 4 clients per channel? No answer? Pulling data from your ass? Get you head out of yours. Brownnosing oneself is a new one. Especially when 4-5 clients give the best combined throughput rate for TCP traffic for a 54 MBit connection?[1] You did pull them out of your ass, didn't you? Get you head out of it... I'm not brownnosing you. But I can't help but notice *I* have data and you pull numbers from your ass. In fact, 48 *active* clients on 3 channels have a combined throughput of 45 MBit/s of data (with all the TCP overhead and WLAN overheads and timeouts and retries and collisions already taken care off), so each PJ has 960 kbit/s.[1] A modem is 33.6 kbit/s. Do your math ... Learn how it works. Done. It works that way: 1. you claim something wrong 2. people provide real life observations, mathematical models, studies and more that say you're wrong 3. you claim they *all* don't know a thing and can't read. 4. You get plonked. Again. Instead there will virtually always be contention, and instead of being 4 times faster than a dialup, it would probably be about 10 times slower... at best! So 3 channels at 54 MBit/s can't keep up with 48 clients which sporadically try to pass data through them to the outside. Correct. Hmmm. [1] says something very different. You apparently didn't read what you are citing. s/You app/Floyd app/ s/you are/Wolfgang is/ Now it's correct. He http://serverfault.com/questions/192...le-wifi-router is someone connecting 60 iPads over 3 channels. We can find somebody somewhere who said almost anything on the Internet, but that doesn't make it correct. True --- after all, I found *you* saying wrong stuff. Regardless, just like the other URL, you don't seem to have actually read the article you cite! Please point out exactly where in the article it is said that more than 4 clients are a really huge problem for WiFi. Whom to believe? Those who have facts and others that have mathematical models congruent with yet other people's tests and experiences, or ... you ...? Tough question, innit? But then maybe you do get 48-PJ-news conferences pretty regular up in Barrow ... who knows? Yep, no answer. Floyd does not have *any* credentials. I see. Probably not, because you don't seem to know how it works or why and have no interest in learning eitehr. I'll await your "OK, I *was* completely wrong on all of my claims, including the WiFi and the learning!" admission. See, you haven't learned anything! I've learned you're an idiot, Floyd. You're wrong and too stupid to even see that you're wrong. Yes, my first calculations were wrong (way too naive and hence overestimating the effective netto bandwidth badly) but I learned. Fast. And now I'm quickly learning you are incapable of learning *and* wrong, hence not worth talking to. One more post will probably do it and you'll be back to the killfile. [1] http://paper.ijcsns.org/07_book/201207/20120704.pdf You *really* should read that paper and try to understand the significance of what it says! I did. Closely. It says that you're completely wrong in how common collisions are. The significance is that your claim | That is going to work to some degree up to 4 clients per | channel, but with more than that the chances of any client | actually getting a connection start to be very slim. is wrong. Trying to get a connection is the essentially the same as trying to sending data ... -Wolfgang [2] We're not having hidden nodes here. If we had, we could use RTS/CTS. |
#84
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Canon 6D
In article , Floyd L. Davidson
wrote: you didn't know what automatic meant and you think all base stations have vertically polarized antennas. I certainly don't know what *anything* means to *you*! it's what the industry defines it as, not me. *they* are the ones calling it automatic. stop trying to weasel out of it. I merely asked exactly what you meant, since *you* didn't have the sense to explain yourself. That is hardly trying to weasel out of anything. In fact we were talking about a client automatically changing channels to match the AP, and when you said the AP could be automatic is certainly made me think you were saying the AP adjusts to the client. That doesn't make sense, so I simply asked what you meant by "automatic". i'm not the one who first mentioned automatic. you got even that wrong. more importantly, many routers support automatic channel selection. it's not a new concept. how can you *not* know about it?? when's the last time you bought a router? Pretty reasonable... but you aren't. you claim to be the expert in everything so i assumed you knew what automatic was, especially since routers from many manufacturers these days (maybe even most) have it. again, it's not new. the natural conclusion was you were trying to play word games to avoid admitting you're wrong. And yes, virtually all base stations ahve vertically polarized antennas. previously, you said all, now it's virtually all? hilarious. Same thing. You probably don't know what the significance is anyway. i know full well what the significance is. knock off the insults and stay on topic. Of course many if not most units have always had antennas that can be adjusted. which means they can have any polarization anyone wants. if you think every user keeps them vertical, you're delusional. a lot of times i see one vertical and one horizontal. They *all* recommend using vertical polarization, no they definitely don't do that. you're wrong again. not only do they not recommend anything, but they don't even *mention* polarization anywhere in the user manuals! but there are good reasons to use horizontal in some special circumstances (mostly to restrict the range). that's a change from what you said the other day. so now there's a reason for horizontal? you're weaseling, again. by the way, horizontal polarization can *increase* range for some clients, such as smartphones, whose orientation is unknown and can change at any time. not that it matters. it's nowhere close to 'virtually all.' travel routers, for example, are polarized in whatever orientation they happen to be when used, particularly the battery operated ones, such as a cellular mifi device. And any instructions that mention antenna orientation will say to position the unit in a way the results in vertical orientation. wrong. you're out of touch with the real world and talking out your ass, again. there are no such instructions in any of the travel routers i have, 3 different ones, from 3 different manufacturers (apple, linksys & zoom). i checked two more user manuals for ones i don't have (verizon mifi & netcomm) and both of those didn't mention antenna orientation either. that's 5 out of 5 that don't say a single thing about it! furthermore, two of them (linksys & apple) have a built-in ac power plug so the orientation is dependent on the wall outlet. if the wall outlet is horizontal, so is the travel router. although many wall outlets are vertical, not all of them are, especially in hotels where such a router is likely to be used. the third travel router i have uses batteries and it can be in any orientation. it's thin and flat (roughly the size and shape of a deck of playing cards) and it's highly likely the polarization is *not* vertical when sitting on a table. Again, that is because vertical *is* the standard (for very good reasons), and will generally produce the best results. In the case of a direct line of sight with no multi-path there is about 30 dB loss from cross polarization. except that you cannot know the orientation of the client devices. vertical might have been preferred at one time but it's certainly not now. in the real world (not your world), smartphones, tablets and even laptops are used in many orientations, not just vertical. they can be horizontal, vertical and everything in between. many times the device is rotated during use. that's why some wifi base stations have *both* vertical and horizontal polarizations, or in some cases, at 45 degree offsets. other base stations may be one or the other, sometimes vertical and sometimes not. in the real world, polarization makes almost no difference to the user (as opposed to lab instruments). this is easily shown by rotating a smartphone or tablet and things keep working just as before. can a lab instrument measure a difference? probably, but if the user can continue to do whatever it was they were doing even though they rotated the device, then it does not matter what some lab instrument measures. to the user (which is what matters), it continues to work. again, real world situations. I haven't seen the insides of some of the smaller WIFI units for cameras and similar devices, but I would guess that at least some of them use circular polarization, just to avoid excessive loss from cross polarization. this is about routers, not cameras or other devices. travel routers are generally used relatively close to the client, so there's no need for anything fancy. Sigh. I drew a graphic and made a chart previously that showed *precisely* what the channel separation is. The simple fact is that yes it will increase interference if you choose anything else. it will not increase anything. Just interference. nope. Ignorance is bliss, and you seem blissful enough. then you must be incredibly happy. by the way, there are more sources of interference than just other wifi routers. |
#85
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Canon 6D
In article , Floyd L. Davidson
wrote: you can't control what neighbors do. sometimes picking something other than 1, 6 or 11 is the only option. It really is. Since everyone seems to allow their wifi station to pick the channel (based possibly on the traffic at that time and then no longer changing) I'm better off alone at 8 or 9. I get splashed to be sure, but not near as bad as if I stay on 1, 6 or 11. You get interference, if you choose Channel 8, from anyone that chooses any channel from 4 to 12. depends how far away they are. No, it depends on the signal strength relative to the desired signal. which depends how far away they are. Any given station can be farther away but also have a much stronger signal level. possible, but most routers have similar power and very few people have directional antennas, so distance is a good metric. If the signal strength for all other users total is equal to greater than 6 dB less than the RSL of the desired signal, you will have interference. That is, if there is one signal on Channel 8 and it is -6 dB or greater compared to your signal, you get interference. If there are two signals they can both be -9 dB below the desired signal, and you will get interference. If there are four signals the threshold is -12 dB, and so on. If you choose Channel 11 the only other choices that will affect you are those from 7 on up. All you have done by choosing Channel 8 is perhaps double the amount of interference. based on that, then 1 and 11 can be the only choices. Channels 1, 6 and 11 will not interfere with each other. nobody said they would. however, what *you* said is by picking 8, you get twice as much interference than 11, so based on that, picking 6 is even worse. It is true that picking 8 will get twice as much interference, and that is not true of 11. then 6 is the worst. choosing 6 means 2-10 can cause interference, which is almost the entire band. That is exactly the reason to assign 1, 6, and 11. in an ideal world, yes. No, in very practical world. That is the only way to get three clear channels operating at one time. If you choose Channel 8, it there can't be more than two channels operating without interference. however, you can't guarantee that everyone will adhere to that. nobody can. unfortunately, in the real world it doesn't work that way. Clearly it does. no, it definitely does not. you need to get out more. if they're too weak to be of significance, then it doesn't really matter what channel you or anyone else picks, does it? Not until someone close enough to actually have a greater signals strength cranks up their AP, and then you are toast if you picked the wrong channel! no need to crank up anything. Yes, if it is turned off then it won't interfere with you. But most people install these devices to actually use them. who said anything about turning them off??? in an apartment setting, a neighbor's base station could be as close as just a few feet away if it's near a shared wall, or a little more in the apartment directly overhead or below. what channels they pick *will* be an issue. Exactly. So choosing the most efficient channel assignment pattern is significant. yes it is, but the point is you can't enforce that, and there are other sources of interference than wifi base stations. sometimes people pick other channels. it's just how it is. in detached homes, the distances will obviously be greater so using the same channels will likely not be an issue, although in some cities houses are very close together so it could turn out to be a problem anyway. That is not necessarily true. These "shared wall" situations, and equally likely with overhead/below circumstances, often mean very lossy transmission paths. sometimes. it depends what's in the wall. when i stay in a hotel, i can see networks from other guests in other rooms. hotel wifi tends to suck, so they bring their own. It isn't generally just a matter of "distance". And often the distance traveled by the signal is not actually a direct line of sight anyway. Almost any wall causes significant loss at 2400MHz, and almost any metalic surface larger than an inch or so will reflect the signals too. Hence you may think, for example, that the signal you are picking up from the appartment above you is traveling 10 to 15 feet through the ceiling when in fact the path is in/out the (lossless) windows and bouncing off the foil backing on the insulation in the wall (or a metal sign attached to it) of the building across the street! that's a bit of a stretch. WIFI does strange things. not as strange as the arguments you make. You can weasel all you like, but technically there is only one right way: choose one of channel 1, 6 or 11. no weaseling at all. Won't be when you stop... in an ideal world, sure, use 1, 6 and 11. In a practical world, that is the right choice. but in the real world, people choose other channels. you see, in the real world, people pick channels *other* than those three. And my point is that it does *not* improve their service. that's *their* problem. the issue is what a given user needs to do to get the best service. it might be 1, 6 or 11, or it might not. i just did a survey and right *now* i see networks on 1, 2, 3, 6, 9 and 11. based on their strengths, picking 1, 6 or 11 is *not* the best choice for me. that's the real world. Let me say it again: use one of 1, 6 or 11 for best results. let me say it again, 1, 6 or 11 does *not* always give the best results. been there, done that. Use something else if results aren't what you want, but emotional yada yada is a good substitute. whatever that is supposed to mean. |
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