Re:A couple reasons to choose 802.11a over 802.11g
on
Faster, Stronger 802.11b
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· Score: 3, Informative
Wow. This post looks familiar. Oh yeah, because I originally posted it here. Only there, it had my name as the author of the post... A hint: Please include credit for the original content if you are going to repost a comment. Otherwise it is called plagarism.
A couple reasons to choose 802.11a over 802.11g
on
802.11b at 22mbps
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· Score: 5, Informative
First, the 2.4 GHz has a ton of other devices sharing the same spectrum, from Bluetooth to wireless headphones, to your microwave. 802.11a runs in the 5GHz band instead.
Second, according to the last proposals I'd heard of, 802.11g is going to achieve higher bandwidth by taking up more of the spectrum. In other words, it is going to use more channels to simultaneously broadcast data, rather than just being able to shove more data down the same channel. This means your own access points will begin to interfere with each other much sooner than your 802.11a or.11b APs will.
In general, it is going to depend on your situation as to which you wish to choose. 802.11g will be great for backwards compatibility, but the news coming out of IEEE seems to indicate that 54Mbps is more like something to shoot for than something they expect to achieve. 802.11a won't have compatibility, and it will also have a shorter range, but it will have higher speeds with less interference.
And in return, I'll pick a nit with your nits that you picked (try saying that three times fast...)
(Begin quote)
1. I understand that a lot had to be cut for time, and to add some hollywood moments here and there, but why remove the repair of Aragorne's sword? It would seem to be critical later on.
(end quote)
There is a very good reason it was cut out: It actually wasn't. At least, not yet. The shattered sword, is not repaired until The Return of the King. The sword you see Aragorn weilding is just a normal sword that he has for defense (as I recall, he had a normal sword in the books, too). I doubt that the reforging of Aragorn's sword will be cut when we get to see the third movie.
There were just too many threads I wanted to reply to, so I figured I'd just put everything I had to say in one post, so here goes:
1. The statement that Bluetooth is lower power than 802.11 is currently false. Okay, it has a lower power transmitter, yes, but so far, last I knew, nobody had produced a Bluetooth radio that wasn't at least as much of a power hog as an 802.11 radio... and any 802.11 radio that has a power-saving mode does _much_ better than a Bluetooth radio. Bluetooth was also supposed to be cheaper, but the manufacturers are discovering that they are having a tough time bringing down the cost on that, too. Given time, these problems can be overcome, however, 802.11 happens to have a large headstart on both the cost and power fronts, and therefore has a good chance of preventing Bluetooth from being able to compete (nobody wants to invest a bunch of resources into a standard that the market hasn't yet truly clamored for).
2. Bluetooth and 802.11b interoperability. Without breaking one standard or the other, it ain't going to happen. And even if you do break one standard, it won't be backwards compatible. The two standards conflict too much. 802.11b has a back-off mechanism. Bluetooth doesn't. I actually did some work looking into building a Bluetooth/802.11b AP that would try to cleanly give both Bluetooth and 802.11b time on the air without breaking either standard. It's too difficult. Bluetooth is just to strict on the timing (not to mention the big problem that some Bluetooth cards refuse to give up being the Master).
3. 802.11 security was not broken. WEP was broken. Badly. But WEP is not the end-all, be-all of security. And yes, the industry _is_ working on better security, and has been for some time. IEEE 802.11 Task Group e is still in the process of agreeing upon a method for point-to-point security, with dynamically session keys, including a username/password setup. This is what the industry has wanted for some time. WEP was only meant to slow down the script kiddies who would just sit in parking lots with their cards set to associate to "ANY". I really wish people would stop assuming that WEP is the entirety of wireless security. It is not, and was never intended to be. One more note on this: it was not 802.11x that was broken. I'm not sure what 802.11x is, but it isn't a security standard. 802.1x is a LAN security standard, but even that isn't what was broken. Just WEP.
4. 802.11, 802.11a, 802.11b, 802.11. 802.11 is the general IEEE group for Wireless LAN networking. 802.11b is the 11Mbps standard. 802.11a is the 5GHz 54Mbps standard (once they decide exactly what that standard is). TGe, which should translate to 802.11e will be the new security standard. There are others (including a standard for 22Mbps in the 2.4GHz band, which I _think_ is 802.11h), but I don't remember what most of them are.
5. Wi-Fi stands for "Wireless Fidelity". Basically, a bunch of 802.11 card manufacturers got tired of the fact that different cards that implemented IEEE 802.11 were not interoperable. So WECA was born (Wireless Ethernet Compatibility Alliance). WECA decided that "IEEE 802.11" wasn't a marketing-friendly name, so they came up with "Wireless Fidelity" or "Wi-Fi" for short. Despite the marketing speak, this is actually a good organization. They have a whole slew of tests to determine whether an 802.11 radio is compatible with others that have passed the tests. If they pass, they get to put the Wi-Fi logo on their product. If a product has the Wi-Fi logo, then it can interoperate with any other radio that has passed the WECA tests. So there is a very minor distinction between Wi-Fi and 802.11. Basically, it is possible for a radio to implement 802.11 and not be Wi-Fi, but at this point, no company in their right mind would do so.
Well, that pretty much ends my rant. Take it for what you will.
> i'm not very well versed in encryption schemes,
> but why is it that the encryption schemes in > DeCSS, Adobe PDF, and now 802.11 are so 'easily'
> broken, as opposed to 3DES or RSA that are
> being used in SSH & SSL? why aren't these
> algorithms being applied in 802.11?
A very simple reason underlies all of this: cost.
You see, your PC has a whole lot more horsepower than a PC card, both in terms of CPU and in terms of memory. It can easily afford the memory space and CPU cycles to perform beefier algorithms. PC cards, on the other hand, are much more limited, due to the fact that in order to make any profit, they have to be made for as little money as possible (believe it or not, pretty much all 802.11 radios are sold with exceedingly low profit margins. You'll notice the cheaper ones have lesser or no WEP capabilities, for instance). A few things sacrificed to cost: CPU speed, FLASH space, and RAM size. This is an environment where 80MHz is a high-powered CPU, and 1MB is alot of storage capacity/memory space. WEP encryption is only one of many, many other options that have to fit in there. Now, one option is to put the encryption into its own hardware. That frees up CPU cycles, plus some RAM space and FLASH (though not all by a long shot). However, hardware encryption adds to the cost of the PC card. In other words, it's real hard to win in these situations. This is why all manufacturers of WiFi radios recommend using VPN over a wireless connection, and not relying on WEP. WEP is there to help (it'll at least stop the random script kiddie from setting their card to associate to "ANY", walking through your parking lot and hopping on your LAN), but it was never meant to be the end-all-be-all of security for wireless connections.
That being said, IEEE is working on further security standards that require a lot more pieces (e.g. authentication servers, etc), but those standards are not yet finalized, and even when they are, the radios, access points, and servers will all cost extra.
It all boils down to this: to get a more adequate security system implemented costs more money, and most people don't want to spend more money on 802.11 equipment. (At least, that's been my personal observation, based on conversations with friends and customers of 802.11 equipment).
> compared to Mark Tilden's robots. He's been > building light-seeking robots for years, and
> he's working on robots that are going to work
> on the Moon.
Except that the CMU robot does more than just crawl around chasing the sun. Hyperion doesn't just follow the sun. It makes sure it keeps the sun in sight, while also making intelligent decisions about how to avoid obstacles. All this while also providing video transmission, and collecting scientific data. This requires a lot more power and a more sophisticated AI than Tilden's creations, which just follow light sources (and have no AI at all, for that matter). Tilden's projects are more meant to follow a pattern of evolution: give the robots some capabilities, and see how it turns out. Hyperion, on the other hand, is built for a specific purpose, which requires more capabilities right away, and which need to be controlled in a known manner.
This is not meant to be a knock at Tilden. His research is interesting, and may well lead to new avenues of robotic development in the future. His robots, however, are not suitable for the mission that Hyperion can fulfill, simply due to the fact that they do not have all of the capabilities that Hyperion does.
As an engineer who works on 802.11 radios, I have a few issues with these tests.
First, the author performed only one test for each configuration. You can never come to a valid conclusion about performance from a one-shot test.
Second, the author doesn't really know much about RF, otherwise they'd realize that Microwaves are shielded to prevent from cooking the person operating the thing. While the shielding doesn't stop everything, it stops enough to let most 802.11 traffic get through without too much difficulty. As others have pointed out, the way to go is to operate other devices that communicate at 2.4GHz, such as certain cordless phones, Bluetooth devices, etc.
Third, the author doesn't appear to have read much on 802.11, or the author would realize that some amount of the overhead involved in 802.11 is used up in wireless headers that a simple application is never going to know exist.
Fourth, the author used tests on one vendor's radio to come to a conclusion about all 802.11 radios, and I can tell you that not all radios are created equally.
On the other hand, the author's results aren't actually terribly off from the performance seen in most 802.11b radios. Most 802.11b radios actually get a final throughput of about 3-5Mbps when running at "11 Mbps." Some of this is due to bus speed limitations (PCMCIA is slow), and some of it is due to the radios themselves (hey, you try getting a nice fast processor in there and maintain the price points), but whatever the limitation, no radio gets much more than 5Mbps in the best-case scenario (at least, of the radios currently on the market).
In the meantime, I'm looking forward to 802.11a, which will operate in the 5GHz band (hopefully, there will be less interference there) and should have a throughput of about 54Mbps (if they can ever finalize a standard, that is).
Well, most digital cordless phones seem to be either 900MHz or 2.4GHz. 802.11 runs at 2.4-2.4835MHz in the US, and bluetooth runs at 2.4GHz as well. Both the phones and, AFAIK the wireless data technologies, use frequency hopping so they should be able to coexist peacefully.
Actually, almost all of the 802.11b (definitely anything with a WiFi logo) uses Direct Sequence, rather than Frequency Hopping. Another thing to note is that _anything_ operating in the 2.4GHz band has the potential to interfere. I've seen a Frequency Hopping radio punch holes through a Direct Sequence radios throughput, because it's hopping happened to correspond to the same frequency at times (the frequency hopper also had a 100mW transmitter compared to a 35mW transmitter on the Direct Sequence radio).
Actually, the Ethernet Client Bridge (one of the two wireless products announced yesterday) does come with configuration software for linux, and does not need drivers at all.
ObDisclaimers: I work for 3Com, but I am currently speaking as my own person, and not as a representative of the company I work for.
That aside, yes, we still make lots of things. We still make lots of NICs (last I knew, every Dell computer ships with a 3Com chip on board). We do still make switches, plus we're expanding to gigabit ethernet over copper. My personal favorite, (since it happens to be what I work on) is the wireless networking that we do (IEEE 802.11b). In fact, for wireless, we just announced two new products just yesterday.
Usually, even in accademia knowing who to ask and what to ask are just as (if not more) important than being able to do it yourself.
Asking questions is quite a bit different from copying code. Copying code without understanding it does not teach the student anything. It is possible that a student understands the code they copied, but how do you prove that? Besides, experience in writing your own solution to a problem is very useful. In some cases, it is useful just because it shows you the wrong way to do something.
Allow me to re-phrase my statement. Projects teach students to develop their problem-solving skills. I had not intended my statement to mean that the projects teach them how to solve specific problems, but rather how to work on problems in general. Instruction teaches the theory behind the implementation, while the project gives the student a chance to figure out how to implement that theory. Both aspects are important in teaching people how to be engineers.
In the real world, re-use is excellent, because it is efficient, saves time, and saves costs. In academia, specifically, when it is a class project, the purpose is to teach the students how to do things, rather than just grab someone else's code. The focus is not on saving time and money, but on learning how to do things themselves. After all, if the student only learns to grab somebody else's code, and not write their own version, they can face a couple of problems:
1) If they encounter a situation where they can't re-use code, and they never learned how to write it, now what do they do? Granted, this is an extreme example, but it can and does happen.
2) If the code they re-use has undocumented bugs in it, or was originally meant for a different purpose, blindly re-using the code can do more harm than good. This is an extremely likely situation (especially with student code!).
Remember, the purpose of assignments is to teach how to solve problems by example. By giving the student direct experience in how to solve the problem, the student learns more than just what's in the book or someone else's comments.
Classes are not meant to duplicate the real world. If they were, there would not be any purpose to them; we would all just need to go straight into the real world. Classes are supposed to be used to teach students how to solve problems. That means getting them to do it themselves, and not having someone do it for them. Using someone else's code, even if only for a portion of the code, is having someone else do it for them. Thus, it is considered cheating.
At least, when I was a TA, that is how I would have considered it.
Working at a robotics company, I can tell you exactly why Linux runs on so many RoboCup (and AAAI) robots: It's free. You see, the vast majority of the customers of robots are academic universities, all of whom want a discount, because they're running on a tight budget. The hardware on robots (especially mobile robots) can get real exepnsive, real quick. If the job can be done with a free OS, it will be.
Don't get me wrong, Linux is my favorite OS, and I think it's great that it is used on robots, but it isn't like it is used simply because it is inherently better for the job. It is used because it does the job for the right price.
I was trying to refute the original statement that using electric power "is only burning carbon elsewhere." Yes, other sources have their impact, but some impact is less than others.
> But how do you crack water? With electricity! The economies simply aren't there.
One also needs electricity and fuel to get oil out of the ground. How come the economy exists to do one and not the other?
> Electricity simply redistributes where the carbon is burned Unless, of course, the electricity is provided by solar power, wind power, geothermal power, or a hydroelectric dam. As technology finds cleaner, more efficient methods of generating electricity (and the country actually implements them), electric cars would be able to continue running without change, which is an advantage over, for instance, natural gas, which is also a fossil fuel
> Hydrogen is very unstable (and can't be found in a mine like Petroleum). A) Hydrogen isn't as unstable as you seem to think it is. B) Even if you could mine for hydrogen, why go to all that effort? In case you forgot, water is easily cracked into hydrogen and oxygen, and that is far from the only source of hydrogen around. Hydrogen is fairly plentiful, certainly more so than petroleum.
Actually, that's not entirely accurate. Most bands hope to get their major record deal through word of mouth, and constantly play nightclubs and such trying to do so. The people who actually get signed, however, send demo tapes to various record labels, hoping that one of them will sign them on. Don't get me wrong, occasionally groups do get signed thanks to word of mouth, but my impression is that the majority don't.
At least, this has been the impression I've gotten from various musician interviews.
I am not sure if other companies implement this, but I do know that the WaveLAN Access point can be configured to deby unencrypted data. In this case, even if they try to associate, it will do them no good, since the Access Point will drop the packets they send.
Additional note, I forgot to mention Access Point configurability... The biggest drawback to Lucent's Access Point is that at the current time, it can only be configured via their (Windows) WaveMANAGER program. Both Proxim's and Aironet's Access Points can be configured via telnet or a web interface, and thus are configurable via Linux.
Proxim: One of the engineers at Proxim maintains a mailing list for running RangeLAN2 and symphony radios under linux. It gets a fair amount of traffic, and updates are posted fairly often. You can download the driver at: Lucent: http://www.komacke.com/distribution.html
My personal opinion is that the Aironet driver is kind of nice, since it is small and efficient (neither the Lucent nor the Proxim drivers are), and since Aironet has an 11Mb radio, is compatible at least with Lucent's Access Points (and should be with other 802.11 radios), Aironet is nice if you want speed under linux. Unfortunately, I am not sure whether Aironet supports WEP (Wired Equivalent Privacy) or not yet, and I know the Linux driver doesn't yet, so if you are interested in Security, I would recommend the Lucent Radio.
Obligatory Note: This is my personal opinion, and should not be construed as the opinion of any other entity.
Wireless networking done by Proxim's RangeLAN2, Symbols Spectrum24, Lucent's WaveLAN, and Aironet's 802.11 radios all communicate over the radio waves at the MAC layer of networking (I pick these radios specifically, because these are the ones I currently work with). Thus, if you are using SSH, that should be more or less as secure as if you aren't, since either way, the data is encrypted. The real question should be about how secure wireless connections are when you are running, say, standard telnet, or web browsing without SSL, and such. In those cases, there is the possibility that someone can associate to your network from outside the building with a wireless card, and sniff your packets. There is something you can do about this. The IEEE 802.11 wireless standard also provides for WEP (Wired Equivalent Privacy) encryption. The idea is that wired communication should be at least as safe as wired communication. This encrypts data when it is sent over a radio, and decrypts it on the receiving radio. Out of the radios I've worked with, I know for certain that Lucent's WaveLAN implements WEP with both 64 and 128 bits keys (depending on which version of the card you buy). Aironet is supposed to support WEP as well, but last I knew, they hadn't yet (this may have changed). Proxim's RangeLAN2 doesn't follow the 802.11 standard, however they do have their own security built-in with a radio security ID, though I do not recall how strong this security is.
Slashdot Mirror
Wow. This post looks familiar.
Oh yeah, because I originally posted it here.
Only there, it had my name as the author of the post...
A hint: Please include credit for the original content if you are going to repost a comment. Otherwise it is called plagarism.
First, the 2.4 GHz has a ton of other devices sharing the same spectrum, from Bluetooth to wireless headphones, to your microwave. 802.11a runs in the 5GHz band instead.
.11b APs will.
Second, according to the last proposals I'd heard of, 802.11g is going to achieve higher bandwidth by taking up more of the spectrum. In other words, it is going to use more channels to simultaneously broadcast data, rather than just being able to shove more data down the same channel. This means your own access points will begin to interfere with each other much sooner than your 802.11a or
In general, it is going to depend on your situation as to which you wish to choose. 802.11g will be great for backwards compatibility, but the news coming out of IEEE seems to indicate that 54Mbps is more like something to shoot for than something they expect to achieve. 802.11a won't have compatibility, and it will also have a shorter range, but it will have higher speeds with less interference.
And in return, I'll pick a nit with your nits that you picked (try saying that three times fast...)
(Begin quote)
1. I understand that a lot had to be cut for time, and to add some hollywood moments here and there, but why remove the repair of Aragorne's sword? It would seem to be critical later on.
(end quote)
There is a very good reason it was cut out: It actually wasn't. At least, not yet. The shattered sword, is not repaired until The Return of the King. The sword you see Aragorn weilding is just a normal sword that he has for defense (as I recall, he had a normal sword in the books, too). I doubt that the reforging of Aragorn's sword will be cut when we get to see the third movie.
There were just too many threads I wanted to reply to, so I figured I'd just put everything I had to say in one post, so here goes:
1. The statement that Bluetooth is lower power than 802.11 is currently false. Okay, it has a lower power transmitter, yes, but so far, last I knew, nobody had produced a Bluetooth radio that wasn't at least as much of a power hog as an 802.11 radio... and any 802.11 radio that has a power-saving mode does _much_ better than a Bluetooth radio. Bluetooth was also supposed to be cheaper, but the manufacturers are discovering that they are having a tough time bringing down the cost on that, too. Given time, these problems can be overcome, however, 802.11 happens to have a large headstart on both the cost and power fronts, and therefore has a good chance of preventing Bluetooth from being able to compete (nobody wants to invest a bunch of resources into a standard that the market hasn't yet truly clamored for).
2. Bluetooth and 802.11b interoperability. Without breaking one standard or the other, it ain't going to happen. And even if you do break one standard, it won't be backwards compatible. The two standards conflict too much. 802.11b has a back-off mechanism. Bluetooth doesn't. I actually did some work looking into building a Bluetooth/802.11b AP that would try to cleanly give both Bluetooth and 802.11b time on the air without breaking either standard. It's too difficult. Bluetooth is just to strict on the timing (not to mention the big problem that some Bluetooth cards refuse to give up being the Master).
3. 802.11 security was not broken. WEP was broken. Badly. But WEP is not the end-all, be-all of security. And yes, the industry _is_ working on better security, and has been for some time. IEEE 802.11 Task Group e is still in the process of agreeing upon a method for point-to-point security, with dynamically session keys, including a username/password setup. This is what the industry has wanted for some time. WEP was only meant to slow down the script kiddies who would just sit in parking lots with their cards set to associate to "ANY". I really wish people would stop assuming that WEP is the entirety of wireless security. It is not, and was never intended to be. One more note on this: it was not 802.11x that was broken. I'm not sure what 802.11x is, but it isn't a security standard. 802.1x is a LAN security standard, but even that isn't what was broken. Just WEP.
4. 802.11, 802.11a, 802.11b, 802.11. 802.11 is the general IEEE group for Wireless LAN networking. 802.11b is the 11Mbps standard. 802.11a is the 5GHz 54Mbps standard (once they decide exactly what that standard is). TGe, which should translate to 802.11e will be the new security standard. There are others (including a standard for 22Mbps in the 2.4GHz band, which I _think_ is 802.11h), but I don't remember what most of them are.
5. Wi-Fi stands for "Wireless Fidelity". Basically, a bunch of 802.11 card manufacturers got tired of the fact that different cards that implemented IEEE 802.11 were not interoperable. So WECA was born (Wireless Ethernet Compatibility Alliance). WECA decided that "IEEE 802.11" wasn't a marketing-friendly name, so they came up with "Wireless Fidelity" or "Wi-Fi" for short. Despite the marketing speak, this is actually a good organization. They have a whole slew of tests to determine whether an 802.11 radio is compatible with others that have passed the tests. If they pass, they get to put the Wi-Fi logo on their product. If a product has the Wi-Fi logo, then it can interoperate with any other radio that has passed the WECA tests. So there is a very minor distinction between Wi-Fi and 802.11. Basically, it is possible for a radio to implement 802.11 and not be Wi-Fi, but at this point, no company in their right mind would do so.
Well, that pretty much ends my rant. Take it for what you will.
-Freeptop
> i'm not very well versed in encryption schemes,
> but why is it that the encryption schemes in
> DeCSS, Adobe PDF, and now 802.11 are so 'easily'
> broken, as opposed to 3DES or RSA that are
> being used in SSH & SSL? why aren't these
> algorithms being applied in 802.11?
A very simple reason underlies all of this: cost.
You see, your PC has a whole lot more horsepower than a PC card, both in terms of CPU and in terms of memory. It can easily afford the memory space and CPU cycles to perform beefier algorithms. PC cards, on the other hand, are much more limited, due to the fact that in order to make any profit, they have to be made for as little money as possible (believe it or not, pretty much all 802.11 radios are sold with exceedingly low profit margins. You'll notice the cheaper ones have lesser or no WEP capabilities, for instance). A few things sacrificed to cost: CPU speed, FLASH space, and RAM size. This is an environment where 80MHz is a high-powered CPU, and 1MB is alot of storage capacity/memory space. WEP encryption is only one of many, many other options that have to fit in there. Now, one option is to put the encryption into its own hardware. That frees up CPU cycles, plus some RAM space and FLASH (though not all by a long shot). However, hardware encryption adds to the cost of the PC card. In other words, it's real hard to win in these situations. This is why all manufacturers of WiFi radios recommend using VPN over a wireless connection, and not relying on WEP. WEP is there to help (it'll at least stop the random script kiddie from setting their card to associate to "ANY", walking through your parking lot and hopping on your LAN), but it was never meant to be the end-all-be-all of security for wireless connections.
That being said, IEEE is working on further security standards that require a lot more pieces (e.g. authentication servers, etc), but those standards are not yet finalized, and even when they are, the radios, access points, and servers will all cost extra.
It all boils down to this: to get a more adequate security system implemented costs more money, and most people don't want to spend more money on 802.11 equipment. (At least, that's been my personal observation, based on conversations with friends and customers of 802.11 equipment).
-Freeptop
> compared to Mark Tilden's robots. He's been
> building light-seeking robots for years, and
> he's working on robots that are going to work
> on the Moon.
Except that the CMU robot does more than just crawl around chasing the sun. Hyperion doesn't just follow the sun. It makes sure it keeps the sun in sight, while also making intelligent decisions about how to avoid obstacles. All this while also providing video transmission, and collecting scientific data. This requires a lot more power and a more sophisticated AI than Tilden's creations, which just follow light sources (and have no AI at all, for that matter). Tilden's projects are more meant to follow a pattern of evolution: give the robots some capabilities, and see how it turns out. Hyperion, on the other hand, is built for a specific purpose, which requires more capabilities right away, and which need to be controlled in a known manner.
This is not meant to be a knock at Tilden. His research is interesting, and may well lead to new avenues of robotic development in the future. His robots, however, are not suitable for the mission that Hyperion can fulfill, simply due to the fact that they do not have all of the capabilities that Hyperion does.
As an engineer who works on 802.11 radios, I have a few issues with these tests.
First, the author performed only one test for each configuration. You can never come to a valid conclusion about performance from a one-shot test.
Second, the author doesn't really know much about RF, otherwise they'd realize that Microwaves are shielded to prevent from cooking the person operating the thing. While the shielding doesn't stop everything, it stops enough to let most 802.11 traffic get through without too much difficulty. As others have pointed out, the way to go is to operate other devices that communicate at 2.4GHz, such as certain cordless phones, Bluetooth devices, etc.
Third, the author doesn't appear to have read much on 802.11, or the author would realize that some amount of the overhead involved in 802.11 is used up in wireless headers that a simple application is never going to know exist.
Fourth, the author used tests on one vendor's radio to come to a conclusion about all 802.11 radios, and I can tell you that not all radios are created equally.
On the other hand, the author's results aren't actually terribly off from the performance seen in most 802.11b radios. Most 802.11b radios actually get a final throughput of about 3-5Mbps when running at "11 Mbps." Some of this is due to bus speed limitations (PCMCIA is slow), and some of it is due to the radios themselves (hey, you try getting a nice fast processor in there and maintain the price points), but whatever the limitation, no radio gets much more than 5Mbps in the best-case scenario (at least, of the radios currently on the market).
In the meantime, I'm looking forward to 802.11a, which will operate in the 5GHz band (hopefully, there will be less interference there) and should have a throughput of about 54Mbps (if they can ever finalize a standard, that is).
Well, most digital cordless phones seem to be either 900MHz or 2.4GHz. 802.11 runs at 2.4-2.4835MHz in the US, and bluetooth runs at 2.4GHz as well. Both the phones and, AFAIK the wireless data technologies, use frequency hopping so they should be able to coexist peacefully.
Actually, almost all of the 802.11b (definitely anything with a WiFi logo) uses Direct Sequence, rather than Frequency Hopping. Another thing to note is that _anything_ operating in the 2.4GHz band has the potential to interfere. I've seen a Frequency Hopping radio punch holes through a Direct Sequence radios throughput, because it's hopping happened to correspond to the same frequency at times (the frequency hopper also had a 100mW transmitter compared to a 35mW transmitter on the Direct Sequence radio).
Actually, the Ethernet Client Bridge (one of the two wireless products announced yesterday) does come with configuration software for linux, and does not need drivers at all.
ObDisclaimers: I work for 3Com, but I am currently speaking as my own person, and not as a representative of the company I work for.
That aside, yes, we still make lots of things. We still make lots of NICs (last I knew, every Dell computer ships with a 3Com chip on board). We do still make switches, plus we're expanding to gigabit ethernet over copper. My personal favorite, (since it happens to be what I work on) is the wireless networking that we do (IEEE 802.11b). In fact, for wireless, we just announced two new products just yesterday.
Usually, even in accademia knowing who to ask and what to ask are just as (if not more) important than being able to do it yourself.
Asking questions is quite a bit different from copying code. Copying code without understanding it does not teach the student anything. It is possible that a student understands the code they copied, but how do you prove that? Besides, experience in writing your own solution to a problem is very useful. In some cases, it is useful just because it shows you the wrong way to do something.
Allow me to re-phrase my statement. Projects teach students to develop their problem-solving skills. I had not intended my statement to mean that the projects teach them how to solve specific problems, but rather how to work on problems in general. Instruction teaches the theory behind the implementation, while the project gives the student a chance to figure out how to implement that theory. Both aspects are important in teaching people how to be engineers.
In the real world, re-use is excellent, because it is efficient, saves time, and saves costs. In academia, specifically, when it is a class project, the purpose is to teach the students how to do things, rather than just grab someone else's code. The focus is not on saving time and money, but on learning how to do things themselves. After all, if the student only learns to grab somebody else's code, and not write their own version, they can face a couple of problems:
1) If they encounter a situation where they can't re-use code, and they never learned how to write it, now what do they do? Granted, this is an extreme example, but it can and does happen.
2) If the code they re-use has undocumented bugs in it, or was originally meant for a different purpose, blindly re-using the code can do more harm than good. This is an extremely likely situation (especially with student code!).
Remember, the purpose of assignments is to teach how to solve problems by example. By giving the student direct experience in how to solve the problem, the student learns more than just what's in the book or someone else's comments.
Classes are not meant to duplicate the real world. If they were, there would not be any purpose to them; we would all just need to go straight into the real world. Classes are supposed to be used to teach students how to solve problems. That means getting them to do it themselves, and not having someone do it for them. Using someone else's code, even if only for a portion of the code, is having someone else do it for them. Thus, it is considered cheating.
At least, when I was a TA, that is how I would have considered it.
Working at a robotics company, I can tell you exactly why Linux runs on so many RoboCup (and AAAI) robots: It's free. You see, the vast majority of the customers of robots are academic universities, all of whom want a discount, because they're running on a tight budget. The hardware on robots (especially mobile robots) can get real exepnsive, real quick. If the job can be done with a free OS, it will be.
Don't get me wrong, Linux is my favorite OS, and I think it's great that it is used on robots, but it isn't like it is used simply because it is inherently better for the job. It is used because it does the job for the right price.
I was trying to refute the original statement that using electric power "is only burning carbon elsewhere." Yes, other sources have their impact, but some impact is less than others.
> But how do you crack water? With electricity! The economies simply aren't there.
One also needs electricity and fuel to get oil out of the ground. How come the economy exists to do one and not the other?
> Electricity simply redistributes where the carbon is burned
Unless, of course, the electricity is provided by solar power, wind power, geothermal power, or a hydroelectric dam. As technology finds cleaner, more efficient methods of generating electricity (and the country actually implements them), electric cars would be able to continue running without change, which is an advantage over, for instance, natural gas, which is also a fossil fuel
> Hydrogen is very unstable (and can't be found in a mine like Petroleum).
A) Hydrogen isn't as unstable as you seem to think it is.
B) Even if you could mine for hydrogen, why go to all that effort? In case you forgot, water is easily cracked into hydrogen and oxygen, and that is far from the only source of hydrogen around. Hydrogen is fairly plentiful, certainly more so than petroleum.
Actually, that's not entirely accurate. Most bands hope to get their major record deal through word of mouth, and constantly play nightclubs and such trying to do so. The people who actually get signed, however, send demo tapes to various record labels, hoping that one of them will sign them on.
Don't get me wrong, occasionally groups do get signed thanks to word of mouth, but my impression is that the majority don't.
At least, this has been the impression I've gotten from various musician interviews.
I am not sure if other companies implement this, but I do know that the WaveLAN Access point can be configured to deby unencrypted data. In this case, even if they try to associate, it will do them no good, since the Access Point will drop the packets they send.
Additional note, I forgot to mention Access Point configurability...
The biggest drawback to Lucent's Access Point is that at the current time, it can only be configured via their (Windows) WaveMANAGER program. Both Proxim's and Aironet's Access Points can be configured via telnet or a web interface, and thus are configurable via Linux.
Proxim:
One of the engineers at Proxim maintains a mailing list for running RangeLAN2 and symphony radios under linux. It gets a fair amount of traffic, and updates are posted fairly often.
You can download the driver at:
Lucent:
http://www.komacke.com/distribution.html
There is a stripped down version of Lucent's WaveLAN driver code which is used by the WaveLAN driver for Linux. You can find this one at:
http://www.wavelan.com/support/s oftware/index.html
There is also a Linux driver for the Aironet radios which can be found at: ftp://sourceforge.org/pcmcia/contrib/
My personal opinion is that the Aironet driver is kind of nice, since it is small and efficient (neither the Lucent nor the Proxim drivers are), and since Aironet has an 11Mb radio, is compatible at least with Lucent's Access Points (and should be with other 802.11 radios), Aironet is nice if you want speed under linux. Unfortunately, I am not sure whether Aironet supports WEP (Wired Equivalent Privacy) or not yet, and I know the Linux driver doesn't yet, so if you are interested in Security, I would recommend the Lucent Radio.
Obligatory Note: This is my personal opinion, and should not be construed as the opinion of any other entity.
Wireless networking done by Proxim's RangeLAN2, Symbols Spectrum24, Lucent's WaveLAN, and Aironet's 802.11 radios all communicate over the radio waves at the MAC layer of networking (I pick these radios specifically, because these are the ones I currently work with). Thus, if you are using SSH, that should be more or less as secure as if you aren't, since either way, the data is encrypted.
The real question should be about how secure wireless connections are when you are running, say, standard telnet, or web browsing without SSL, and such. In those cases, there is the possibility that someone can associate to your network from outside the building with a wireless card, and sniff your packets.
There is something you can do about this. The IEEE 802.11 wireless standard also provides for WEP (Wired Equivalent Privacy) encryption. The idea is that wired communication should be at least as safe as wired communication. This encrypts data when it is sent over a radio, and decrypts it on the receiving radio.
Out of the radios I've worked with, I know for certain that Lucent's WaveLAN implements WEP with both 64 and 128 bits keys (depending on which version of the card you buy). Aironet is supposed to support WEP as well, but last I knew, they hadn't yet (this may have changed).
Proxim's RangeLAN2 doesn't follow the 802.11 standard, however they do have their own security built-in with a radio security ID, though I do not recall how strong this security is.