Frequency hopping is basically like an ordinary radio transmitter which is tuned to a different frequency every 100ms or whatever your rate is. The signal strength on each frequency is max, and if you know the hop sequence, you can follow the signal.
Direct Sequence does not hop!! It takes the input signal and combines it with a long chipping sequence in such a way that what was a peak at one frequency becomes a very low broad signal. The military like this because you can get the whole signal to lie at a lower level than rf noise - making it an absolute bugger to find, let alone read. The radio for these is much more expensive but the price is coming down.
Most of the major manufacturers sell both kinds - Symbol and Cisco being the two top brands. Symbol's kit is rebadged by people like 3Com, and Cisco bought Aironet or Telxon, before Symbol bought Telxon. Lucent do quite a good 11Mbit/s Point to Point link as well.
Starbucks are also going to roll it out in the UK as well, just a bit delayed.
802.11 is more popular (by numbers anyway) in the UK at the moment, as it has some nice peculiarities which allow very dense Access Point packing and higher range - great for use in stores and warehouses like Tesco, Sainsbury etc, but 802.11b has more potential bandwidth-wise.
Once we get onto the 25Ghz band and transmitting at 50Mbit/s the price of the lower spec kit will be easily within reach of the home user (it almost is now - I have a wireless network in my house:) but we'll always be behind the US as we are limited to 100mW so we need more AP's for the same area. Of course we won't get our brains fried as fast!
This is really the same problem as always: if you set the LAN up correctly it is pretty secure, but out of the box it isn't. The cheap 802.11 Frequency Hopping stuff is easy to monitor - strong signal strength, known hop sequences etc, but if you use 128 bit WEP, Access Control Lists and encryption over IP (IPsec or others) then you are not too open. Go to 802.11b Direct Sequence and unless you have the correct chipping set, you can often find the signal is at a lower level than ambient RF noise, which adds to the intruders problems
Anyone who allows broadcast ESS ID's or unknown MAC addresses into their network is just asking for trouble. That is like allowing an intruder to patch straight into your hub!
Follow the instructions and you make the hackers task harder - never impossible - but make it too annoying or too time-consuming and they will go on to easier targets.
I and my family went round to my brothers to see the eclipse (Edinburgh - perfect latitude)
The evening looked to be crap at first, due to too much cloud, but it cleared up at about 6.45 and the eclipse was going great guns - nice reddish tinge etc.
So we got out the BIG telescope my sister-in-law got for Christmas, and the moon looked really cool.
But weve seen it all before, so we started pointing the 'scope at other things. Like Jupiter and Saturn. I don't know how many of you guys have got a close look at them from your own backyard, but I seriously recommend it. Amazing stuff. The big 4 moons of Jupiter, and the bands of cloud very easy to see, and the rings around Saturn are astonishing.
Not so much a useful post as a waffle, but seriously - get a telescope (reasonably cheap) and take a look. Gives a good excuse to cuddle up and keep warm:)
Frog51
Moderation Flamebait?? You are joking!
on
Digital Doctoring
·
· Score: 1
Stating the truth is not flamebait - 95% of my customers are banks, hospitals and organisations with large mission critical databases. Some have even tried using MS NT clustering as a high reliability/availability solution. It has never worked.
Basically the Windows operating system is just not as solid as Unix, and Unix is not as solid as OS/400.
OS/400 can run non-stop, even during upgrades of hardware and software.
Some Unixes can give you 99.99999% uptime
Top documented MS cluster gave 99.2% uptime
This may sound like a very small difference, but when 20 minutes downtime can cost upwards of £4 million, it just makes sense to use a mature OS.
Electronic devices per se are fine in hospitals, and I tend to spend a lot of my time setting up rf networks in hospitals (802.11 kit in UK is limited to 100mW output power) with no problems - in fact we often hook heart monitors to mobile bridges so patients can be moved without having to take a trolleyload of hardware with them, or drug trolleys with a laptop and rf network card to make patient record updates easier and more accurate. Its devices with the output power of mobile phones (1/2 a watt and up) which can interfere with sensitive heart monitors.
Although I have seen a Vodafone antenna siuated on the top of the Royal Infirmary in Edinburgh!!?!
Frog51
We have found the following to be true:
on
Digital Doctoring
·
· Score: 3
o Portability - use Symbol 802.11 enabled Palm and have spread spectrum radio coverage throughout and either a telnet or html client.
o Reliability & Security - NEVER USE MICROSOFT!!! Use AS/400 if you want absolute reliability, or Unix if you want high reliability with ease/cheapness of coding/updating.
o Legal considerations - there are many ways to sign/legally encode a file...discussed elsewhere.
This only leaves the "We've always done it this way" brigade - work on them:)
To me this definitely seems to be the way to go - no more city art funded by taxes. Instead, we get art created and installed for free by nearly anonymous individuals/groups (okay, it costs them money, but that's up to them)
All the better if it is a bit quirky or whimsical - provokes thought and conversation.
This is baffling - the number of clients who we have seen happy with Exchange are far outweighed by those seriously pissed off with it. Some of our biggest deals this year have been hacking out stacks of this MS junk and popping in AS/400's with real enterprise levl software. Exchange just DOES NOT SCALE!!!
In other interesting news, Microsoft themselves had to replace W2000 and Exchange with a high end AS/400. Hee hee hee.
As part of demoing kit, I usually reflash my palm devices every time I show them to customers. It's a good way of preventing them doing things they shouldn't.
So far no problems flashing the ROM and I have done upwards of 100 wipe/reflash cycles on one device.
I spent a fair bit of my childhood in the Falklands, and with a mad keen ornithologist for a father there was much time spent in the penguin colonies getting bitten by their fleas.
Two things- penguins rarely bother looking up. They have very few predators from the sky (the local turkey buzzards will grab eggs and sickly young)
The noise of jets and helicopters spooks them so they leg it
Amusingly though, back in the days right after the conflict, a C130 hercules flanked by two F4 phantoms used to do the Christmas mail run round the settlements. They'd come in at under 50 feet, phantoms just above stall speed and hercules batting it's little engines out and pull up over each settlement to drop mail and presents.
The sudden noise used to make everyone fall over. As a young teenager I loved it:)
You receive a private email during work hours because that is when it was sent. It doesn't matter that you were actually going to look at it after work - it is on your machine now, so your employer can legally look at it.
This is seriously crap. Luckily I configure/play with the security on my company network so I am vaguely okay.
PGP good, but they can stick us in jail for not handing over our keys. This sucks.
Steganography better - if they don't know we're encrypting, they can't force us to handover keys:)
Bluetooth is one international standard. It works very well at VERY short range. It is not going to be a good setup for LANs - poor security, too slow, too unresponsive to change - but blows everything else away when it comes to phone earpieces, or scanner to portable printer connectivity. It also kills 802.11 devices in close proximity to it as its hop speed is so high.
802.11 is also international, and considerably better for a home LAN
802.11 - 2Mb Frequency Hopping - pretty solid, with good range. Not bad for industrial settings where end users have a telnet/3270/5250 application.
802.11b - 11Mb Direct Sequence - very solid, and very secure; signal can be at a lower level than rf interference, so can't be seen. Signal only appears when decoder with identical chipping set is used. I've had Quake 2 over a 5 mile link with directional antennas - no judder!
802.11b - 11Mb Frequency Hopping - An excellent choice for the home. Frequency hoppers are much cheaper than DS transmitters, and 11Mb gives much better throughput than 10BaseT (CSMA/CA overhead is less than half CSMA/CD)
802.nextgen - 25Mb radio, at 5GHz. Throughput - yummy, range - down a bit, unfortunately.
What they're doing is kinda funny and anyway if you like their music, why not buy their CD's and help support them???
I disagree with the cost of CD's (relative to the manuf. costs) but until there is a sensible way to listen to what I want, and then purchase the songs I like with no hassle and very low cost, I'm still going to download samples from mp3.com and buy the albums I like from HMV or Tower Records.
Wouldn't get them from Napster though - way too much hassle!!
Anyway - when you have a wide enough group of friends, I can get most of what I want through copying tracks from them - and that is still a legal grey area:)
Okay, a couple of points - in the UK we consistently get up to 800m with a 100mW output power with an 11Mb Symbol set, and considerably more than that with the US's 1W limit. This isn't that bad.
Also - If you need more than 20 concurrent users in one area you can place more than one Access Point at each site. I know the Airport is not quite as intelligent as the Symbol kit, but it still copes okay with this setup.
I still think that unless we go for a realistic picocell environment across the whole country then it is pointless to replace the current GSM setup - although I do want my Symbol 1740 Palm device with laser scanner and 802.11 with telnet + html browser apps to work everywhere...:)
My God - I never saw this before. I guess it has probably been discussed to death previously, but have you checked out the nutter spin doctoring on this page??
Like "it's important to note that Linux uses the same security model as the original UNIX implementations--a model that was not designed from the ground up to be secure. " and totally disregarding questions about windows security. Or "how many certified engineers are there for Linux? How easy is it to find skilled development and support people for Linux?"
Most of my team are MCSE - and they run Linux at home:) Although they all agree W2k is a massive step in the right direction.
I never realised VRML had actually died out. I find it was always a dead easy way to code, and I never found a machine that struggled with the rendering. Even the file sizes are actually pretty small if you compare trying to do a similar thing using other methods.
Examples are virtual worlds to explore, the virtual Mars project, a small app I coded to show family trees in a "Jurassic Park/I know this - this is Unix" kind of way:)
Really easy to texture/image map, light, animate etc.
The Cosmo VRML viewer works quite well on PCs now as well.
go to www.empeg.com and see what you think. 36 Gb of mp3 files in a unit that fits in your dashboard like a standard stereo, but it runs Linux and it rocks!
I zapped all my CD's onto mine, downloaded a couple of ones and put on some of my own band - it is seriously versatile!
Why - what is it about these ones that does it for the ladies?? I mean there's no blood, no beasties with fangs, no scary death scenes...oh...now I get it.
On Aironet, Lucent and Symbol kit, the loadsharing is on by default. The AP's all update each others association tables, and track signal strength - the loadsharing is done as a factor of congestion and signal quality, ie if an AP has a better connection to a mobile device it will switch across automatically.
Cisco bought Aironet, but the terms of the agreement mean that Telxon are still the easiest route to go through. Symbol also do an 11Mbit DS system, but aren't pushing it 'cos they're waiting for the 25Mbit kit, which could be out this Autumn.
This generally shouldn't become an issue, as the 802.11 standard allows for intelligent loadsharing (assuming rf coverage by more than one AP). Certainly, we like to overlap quite heavily in industrial areas - continuous coverage by 3 AP's for any mobile device pretty much guarantees robustness (for hw fail or congestion) - of course using Voice over IP over 802.11 rf does mean we need nice fast routers in there as well:)
Slashdot Mirror
2001-03-17 18:19:20 hmm - tee shirts for free. Almost worth checking out the Mir ephemeris data:)
Frog51
Frequency hopping is basically like an ordinary radio transmitter which is tuned to a different frequency every 100ms or whatever your rate is. The signal strength on each frequency is max, and if you know the hop sequence, you can follow the signal.
Direct Sequence does not hop!! It takes the input signal and combines it with a long chipping sequence in such a way that what was a peak at one frequency becomes a very low broad signal. The military like this because you can get the whole signal to lie at a lower level than rf noise - making it an absolute bugger to find, let alone read. The radio for these is much more expensive but the price is coming down.
Most of the major manufacturers sell both kinds - Symbol and Cisco being the two top brands. Symbol's kit is rebadged by people like 3Com, and Cisco bought Aironet or Telxon, before Symbol bought Telxon. Lucent do quite a good 11Mbit/s Point to Point link as well.
Frog51
Starbucks are also going to roll it out in the UK as well, just a bit delayed.
802.11 is more popular (by numbers anyway) in the UK at the moment, as it has some nice peculiarities which allow very dense Access Point packing and higher range - great for use in stores and warehouses like Tesco, Sainsbury etc, but 802.11b has more potential bandwidth-wise.
Once we get onto the 25Ghz band and transmitting at 50Mbit/s the price of the lower spec kit will be easily within reach of the home user (it almost is now - I have a wireless network in my house:) but we'll always be behind the US as we are limited to 100mW so we need more AP's for the same area. Of course we won't get our brains fried as fast!
Frog51
Just use encryption - IPSec is ideal for this sort of thing, or PGPnet. It's either that or change your working methods.
Frog51
This is really the same problem as always: if you set the LAN up correctly it is pretty secure, but out of the box it isn't. The cheap 802.11 Frequency Hopping stuff is easy to monitor - strong signal strength, known hop sequences etc, but if you use 128 bit WEP, Access Control Lists and encryption over IP (IPsec or others) then you are not too open. Go to 802.11b Direct Sequence and unless you have the correct chipping set, you can often find the signal is at a lower level than ambient RF noise, which adds to the intruders problems
Anyone who allows broadcast ESS ID's or unknown MAC addresses into their network is just asking for trouble. That is like allowing an intruder to patch straight into your hub!
Follow the instructions and you make the hackers task harder - never impossible - but make it too annoying or too time-consuming and they will go on to easier targets.
Frog51
I and my family went round to my brothers to see the eclipse (Edinburgh - perfect latitude) The evening looked to be crap at first, due to too much cloud, but it cleared up at about 6.45 and the eclipse was going great guns - nice reddish tinge etc.
So we got out the BIG telescope my sister-in-law got for Christmas, and the moon looked really cool.
But weve seen it all before, so we started pointing the 'scope at other things. Like Jupiter and Saturn. I don't know how many of you guys have got a close look at them from your own backyard, but I seriously recommend it. Amazing stuff. The big 4 moons of Jupiter, and the bands of cloud very easy to see, and the rings around Saturn are astonishing.
Not so much a useful post as a waffle, but seriously - get a telescope (reasonably cheap) and take a look. Gives a good excuse to cuddle up and keep warm:)
Frog51
Stating the truth is not flamebait - 95% of my customers are banks, hospitals and organisations with large mission critical databases. Some have even tried using MS NT clustering as a high reliability/availability solution. It has never worked.
Basically the Windows operating system is just not as solid as Unix, and Unix is not as solid as OS/400.
OS/400 can run non-stop, even during upgrades of hardware and software.
Some Unixes can give you 99.99999% uptime
Top documented MS cluster gave 99.2% uptime
This may sound like a very small difference, but when 20 minutes downtime can cost upwards of £4 million, it just makes sense to use a mature OS.
Flamebait - I think not:)
Frog51
Electronic devices per se are fine in hospitals, and I tend to spend a lot of my time setting up rf networks in hospitals (802.11 kit in UK is limited to 100mW output power) with no problems - in fact we often hook heart monitors to mobile bridges so patients can be moved without having to take a trolleyload of hardware with them, or drug trolleys with a laptop and rf network card to make patient record updates easier and more accurate. Its devices with the output power of mobile phones (1/2 a watt and up) which can interfere with sensitive heart monitors.
Although I have seen a Vodafone antenna siuated on the top of the Royal Infirmary in Edinburgh!!?!
Frog51
o Portability - use Symbol 802.11 enabled Palm and have spread spectrum radio coverage throughout and either a telnet or html client.
o Reliability & Security - NEVER USE MICROSOFT!!! Use AS/400 if you want absolute reliability, or Unix if you want high reliability with ease/cheapness of coding/updating.
o Legal considerations - there are many ways to sign/legally encode a file...discussed elsewhere.
This only leaves the "We've always done it this way" brigade - work on them:)
Frog51
To me this definitely seems to be the way to go - no more city art funded by taxes. Instead, we get art created and installed for free by nearly anonymous individuals/groups (okay, it costs them money, but that's up to them)
All the better if it is a bit quirky or whimsical - provokes thought and conversation.
Frog51
This is baffling - the number of clients who we have seen happy with Exchange are far outweighed by those seriously pissed off with it. Some of our biggest deals this year have been hacking out stacks of this MS junk and popping in AS/400's with real enterprise levl software.
Exchange just DOES NOT SCALE!!!
In other interesting news, Microsoft themselves had to replace W2000 and Exchange with a high end AS/400. Hee hee hee.
Frog51
As part of demoing kit, I usually reflash my palm devices every time I show them to customers. It's a good way of preventing them doing things they shouldn't.
So far no problems flashing the ROM and I have done upwards of 100 wipe/reflash cycles on one device.
Frog51
I spent a fair bit of my childhood in the Falklands, and with a mad keen ornithologist for a father there was much time spent in the penguin colonies getting bitten by their fleas.
Two things-
penguins rarely bother looking up. They have very few predators from the sky (the local turkey buzzards will grab eggs and sickly young)
The noise of jets and helicopters spooks them so they leg it
Amusingly though, back in the days right after the conflict, a C130 hercules flanked by two F4 phantoms used to do the Christmas mail run round the settlements. They'd come in at under 50 feet, phantoms just above stall speed and hercules batting it's little engines out and pull up over each settlement to drop mail and presents.
The sudden noise used to make everyone fall over. As a young teenager I loved it:)
Frog51
You receive a private email during work hours because that is when it was sent. It doesn't matter that you were actually going to look at it after work - it is on your machine now, so your employer can legally look at it.
This is seriously crap. Luckily I configure/play with the security on my company network so I am vaguely okay.
PGP good, but they can stick us in jail for not handing over our keys. This sucks.
Steganography better - if they don't know we're encrypting, they can't force us to handover keys:)
Frog51
Well - to start:
Bluetooth is one international standard. It works very well at VERY short range. It is not going to be a good setup for LANs - poor security, too slow, too unresponsive to change - but blows everything else away when it comes to phone earpieces, or scanner to portable printer connectivity. It also kills 802.11 devices in close proximity to it as its hop speed is so high.
802.11 is also international, and considerably better for a home LAN
802.11 - 2Mb Frequency Hopping - pretty solid, with good range. Not bad for industrial settings where end users have a telnet/3270/5250 application.
802.11b - 11Mb Direct Sequence - very solid, and very secure; signal can be at a lower level than rf interference, so can't be seen. Signal only appears when decoder with identical chipping set is used. I've had Quake 2 over a 5 mile link with directional antennas - no judder!
802.11b - 11Mb Frequency Hopping - An excellent choice for the home. Frequency hoppers are much cheaper than DS transmitters, and 11Mb gives much better throughput than 10BaseT (CSMA/CA overhead is less than half CSMA/CD)
802.nextgen - 25Mb radio, at 5GHz. Throughput - yummy, range - down a bit, unfortunately.
Cat 5 my house? No need with RF!!!
Frog51
What they're doing is kinda funny and anyway if you like their music, why not buy their CD's and help support them???
I disagree with the cost of CD's (relative to the manuf. costs) but until there is a sensible way to listen to what I want, and then purchase the songs I like with no hassle and very low cost, I'm still going to download samples from mp3.com and buy the albums I like from HMV or Tower Records.
Wouldn't get them from Napster though - way too much hassle!!
Anyway - when you have a wide enough group of friends, I can get most of what I want through copying tracks from them - and that is still a legal grey area:)
Frog51
Okay, a couple of points - in the UK we consistently get up to 800m with a 100mW output power with an 11Mb Symbol set, and considerably more than that with the US's 1W limit. This isn't that bad.
Also - If you need more than 20 concurrent users in one area you can place more than one Access Point at each site. I know the Airport is not quite as intelligent as the Symbol kit, but it still copes okay with this setup.
I still think that unless we go for a realistic picocell environment across the whole country then it is pointless to replace the current GSM setup - although I do want my Symbol 1740 Palm device with laser scanner and 802.11 with telnet + html browser apps to work everywhere...:)
Frog51
My God - I never saw this before. I guess it has probably been discussed to death previously, but have you checked out the nutter spin doctoring on this page??
Like "it's important to note that Linux uses the same security model as the original UNIX implementations--a model that was not designed from the ground up to be secure. " and totally disregarding questions about windows security. Or "how many certified engineers are there for Linux? How easy is it to find skilled development and support people for Linux?"
Most of my team are MCSE - and they run Linux at home:) Although they all agree W2k is a massive step in the right direction.
Frog51
Come on - I thought "Friends" was a staple TV show for all us 20something techy geeks:)
Frog51
I never realised VRML had actually died out. I find it was always a dead easy way to code, and I never found a machine that struggled with the rendering. Even the file sizes are actually pretty small if you compare trying to do a similar thing using other methods.
Examples are virtual worlds to explore, the virtual Mars project, a small app I coded to show family trees in a "Jurassic Park/I know this - this is Unix" kind of way:)
Really easy to texture/image map, light, animate etc.
The Cosmo VRML viewer works quite well on PCs now as well.
Frog51
go to www.empeg.com and see what you think. 36 Gb of mp3 files in a unit that fits in your dashboard like a standard stereo, but it runs Linux and it rocks!
I zapped all my CD's onto mine, downloaded a couple of ones and put on some of my own band - it is seriously versatile!
Frog51
Why - what is it about these ones that does it for the ladies?? I mean there's no blood, no beasties with fangs, no scary death scenes...oh...now I get it.
Frog51
On Aironet, Lucent and Symbol kit, the loadsharing is on by default. The AP's all update each others association tables, and track signal strength - the loadsharing is done as a factor of congestion and signal quality, ie if an AP has a better connection to a mobile device it will switch across automatically.
Frog51
Frog51
Cisco bought Aironet, but the terms of the agreement mean that Telxon are still the easiest route to go through.
Symbol also do an 11Mbit DS system, but aren't pushing it 'cos they're waiting for the 25Mbit kit, which could be out this Autumn.
Lucent do a good one too.
Frog51
Frog51
This generally shouldn't become an issue, as the 802.11 standard allows for intelligent loadsharing (assuming rf coverage by more than one AP).
Certainly, we like to overlap quite heavily in industrial areas - continuous coverage by 3 AP's for any mobile device pretty much guarantees robustness (for hw fail or congestion) - of course using Voice over IP over 802.11 rf does mean we need nice fast routers in there as well:)
Frog51
Frog51