Performance Test: 802.11b Takes a Lickin' and Keeps on Tickin'
by Rob Flickenger03/29/2001
With all of the talk about the performance impacts of WEP (Wired Equivalent Privacy) and noisy environments, I thought I'd throw some quick, informal benchmarks together to see if any of this hearsay was true.
To test this, I generated a 1,441,792-byte file (as 1,441,792 bytes x 8 bits per byte = 11,534,336 bits, or 11 megabits) by copying it from /dev/urandom using dd.
I then tried sending this file to an IBSS (ad hoc, also known as peer to peer) node
like this:
$ time dd if=random.bits |ssh -c none 10.0.1.254 dd of=/dev/nullThis essentially means "Take these 11 million random bits, copy them over the network using no encryption, just dump them into the bit bucket on the other end, and tell me how long it took you." I did this to try to minimize the impact of disk usage and CPU crunching, and just try to make the bits fly as fast as possible.
I tried sending the file at 1, 2, 5.5, and 11 megabits per second, from a couple of different positions: about 25 feet away from the node (through three walls and a non-operational microwave oven), the same with the oven boiling some tea water, and then from about 20 feet away in the same room as the operating microwave oven. I did this with WEP encryption off, on, and at Lucent's 128-bit RC4, all without external antennas.
  Have you ever experienced microwave oven interference, or any other type for that matter, with your 802.11 network?
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The first interesting thing that I noticed was that, no matter how hard I tried, I couldn't squeeze out more than about 4 Mbits. This could be due to a number of factors, the most likely being that I'm using a cheap PCMCIA/ISA bus adapter in my router (a Pentium 233), and the bus probably just couldn't keep up. I'm really not so worried, as my Internet connection is only 1.544 Mbps max anyway! ;)
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Will microwave ovens blow your 802.11 network? Our tests say no, but your mileage may vary. |
Before we get to the numbers, I'd like to point out that even with the above fancy command, there was still a small amount of system overhead in actually getting the packets sent. As the exact amount is difficult to calculate but non-trivial, I decided to weigh the figures like this:
At 1 Mbps, it should take 11.00 seconds to transmit my 11 Mbit file, in the best possible case. On average (each test was sampled five times and averaged), it took 14.91 seconds to complete.
So, we have 3.91 seconds of unaccounted-for overhead (or 35 percent of the total transmission time.) For purposes of argument, we'll assume that the 1 Mbit speed is optimal, and deduct 35 percent from all transmission speeds (chalking it up to system overhead.) And so we are grading on a curve.
At any rate, here's the performance at 25 feet, through three walls and a solid wooden door, no antennas, behind the unplugged microwave, without WEP:
1 Mbps: 14.91 - 3.91 = 11.00 seconds = 1,048,576 bps (adjusted)
2 Mbps: 8.33 - 2.91 = 5.42 seconds = 2,128,106 bps
5.5 Mbps: 4.82 - 1.68 = 3.14 seconds = 3,673,355 bps
11 Mbps: 4.26 - 1.49 = 2.77 seconds = 4,164,020 bps
The same with 40-bit WEP:
1 Mbps: 15.09 - 5.28 = 9.81 seconds = 1,175,773 bps
2 Mbps: 8.36 - 2.92 = 5.44 seconds = 2,120,282 bps
5.5 Mbps: 4.89 - 1.71 = 3.18 seconds = 3,627,149 bps
11 Mbps: 4.60 - 1.61 = 2.99 seconds = 3,857,637 bps
And again with 128-bit RC4:
1 Mbps: 15.05 - 5.26 = 9.79 seconds = 1,178,175 bps
2 Mbps: 8.37 - 2.92 = 5.45 seconds = 2,116,391 bps
5.5 Mbps: 4.86 - 1.70 = 3.16 seconds = 3,650,106 bps
11 Mbps: 4.66 - 1.63 = 3.03 seconds = 3,806,711 bps
As you can see, WEP appears to have virtually no effect on throughput, until cranking 11 Mbps. The difference in transmission times was just about 1 percent. I believe it can be chalked up to natural variances (not to mention user error!) At 1 Mbps, WEP performance actually tested slightly better!
There was a bit of an impact at 11 Mbps (about 8 percent or so) when going to 128-bit encoding. Not sure what that means, as it wasn't even getting anywhere near 11 Mbps without WEP to begin with. Really, the highest figures should probably just be tossed until I figure out why it isn't transmitting efficiently.
As the difference in throughput was negligible, I left 128-bit encryption on for the remaining tests.
Next came the fun part. 300-watt microwave oven on at full blast, nuking a cup of water, while trying to upload an 11 Mbit file:
1 Mbps: 27.64 - 9.67 = 17.97 seconds = 641,866 bps
2 Mbps: 13.30 - 4.65 = 8.65 seconds = 1,333,449 bps
5.5 Mbps: 7.05 - 2.46 = 4.59 seconds = 2,512,927 bps
11 Mbps: 6.02 - 2.10 = 3.92 seconds = 2,942,432 bps
At 1 Mbps, I saw the worst performance when directly behind the running microwave oven, at a 45 percent performance hit. But at 11 Mbps, in the same setting, the performance was only down about 23 percent.
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Granted, that was a highly contrived test setting. I think the ambient room test (about 20 feet from the node, with a microwave oven chugging along in the same room) was more representative of what you can expect in the "real world":
1 Mbps: 16.86 - 5.90 = 10.96 seconds = 1,052,402 bps
2 Mbps: 9.15 - 3.20 = 5.95 seconds = 1,938,543 bps
5.5 Mbps: 8.52 - 2.98 = 5.54 seconds = 2,082,010 bps
11 Mbps: 5.07 - 1.77 = 3.30 seconds = 3,495,253 bps
There we have it: 11 percent loss at 1 Mbit; 8 percent loss at 11 Mbps.
So, in the absolute worst case, inches behind a running microwave and at 1 Mbps, you're still pulling 640 Kbps -- about double the speed of the average DSL line, and about 12 times the bandwidth of a "very fast" dial-up connection!
I can't wait to test the above against Bluetooth equipment running in the same environment -- assuming it ever makes it to market. ;)
Incidentally, the tea was delicious (although a bit too hot.) Mmmm ... Yerba Buena Maté.
Rob Flickenger is a long time supporter of FreeNetworks and DIY networking. Rob is the author of three O'Reilly books: Building Wireless Community Networks, Linux Server Hacks, and Wireless Hacks.
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Showing messages 1 through 29 of 29.
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802.11b Takes a Lickin' and Keeps on Tickin'
2004-09-13 04:13:28 HabiNet [Reply | View]
Not exactly scientific but you must have had some fun doing the tests. While I can't argue against your figures I would point out that in the real world your tests only go to show that while WEP encryption may offer a decrease in the absolute performance of a wireless network, in terms of throughput, the available speeds are still massively faster then your available ADSL circuit bandwidth. The effect on your system in the real world will be all but negligible if your simply using your router as an Internet gateway.
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Flawed Numbers
2003-09-22 05:43:15 anonymous2 [Reply | View]
Your numbers are very flawed for two reasons:
1: SSH has substantial overhead and slows you down
2: You're sending 11 million bits. Good. What about all of the packet headers? What about the link level headers? Those all counts as bits as well. Your throughput is likely about 9 to 10 mbps since the headers alone are going to be about 40 to 60 bytes long on EACH packet.
You wrote a book on this? That's pretty scary -
Flawed Numbers, etc.
2003-09-22 11:24:23 Rob Flickenger [Reply | View]
Please do keep in mind that I wrote this article about two and a half years ago. 802.11b was just hitting the scene, and I was running around a bit like an idiot trying to figure out what the tech was good for.
It has become common knowledge since then that a wireless card's listed rate is the speed at which it sends 802.11 traffic (sometimes referred to as the "radio rate"). There is significant overhead in the 802 protocols, accounting for more than half of the data sent. The best benchmarks I've seen for actual user data (including headers) on an 802.11b link is about 5Mbps. I haven't tried it myself, but I'm told that 802.11a and 802.11g, billed at "54Mbps", only push around 20Mbps of usable data. In my experience, running TCP/IP incurs about an additional 30% overhead or so.
At the time, I was more interested in the impact that a microwave oven had on 802.11b than in generating actual benchmarks. I thought that if I made my measurements the same way I could learn something from the difference.
There are, of course, much better tools for measuring the throughput of a link than ssh (ttcp for one).
But this experiment is flawed in more important ways. Probably my biggest mistake is in only attempting this on one channel, over only a couple of runs. It would be much more meaningful to have tried many runs on each channel, against a variety of devices.
Now, a couple of years later, it is readily apparent to me that ovens are the least of your worries on 2.4GHz (since even at their worst, they turn off after a couple of minutes). Panasonic 2.4GHz phones seem to be the worst of the lot in my experience. X-10 cameras are right up there, too.
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2.4 Ghz Panasonic Phone zaps WLAN signal strength
2003-08-02 19:48:50 anonymous2 [Reply | View]
I found this thread searching for a reason why my 2.4 GHz Panasonic phone would kill by wireless connection to my Dell Latitude x-200 laptop running XP. The pc-card and the base station are both Microsoft. I get an error showing I have "no signal strength" when using the phone near the laptop. The internet connection is broken and can be regained so far only by rebooting or by removing and re-inserting the wireless pc-card.
Curiously, the same pc-card in an older Dell Inspiron with W98 2ED with the same Microsoft base station never exhibited any problems.
- Lee from South Carolina
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absolutely
2003-05-12 19:23:27 anonymous2 [Reply | View]
when we use the microwave it doesn't work.....
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2.4GHz Cordless Phone Interference
2003-03-31 03:34:13 anonymous2 [Reply | View]
I used to have a Sony 2.4ghz Multihandset cordless phone. When one of the handsets was in use, it totally smashed my WLAN. No connection possible what so ever. I got rid of the phone for this reason.
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2.4 interference = 2.4 schmerence...blah blah blah
2002-12-30 22:55:31 anonymous2 [Reply | View]
I have a 2.4Ghz Home Security System. I have two 2.4Ghz Telephones (one upstairs, one downstairs). I have a 2.4Ghz Access Point in my house with a 10db antenna connected to it and I come into my house 2.4Ghz. You are all a bunch of tards...My system works flawlessly. In fact I had an Orinoco card in my laptop and sat at the neighbors house connected "back" to the Orinoco card in the AP (without an antenna) and still had a killer connection (half a block away). My neighbor connects onto my system sharing my link with no issues. The author of this article shot a successful 20 mile link. I do 1-20 mile links all day. YOU SHOULD LEARN HOW TO DO IT BEFORE YOU TRY TO SET SOMETHING UP. 802.11b thanx, you just made me a very wealthy man!!!
Spiderman
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Ok, What 802.11 channels did you use?
2002-11-22 14:00:44 anonymous2 [Reply | View]
The potential for interference is probably nil for Channel 1 BUT if you choose channel 10 your 802.11 would probably be toast. Microwave oven is near channel 10 dudes about 20 MHz wide, sloppy spectrum and is CW!!
This is also true of the phones. They have 4 or 5 channels. Instructions are usually to choose the quietest phone channel based on hearing it. Well, if used with 802.11 the channel with the most noise is nearest the 802.11.
802.11 is usually defaulted by the software guys to channel 1. This is away from the microwave but closer to the phones. At least the phones that I've seen.
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microwave oven interference
2002-10-11 09:04:57 anonymous2 [Reply | View]
I definitely take a hit to my Linksys wireless access point router while the microwave is running. It might be on same electrical circuit but it also sits on the other side of the wall from the oven...
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What about 2.4 GHz Cordless Phones?
2002-04-09 09:14:25 blwette [Reply | View]
Microwaves are relatively self-contained. What about the 2.4 GHz cordless phones? I've never actually tested it out, but if they are using the same ISM range as 802.11b, it seems possible that they could interfere. Are the phones using the same range?
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Bandwidth is measured in decimal
2001-07-06 06:02:44 tim_unsol [Reply | View]
When a communication protocol, such as 802.11, states that it supports x Mb/s, the "M" means million, or 1000000 and not mega, or 2^^20==1048576. Consequently, the calculations in this article are a bit off. e.g. the 11megabit file should take 1.048576 seconds in raw transmission time. Then there are the protocol overheads...
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Microwaves
2001-05-10 16:22:49 onkelbob [Reply | View]
As sustaining engineer working with RF since 83, no question a microwave oven (especially an old one) will disrupt ISM band communications. At one shop I worked, we manufactured and tested FHSS radios. We ceased testing at 11:30L every day because interference from the lunch room microwave ovens would disrupt and skew our tests.
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data point vs experiment
2001-04-03 12:16:45 vainst1k [Reply | View]
One wireless card, one wireless access point, one microwave oven oriented in one direction. That's one data point, not an experiment. (Not to mention absence of readings for humidity, temperature, and other basics.)
I'm embarrassed to be an O'Reilly reader when I see amateurish "articles" like this. Suggestion: "We don't have any decent new articles this week, so here's a Dilbert/Evil Geniuses cartoon to fill the space." -
data point vs experiment
2001-04-04 11:23:38 Rob Flickenger [Reply | View]
I'd just like to point out that my intent behind doing this piece was to debunk a couple of rumors that surround 802.11b equipment:
1) Using WEP kills througput
2) The stuff is useless in the presence of household microwave noise
To be sure, I could have tried different wattages of microwave ovens, added 2.4Ghz phones and even Bluetooth equipment, tried different manufacturer's radio equipment... But I'm not (nor do I try to present myself as) a one-man Consumer Reports.
What this informal experiment demonstrated (to me at least) was that in a typical household setting (my own house, in fact), the effects of background noise on 802.11b throughput is negligible.
Ten iterations per test, using the same equipment in the same position in as controlled a setting as one's kitchen can be, was enough to convince me of a trend.
By all means, don't take my word for it. Feel free to do your own benchmarks! As the caption on the photograph says, "your mileage may vary."
Regards,
--Rob
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flawed experiment
2001-03-30 17:22:04 cypherpunk [Reply | View]
'ssh -c none' is not overhead free by any stretch of the imagination.
'ssh -c none -m none' is closer, but still not what you wanted.
you want netcat.
as always, if ever in doubt - look at the source.
...
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It depends on whether you're inside the oven...
2001-03-30 16:54:09 human_bean [Reply | View]
The following offered, for your perusal:
As part of an emergency preparedness test, I was asked to roll out phones and networking inside a local Civic Center. A federal regulatory agency shows up with their 802.11 gear to show us yokels how things are done. Nothing worked. They couldn't get across the main ballroom (approx 500 feet), even using directional antenna The previous night, the center had been decorated for a dance event, and the decorations consisted of aluminiumised mylar fringes hanging from every wall and ceiling rafter, all fluttering in the breeze. The multipathing couldn't have been stronger if they tried.
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2.4 gig cordless phone interference?
2001-03-30 15:24:06 gbroiles [Reply | View]
Has anyone encountered interference between 802.11b equipment operating at 2.4 ghz and cordless 2.4 ghz phones? I have experienced interference first-hand between Panasonic and Vtech 2.4 ghz phones, and wouldn't be surprised if there's interference with other devices using the same parts of the spectrum. (Sure, I know that if they're using spread spectrum, they shouldn't interfere, but lots of things work much better in theory than in practice.) -
2.4 gig cordless phone interference? Of Course...
2001-03-30 17:09:34 human_bean [Reply | View]
Yes. There is plenty.
The problem is that the type of spread spectrum implemented in most wireless networking is not as robust as could be hoped. It is inexpensive, however.
Knowing how this stuff works, I'll wait for a while...
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what about 2.4ghz phones
2001-03-30 15:23:04 aminorex [Reply | View]
I find my 802.11 unusable in the presence of a
2.4ghz wireless phone.
900mhz phones are fine, though. -
what about 2.4ghz phones
2002-10-10 18:46:34 anonymous2 [Reply | View]
I just got an evaluation model 5.8ghz phone. So far, that range of spectrum is lonely. We'll be testing 802.11a stuff in its presence. -
what about 2.4ghz phones
2001-04-04 11:11:15 Rob Flickenger [Reply | View]
You mention an 802.11 card-- which one?
There are two different technologies used in the old 802.11 (non-b) cards: Frequency Hopping, and Direct Sequence Spread Spectrum.
Most 2.4Ghz phones use Frequency Hopping to try to cope with noise in the band. The problem is that other frequency hopping devices in the same band may get very near into phase with each other, causing noise most of the time! I suspect that your 802.11 card is a freqency hopper.
The later 802.11 cards (and all 802.11b equipment, like the Lucent gear in this article) use DSSS, which uses one of eleven possible 'channels' and does tricky math to work around errors. This stuff tends to do better in the presence of FHSS, but worse in the presence of other DSSS equipment on the same (or an overlapping) channel.
Incidentally, I didn't throw a 2.4G phone into the test environment for this article because I don't own one (donations gratefully accepted! =) Although I do have friends who use them happily right along side their home 802.11b networks.
--Rob
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what about 2.4ghz phones
2003-12-30 21:06:27 anonymous2 [Reply | View]
This is an interesting topic because I'm about ready to rip my phone out of the wall because I get so much static. I change the channel countless times and it's like a 1 in 10 chance of getting a clear channel... until I move. My wireless AP (Linksys BEFSR11) is an 802.11b on Channel 1, which is 2412 Mhz (2.412 GHz). My phone is a Panasonic 2.4 Ghz phone. What can I do to eliminate interference problems? I've looked at a spectrum of 802.11b channels and all of them are in the 2.4 GHz range, so I can't see a way of altering that at all!
ANy ideas are appreciated - alex(at)alexrox.net, if you will. -
what about 2.4ghz phones
2001-04-07 21:43:07 corey [Reply | View]
I thought it was supposed to be the other way around. I have heard that the 11Mb 802.11b DSSS handled the older 802.11 DSSS in the 2.4GHz space moderately well, but that FHSS at any speed would thrash DSSS and make it a very poor performer.
Would you please share more information?
Thanks,
-Corey -
what about 2.4ghz phones
2001-05-10 16:35:05 onkelbob [Reply | View]
It's true an FHSS transmitter that is in the path of your DSS receiver will induce many problems. FHSS signals are much stronger (over 20 dB) and will desensitize a DSS receiver therefore inducing errors. The solution is to identify the source (transmitter) and change your receive path to avoid "hearing" the transmitter. If the receiver is using omni-directional antena, change to a directional antenna. Another possibility is to change polarization (antenna orientation) of the DSS system (both TX and RX) or get the FHSS to chnge their polarization.
Home 2.4 Ghz cordless phones "should" work with home 802.11b systems because the phones will hear the interference from the AP and change over to another channel on the ISM band, i.e., you set the AP to operate on channel 1, the phone will usually hear that interference and move its center carrier over to channel 6 automatically.
Here endeth the lesson for today ;o)
Looking forward to your Bluetooth tests.
Here endeth the lesson for today ;o)