If transmission speed is not a concern (because even slow is pretty darn fast), should he buy a b card that is available, instead of a g card that might never be available (It's a 10-year old Mac), and will it likely work everywhere a g card does?
In another thread I wrote a lot, probably more than those in this group wanted to read, about b vs. g cards.
A couple months ago I was on a trip with my first laptop and a wireless b card,(generic but using prisma software, and I learned the maker too. If it matters, I'll find it.)
It worked fine in a couple netcafes, but I also stayed at a dorm and there it didn't work. The guys told me they were using g, and I should buy a g card. Which I did. (a D-link b/g card) The software interface was more comprehensive and seemed to support a lot more features, but the card itself rarely worked**. I don't think the b card ever worked, but all in all, I'm still asking, are there routers that transmit g but not b.
For now, my friend is planning to use his Mac wirelessly, if possible, at his brother's, who may not know what he is transmitting, but there are a lot of other places too that he might want to use it.
**After the second card didn't work, the guy in charge let me unplug the community computer, rarely used, and plug the cable straight into my laptop, which worked fine.
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That makes sense. I should have asked the guy at the dorm to turn on b, if it was actually not on.
There were 5 or 6 or more other people who were using the wireless with no troubles. I don't know why I had problems, but I won't be there again for at least a year, maybe never.
At the time I was confused -- I seem to forget things quickly since i turned 50 -- and thought it was the need to enter a password that required me to get the new pc card. At the netcafes, no password was required. And I knew the card that came with my laptop was an old one. (Heck the whole computer was iirc 93 dollars on ebay, including
30 dollars for shipping, but it worked fine in every other way, except maybe the microphone jack doesn't work, but the built-in mike does.)
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What Bill is saying, I think, is that as a network administrator, it's often not efficient or appropriate for a local network to use B. Your needs as an individual may be different, but you have to play well with the group!
A big issue with B - and this is what you may be remembering from the dorm - is that very few B cards can handle the newer WPA security. In our system, for example, we use WPA (WEP is not secure) but one pc with a B card only did WEP. It was not worth it to compromise the security of the whole group just to let him on. We found him an adapter.
I had an Orinoco classic B card that would do WPA security once I found the proper firmware. There were 10 versions that did not do WPA and one that did. So it's possible, just not likely.
If you need to travel and connect in various places, then you want G.
802.11b has distinct coverage advantages, and often greater channel capacity in consumer-grade access points. No one should seriously rely on embedded security in those products, WEP or WPA; a VPN (IPsec for example) solution makes more sense and scales better in a public (campus/dorm) setting.
Maybe I should add that this dorm had about 37 people, maybe 10 of whom had laptops, and probably no more than 5 were ever running at one time. Plus they had on the same line a VOIP phone used less then an hour a day, and 2 desk computers, each of them used less than an hour a day. So the network was nowhere near its capacity.
I also take issue with the words "burden" and "extra effort". I know it's common to anthropomorphise machines and electronics, but when they don't really expend extra effort (or struggle, as I read somewhere else). They do what they have the power to do, and if they can't do all that is wanted, the slow down, or stop something. Maybe sometimes they burn out, break, but that wouldn't happen in this situation.
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Maybe, but I knew this group personally, and we were all fraternal in our attitudes to each other. Perhaps they were not technical enough to realize that g could be running and b could run too if it was turned back on, but if they had known that, they would have told me to ask the guy who ran things.
But when they told me I needed g, I went out and got it. I don't think I asked the network guy if that was what I should do, and I know I didn't ask him if he could turn b back on. He never mentioned the b-g issued.
Also, I don't think security was really an issue.
I was there for 7 weeks, but other people came and went. A few of them with laptops. I won't be back any sooner than next March, and probably not even then. But if I write him or talk to him, I hope I ask him about all this.
Thanks for the technical stuff.
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The default is to enable 802.11b compatibility. I sometimes turn it off.
The problem with "b" is not speed. It's the air time it occupies. Data sent at 1Mbits/sec, the slowest 802.11b speed, occupies about 8 or 9 times as much air time as the same data sent at 6Mbits/sec, the slowest 802.11g (OFDM) speed. If the airspace is saturated with a large number of users, 802.11g can ideally handle 8 times as many users, assuming they're running at the slowest speed (a good assumption as multiple collisions will cause the access point to switch to the slowest speeds in an attempt to recover).
There are other problems with 802.11b. With 802.11b compatibility enabled in the wireless access point, all management packets and broadcasts are sent at the slowest (and longest) 1Mbit/sec speed. Turn off 802.11b compatibility, and 802.11g sends them at 6Mbits/sec, the slowest 802.11g speed.
802.11b also has problems dealing with reflections, multipath, and frequency selective fading. 802.11g OFDM modulation is far more resistant to these problems. One would assume that this would not be a common problem, but I'm finding it all too common.
For example, one of my coffee shop customers is in an octagon shaped brick building. The place is one big mess of reflections. It's even difficult to hear onself talk through all the noise and echos. I was getting erratic download speeds and even some disconnects, for no obvious reason. Monitoring the wireless router, I found far too many users connecting at 802.11b speeds. I assumed that this was caused by interference and reflections. So, I just turned off 802.11b compatibility. The disconnects instantly ceased, and the erratic performance was hugely reduced. So were the complaints.
I assumed that there would be problems with users having only 802.11b. So, I hung up a small sign, under the "we have free wi-fi" sign, that announced the 802.11b is not supported. There were a few complaints, that I "solved" by explaining why they should buy a better wireless adapter. There was also one issue that caught me by suprise. Many
802.11g USB dongles revert to 802.11b only mode if shoved into a USB
1.1 port. The device can easily do 802.11g speeds, but the authors of the device drivers seem to think that flow control is evil, and that the wireless speed should be slowed down to match the interface speed. I can see the logic, but this has given me problems with some users.
There are also some PDA's that do not support 802.11g. For example, my Verizon XV-6700 only does 802.11b, but does to WPA encryption. There are other PDA's and cell phones with similar configurations.
At this time, some of my wireless routers have 802.11b enabled, while others have it turned off. It varies by location, owner politics, and class of users. If it's a high traffic and high user count system,
802.11b is OFF. If it's light use, then I leave it on.
Greater channer capacity? In that B can handle more clients per channel? That seems to be the opposite of what I hear. I admit that I'm just parrotting what I've learned from the discussions on this forum, so if there's more to it, then please elaborate.
As far as coverage advantages - are you referring to the greater transmitting power listed for B? It seems like Jeff disabused me of that interpretation once already but I forgot the details.
No one should seriously
What are the security problems in WPA beyond cracking weak passwords ? I have not heard...
WEP, on the other hand is now well known to be crackable. You are lumping them both together?
Perhaps what you are saying is that if one is connected to a "hostile" LAN like a coffee shop, then wireless security does not protect one from threats within that LAN? And in such cases, VPN to a non- hostile (if you have one) LAN is best?
That makes sense. Sort of like saying that a deadbolt will not protect you from strangers already in your house. But that's not to say that there's no reason to lock your doors ! Or that we shouldn't use a good deadbolt instead of an easily opened door latch. Or that administrators don't prefer to control who is allowed in the LAN.
Appreciate any clarification. Since I'm responsible for the security of a small group sharing a connection, I want to know if there's something further I should be doing besides using strong pw WPA. Everyone within is trustable - a friendly LAN, if you will.
I just meant that for a given LAN PHY bandwidth, more 802.11b connections could be aggregated at 11 Mbps than at 54 MBps (unrelated to 'client' connections), assuming max rates in both formats. Capacity is obviously dependent on available resources in the access point/router such as available ram for buffers and tables and processing speed of the cpu.
Jeff says that OFDM is more robust, and perhaps the shorter packets at higher speeds suffer less from destructive multipath interference, but I have memory of analyses that show 802.11b to be generally more robust in open-air settings. He also says that slower OFDM speeds compared against equivalent DSSS speeds provide superior channel capacity; I have no experience to evaluate this.
Just a philosophy; in a setting larger than an informal group, especially where participants are not entirely trusted, use the best security available at the least cost -- e.g. a stand-alone router based on a secure o/s that can be configured and sized to the requirements of the application. I use OpenBSD, IPsec VPNs and run the access points wide open.
Thanks for the clarifications, especially on your own approach.
I conclude that for our system as well as most homes and small offices, G with WPA is still most efficient (vs B) and appropriate path to wireless security.
Most of us just don't have time to go into alternative OSs etc, but it's good to know what the serious techs are doing !
Shorter packet do have a higher probability of delivery in the presense of fixed rate interference. That's also the reason for packet fragmentation, which splits large packets into smaller pieces so that the chances of getting clobbered by interfence is less. Of course, with smaller packets, the packet overhead is increased, resulting in a loss in thruput.
The problem with 802.11b modulation methods is that an interfering RF blast at any inband frequency, during transmission, is fatal to the entire packet. The data is trashed and needs to be resent. However,
802.11g OFDM consists of 52(?) carriers, each of which carry part of the data. If one carrier gets trashed by interference or frequency selective fading, the other carriers will still make it through and get decoded.
It's not a huge difference. With 802.11b, all management packets are sent at 1Mbit/sec. That takes more airtime than the same 802.11g management packets sent at 6Mbits/sec.
A very rough indication is the difference in thruput between
11Mbits/sec 802.11b versus 12Mbits/sec 802.11g. You'll be lucky to get more than 4.5Mbits/sec thruput with 11Mbits/sec, but can easily obtain 6Mbits/sec at 12Mbits/sec. OFDM (with 802.11b compatibility off) has very close to 50% of raw data rate thruput. CCK is perhaps about 40%. Not a huge difference, but noticeable.
Also see:
These are some observations on the performance of the MIT Roofnet mesh network in real conditions. Note that it's all 802.11b. Also note the rather lousy "probability of delivery". I don't consider such chronic and typical packet losses to be "robust". Similar networks implimented using 802.11g work much better, with far less packet loss, but over a smaller range/area.
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