note: what are commonly reffered to today as hubs and switches are considered to be repeaters and bridges respectively by the standard.
You need to remember ethernet is a shared bus technology, using CSMA/CD for collisions. Historically yes, theese days no.
Old fassioned 10BASE5/10BASE2 (which are pretty much the same other than the cable) was a shared bus technology. Busses could be joined with either repeaters (which made the busses into a single collision domain) or bridges (which made each of thier ports a seperate collison domain)
10BASE-T and the various 10 megabit fiber standards supported both CSMA/CD and full duplex links. However there was no autonegotiation at this time and hubs were far more common than switches so 10BASE-T was usually run half duplex.
Fast ethernet supports both CSMA/CD and full duplex. Any reasonablly recent 100BASE-T NICs and switches will support full duplex and will autonegotiate full duplex mode by default. CSMA/CD is used primerally with hubs (which have mostly dissapeared off the market as switch prices have come down) and possiblly with other old or weird equipmen.
1000BASE-T supports both CSMA/CD and full duplex but afaict is very rarely used in CSMA/CD mode.
note: in this post I will use the term bandwidth in the classical communication theory sense and use the term bitrate for what computer geeks often reffer to as bandwidth.
If we assume a very pessimistic signal to noise ratio of 1:1, the SH theorem says that the cable's bandwidth in hertz will be the same as the cable's bandwidth in bps. If we assume a more realistic SNR but also assume real modern modulation schemes (which can't reach that theoritical limit) then the channels maximum bitrate is likely to be arround 5-10* times the bandwidth since you can have more than one bit per symbol.
Also a cable does not have to be just one channel, your typical cat5 cable for example has 4 pairs each of which can be used as a seperate channel.
It was through the techniques of multiple bits per sybol and aggregating multiple pairs that we got first gigabit over cat5 (though 5e is reccomended for long reliable links) and then 10 gigabit through cat 6 (though IIRC it's been too much of a power hog for wide deployment, one way to increase SNR is to throw power at the problem).
However I think it is fair to say that we have mostly used up the potential for expansion in the direction of more bits per symbol (there is a big diminishing returns issue, each extra bit you add to a symbol DOUBLES the transmit power you need to maintain adequate signal to noise ratio,). More pairs is a possibility but it's going to get unweildly pretty quick (can you imagine hooking up your 1 terabit link with a 400 pair cat6a cable? ).
Fiber has it's own issues ofc, it has insane bandwidth but actually using that bandwith is limited by the need to interface it to electronics. Most of the current 100 gigabit proposals seem to be based on bonding up multiples of 10 gigabit stuff (though be doing it at a lower level I suspect they can get a better efficiancy than ordinary link aggregation) and then either running them through multiple fibers or using WDM to put them onto a single fiber.
*low number is a figure common with real multi-level encoding schemes, high figure is a guestimate (and probablly a pretty optimistic one)
Gigabit cat5e/6 costs more than old style cat5 Can you even buy old style cat5 anymore? almost all the cable I see for sale nowdays is cat5e or cat6 (cat6 being a bit more expensive than 5e but not hugely so)
Still, for most business uses, I tend to say that even 10meg connections are more than enough for most users. Seriously, we still occasionally find a 10 meg hub with some users on it. I know here at the university of machester most ports are still 100 megabit and a few are still 10 megabit. I'm sure there is the odd gigabit port arround but as you say for most people 10 megabit is sufficiant (though sometimes annoying) and 100 megabit is more than enough.
What I think fiber to the desktop needs is the equivalent to 10baseT - an open, low cost standard that is cheap and easy to use. And to make it cheap you need a lot of users, and that means you need a killer application that means a lot of users need more than gigabit to the desktop.
While we have retained the ethernet name and frame format CSMA/CD has pretty much gone the way of the dodo (it's supported but virtually never used at gigabit and not supported at all at 10 gigabit)
Token ring gives each device on the ring roughly equal time, I'd imagine switched ethernet with a decent switch would have similar behaviour. I beleive some of them can also prioritise data.
they yell for a bigger integer before "bit" instead of changing technology. because throwing bandwidth at the problem typically solves it without needing to redesign the network or make value judgements about whose data is more important.
I don't see gigabit being superseeded for connections to end systems anytime soon. 10GBASE-CX requires expensive cable and has annoying run-length limitations. IIRC 10GBASE-T is a power hog. Fiber is both expensive and a PITA for such applications (I very much doubt fiber patch cords would last very long in a typical desktop environment)
It might be an idea to select gigabit switches with the capability to handle 10 gigabit uplinks though.
Sellers should have the option of creating a 'rolling auction' where each time a bid is placed the auction close is reset a day into the future or maybe 8 hours... I dunno whatever. Then sniping becomes a much weaker strategy because even if you bid at the last second everyone else has a reasonable period of time to re-consider their bids. Personally I would avoid such an auction (unless it was the only way to get a rare item) because I would know that irrational twits would most likely win and because it would make dealing with trying to buy one of a load of similar items a PITA.
While I don't particularlly like the current ebay format I think an indeterminate end time would piss off a lot of buyers (and the more buyers you have the more likely you will have some buyers who think the item is valuable) while a sealed bid system would extract less money from irrational twits.
Cat5e is what you buy and install. Personally if I was specifying new fixed cabling in a commercial environment (at home I use 5e because I could get it in a smaller reel, and I don't see any need to run at more than 100 megabit) I would be specifying cat6 (or maybe even 6a but that still seems to be difficult to obtain). The price difference is relative small (especially when you consider that the cable is probablly a small part of the cost of the wiring installation job), having some headroom is generally a good thing (degredation is at least to some extent cumulative) and it may allow for 10 gigabit in future (though it's hard to say as 10 gigabit is still pretty immature and iirc 10GBASE-T is a massive power hog).
As long as you made electrically solid joints and didn't untwist too much it should be fine. The wires untwist a bit in a wallport or patch panel port too and it's not too much of a problem.
The real problems are going to start if you either have too much untwisted cable (just how much is too much is difficult to quantify) or your joints are bad.
The term coax covers a whole range of cables from ones inferior to cat5e to ones far supirior. From a quick check online it seems RG-58 (thinnet coax) is fairly lossy at 100MHz and very lossy at 1GHz, I can't seem to find any decent specs online for cat5 to compare but I suspect they are pretty similar.
I don't think BNC connectors are particularlly inconviniant, they are solid and reasonablly sized for the cable sizes they were used with. And unlike with cat5 you don't have to mess arround arranging conductors before terminating.
The real problem with coax was that a combination of high cable costs and the practicailities of the standards and equipment developed for it basically forced you to run it as a bus network. Bus networks suck for a few reasons.
1: all devices on the bus have to work at the same speed, there is no opertunity for phased in upgrades. 2: One bad device or connection can easilly bring down the entire bus 3: the topology gets less and less practical as speed increases reduce the minimum packet length (gigabit ethernet has to use a dirty hack to support half duplex mode and is very rarely used in that mode)
I would make sure that all network devices are showing 100 MB connection, they may have failed pairs that dropped to 10 MB, and never noticed. Ethernet autoengotiation DOES NOT take account of the condition of the channel.
I've seen in practice 100 megabit over a bad channel (split pairs), it doesn't fall back, it just becomes unusuablly lossy (that is small pings get through sometimes, big packets don't stand a chance).
The trouble with ethernet is it's negotiation scheme only takes account of the capability of the end devices, NOT the conditions on the line in between them (this is different from something like modern ADSL which negotiates a rate based on line conditions).
So if your cable is not up to gigabit (cat5 should theoretically support gigabit but only if it's installed absoloutely to spec and the run isn't too long), you put gigabit hardware at both ends and you don't manually (which opens it's own can of worms e.g. duplex mismatch issues) force the speed down it will try to run at gigabit and end up with a horrible error rate.
To put it another way for small networks with unmanaged switches make sure you stick to 100 megabit switches unless you are sure your wiring is good for gigabit.
Oh and make damn sure you don't have any "split pairs" (two lines that should be on the same pair on different pairs), those will cause horrible error rate even at 100 megabit.
Does anyone here have a copy of an exiting MS starter edition of XP or vista (only sold in the third world though I belive it is availible on MSDN) and fancy trying to figure out what they are counting.
With an office suite an incompatibility risk in upgrading rather goes with the territory. Any change to the layout engine can turn your perfectly arranged document into a messy POS.
Do we really have any gaurantee that openoffice's layout engine will have consistant behaviour for the next few decades either?
meh, how much support do most buisness users really get from MS anyway? In my experiance with mass market software (specialist software is a different ball game) contacting a vendor for support is a last resort.
Isn't he still "a post-graduate"? The term postgraduate usually reffers to someone who has completed thier bachelors degree (or completed a direct to masters program) and is studying towards a higher degree (masters or phd).
After completing thier phd if the person stays in academia they will typically end up with a temporary reaseach job. Such people are generally reffered to as "postdocs".
Eventually a few of those postdocs (most will leave academia and go into industry) will then get permanent jobs as lecturers and eventually a few of those lecturers will get jobs as proffessors.
note: this is based on the UK system which is the relevent one for this subject, I don't know if and how US conventions differ. It is also based on the system as it stands today, I don't know how much things have changed since hawkings day.
If you extend them with diagonals, you can still make more lower-case. i've never seen a 7-segment display extended with just diagonals.
If you go to the common 14-segment starburst you can make a very respectable looking set of uppercase letters, see for example http://www.mitt-eget.com/displays/fourteen.shtml#set2 . Some lower case letters OTOH would be pretty damn hard to do well and/or would end up raised off the baseline.
I don't see how any type of legal "problems" stated should contribute to adding restrictions to some countries in selling e-books. Why can Amazon sell books globally? Amazon has to follow the same laws and yet is able to ship me any product I desire and am able to pay for. The reason is that copyright as the name suggests controls the activity of copying.
Afaict in the US anyone can buy books and resell them without the need for a special agreement with the publisher. Importing them into your country may or may not be legal (IANAL but I belive in the EU you can import books that aren't authorised for the EU for personal use but not for resale) but that is not amazons problem.
OTOH with digital distribution the distributor is also nessacerally the copier. That means they have to have an explicit agreement with the copyright holder to make those copies. If that agreement says they must take reasonable steps to prevent sale to non-us residents then that is what they must do.
The publishers in turn are often bound by agreements with the author and the author is likely to be bound by exclusive agreements with other publishers for other regions (and even if they are not already bound by such agreements they may want to keep the ability to enter into such agreements in future).
On 7 segment LEDs (used for digits), you can make more lower-case than upper-case chars Afaict it's pretty much a wash, some letters can be represented better in uppercase some better in lowercase, wikipedia gives lists of approximately equal length for "unambiguous and intuitive" representations of both cases but i'm not sure I agree with thier lists.
Also some of the lower case letters that can be represented end up raised off the baseline to accomodate thier descenders (yuck).
Most systems i've seen that use 7-segment displays to show alphanumerics (usually hexadecimal) use a mixture of upper and lower case depending on which is represented better.
What I think would happen though if copyright were to disapear is that certain things will dissapear or at least become far less common (some may be produced through subsidies).
Think of the staff involved in the production of a convincing movie or a story based 3D game. A large staff is required, some creative but often the majority doing gruntwork to realise the vision of those leading the project.
The same applies in the software world, some types of software are mostly gruntwork to produce and unsurprisingly such areas are often poorly served by FOSS (particularlly when the grunt work has to be done by people other than programmers, e.g. tax software)
stopping pirate games logging in to the online service is easy enough, just enforce a "one online session per key" policy. Do some very basic key checking (maybe a check digit) in the client but leave the real checking to the server so the pirates can't dissasemble it. Maybe even consider not having an algorithm at all and just comparing the key against a DB of valid keys.
Stopping people who do have valid unique keys using modified clients is much harder but that is an anti-cheat issue not an anti-pirate issue.
Amtrak's Empire Builder from the Twin Cities to Chicago is almost always packed. You usually can't get a ticket within a month of travel. I guess the question then would be why the hell aren't they running longer/more trains.
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note: what are commonly reffered to today as hubs and switches are considered to be repeaters and bridges respectively by the standard.
You need to remember ethernet is a shared bus technology, using CSMA/CD for collisions.
Historically yes, theese days no.
Old fassioned 10BASE5/10BASE2 (which are pretty much the same other than the cable) was a shared bus technology. Busses could be joined with either repeaters (which made the busses into a single collision domain) or bridges (which made each of thier ports a seperate collison domain)
10BASE-T and the various 10 megabit fiber standards supported both CSMA/CD and full duplex links. However there was no autonegotiation at this time and hubs were far more common than switches so 10BASE-T was usually run half duplex.
Fast ethernet supports both CSMA/CD and full duplex. Any reasonablly recent 100BASE-T NICs and switches will support full duplex and will autonegotiate full duplex mode by default. CSMA/CD is used primerally with hubs (which have mostly dissapeared off the market as switch prices have come down) and possiblly with other old or weird equipmen.
1000BASE-T supports both CSMA/CD and full duplex but afaict is very rarely used in CSMA/CD mode.
10GBASE-T and above support full duplex only.
and you will notice that having killed off token ring at the low end ethernet is now taking over at the higher end too ;)
note: in this post I will use the term bandwidth in the classical communication theory sense and use the term bitrate for what computer geeks often reffer to as bandwidth.
If we assume a very pessimistic signal to noise ratio of 1:1, the SH theorem says that the cable's bandwidth in hertz will be the same as the cable's bandwidth in bps.
If we assume a more realistic SNR but also assume real modern modulation schemes (which can't reach that theoritical limit) then the channels maximum bitrate is likely to be arround 5-10* times the bandwidth since you can have more than one bit per symbol.
Also a cable does not have to be just one channel, your typical cat5 cable for example has 4 pairs each of which can be used as a seperate channel.
It was through the techniques of multiple bits per sybol and aggregating multiple pairs that we got first gigabit over cat5 (though 5e is reccomended for long reliable links) and then 10 gigabit through cat 6 (though IIRC it's been too much of a power hog for wide deployment, one way to increase SNR is to throw power at the problem).
However I think it is fair to say that we have mostly used up the potential for expansion in the direction of more bits per symbol (there is a big diminishing returns issue, each extra bit you add to a symbol DOUBLES the transmit power you need to maintain adequate signal to noise ratio,). More pairs is a possibility but it's going to get unweildly pretty quick (can you imagine hooking up your 1 terabit link with a 400 pair cat6a cable? ).
Fiber has it's own issues ofc, it has insane bandwidth but actually using that bandwith is limited by the need to interface it to electronics. Most of the current 100 gigabit proposals seem to be based on bonding up multiples of 10 gigabit stuff (though be doing it at a lower level I suspect they can get a better efficiancy than ordinary link aggregation) and then either running them through multiple fibers or using WDM to put them onto a single fiber.
*low number is a figure common with real multi-level encoding schemes, high figure is a guestimate (and probablly a pretty optimistic one)
Gigabit cat5e/6 costs more than old style cat5
Can you even buy old style cat5 anymore? almost all the cable I see for sale nowdays is cat5e or cat6 (cat6 being a bit more expensive than 5e but not hugely so)
Still, for most business uses, I tend to say that even 10meg connections are more than enough for most users. Seriously, we still occasionally find a 10 meg hub with some users on it.
I know here at the university of machester most ports are still 100 megabit and a few are still 10 megabit. I'm sure there is the odd gigabit port arround but as you say for most people 10 megabit is sufficiant (though sometimes annoying) and 100 megabit is more than enough.
What I think fiber to the desktop needs is the equivalent to 10baseT - an open, low cost standard that is cheap and easy to use.
And to make it cheap you need a lot of users, and that means you need a killer application that means a lot of users need more than gigabit to the desktop.
10 years, maybe 15, and we'll all be on fiber.
On what do you base this claim?
How do you propose to get arround the problem that fiber patch cords are easilly damaged?
What applications do you think will require this kind of bandwidth? HD video with moderate compression should easilly fit into a gigabit.
While we have retained the ethernet name and frame format CSMA/CD has pretty much gone the way of the dodo (it's supported but virtually never used at gigabit and not supported at all at 10 gigabit)
Token ring gives each device on the ring roughly equal time, I'd imagine switched ethernet with a decent switch would have similar behaviour. I beleive some of them can also prioritise data.
they yell for a bigger integer before "bit" instead of changing technology.
because throwing bandwidth at the problem typically solves it without needing to redesign the network or make value judgements about whose data is more important.
I don't see gigabit being superseeded for connections to end systems anytime soon. 10GBASE-CX requires expensive cable and has annoying run-length limitations. IIRC 10GBASE-T is a power hog. Fiber is both expensive and a PITA for such applications (I very much doubt fiber patch cords would last very long in a typical desktop environment)
It might be an idea to select gigabit switches with the capability to handle 10 gigabit uplinks though.
Sellers should have the option of creating a 'rolling auction' where each time a bid is placed the auction close is reset a day into the future or maybe 8 hours ... I dunno whatever. Then sniping becomes a much weaker strategy because even if you bid at the last second everyone else has a reasonable period of time to re-consider their bids.
Personally I would avoid such an auction (unless it was the only way to get a rare item) because I would know that irrational twits would most likely win and because it would make dealing with trying to buy one of a load of similar items a PITA.
While I don't particularlly like the current ebay format I think an indeterminate end time would piss off a lot of buyers (and the more buyers you have the more likely you will have some buyers who think the item is valuable) while a sealed bid system would extract less money from irrational twits.
Cat5e is what you buy and install.
Personally if I was specifying new fixed cabling in a commercial environment (at home I use 5e because I could get it in a smaller reel, and I don't see any need to run at more than 100 megabit) I would be specifying cat6 (or maybe even 6a but that still seems to be difficult to obtain). The price difference is relative small (especially when you consider that the cable is probablly a small part of the cost of the wiring installation job), having some headroom is generally a good thing (degredation is at least to some extent cumulative) and it may allow for 10 gigabit in future (though it's hard to say as 10 gigabit is still pretty immature and iirc 10GBASE-T is a massive power hog).
As long as you made electrically solid joints and didn't untwist too much it should be fine. The wires untwist a bit in a wallport or patch panel port too and it's not too much of a problem.
The real problems are going to start if you either have too much untwisted cable (just how much is too much is difficult to quantify) or your joints are bad.
The term coax covers a whole range of cables from ones inferior to cat5e to ones far supirior. From a quick check online it seems RG-58 (thinnet coax) is fairly lossy at 100MHz and very lossy at 1GHz, I can't seem to find any decent specs online for cat5 to compare but I suspect they are pretty similar.
I don't think BNC connectors are particularlly inconviniant, they are solid and reasonablly sized for the cable sizes they were used with. And unlike with cat5 you don't have to mess arround arranging conductors before terminating.
The real problem with coax was that a combination of high cable costs and the practicailities of the standards and equipment developed for it basically forced you to run it as a bus network. Bus networks suck for a few reasons.
1: all devices on the bus have to work at the same speed, there is no opertunity for phased in upgrades.
2: One bad device or connection can easilly bring down the entire bus
3: the topology gets less and less practical as speed increases reduce the minimum packet length (gigabit ethernet has to use a dirty hack to support half duplex mode and is very rarely used in that mode)
I would make sure that all network devices are showing 100 MB connection, they may have failed pairs that dropped to 10 MB, and never noticed.
Ethernet autoengotiation DOES NOT take account of the condition of the channel.
I've seen in practice 100 megabit over a bad channel (split pairs), it doesn't fall back, it just becomes unusuablly lossy (that is small pings get through sometimes, big packets don't stand a chance).
The trouble with ethernet is it's negotiation scheme only takes account of the capability of the end devices, NOT the conditions on the line in between them (this is different from something like modern ADSL which negotiates a rate based on line conditions).
So if your cable is not up to gigabit (cat5 should theoretically support gigabit but only if it's installed absoloutely to spec and the run isn't too long), you put gigabit hardware at both ends and you don't manually (which opens it's own can of worms e.g. duplex mismatch issues) force the speed down it will try to run at gigabit and end up with a horrible error rate.
To put it another way for small networks with unmanaged switches make sure you stick to 100 megabit switches unless you are sure your wiring is good for gigabit.
Oh and make damn sure you don't have any "split pairs" (two lines that should be on the same pair on different pairs), those will cause horrible error rate even at 100 megabit.
still that doesn't tell us what IS included, a ty
Does anyone here have a copy of an exiting MS starter edition of XP or vista (only sold in the third world though I belive it is availible on MSDN) and fancy trying to figure out what they are counting.
With an office suite an incompatibility risk in upgrading rather goes with the territory. Any change to the layout engine can turn your perfectly arranged document into a messy POS.
Do we really have any gaurantee that openoffice's layout engine will have consistant behaviour for the next few decades either?
meh, how much support do most buisness users really get from MS anyway? In my experiance with mass market software (specialist software is a different ball game) contacting a vendor for support is a last resort.
Isn't he still "a post-graduate"?
The term postgraduate usually reffers to someone who has completed thier bachelors degree (or completed a direct to masters program) and is studying towards a higher degree (masters or phd).
After completing thier phd if the person stays in academia they will typically end up with a temporary reaseach job. Such people are generally reffered to as "postdocs".
Eventually a few of those postdocs (most will leave academia and go into industry) will then get permanent jobs as lecturers and eventually a few of those lecturers will get jobs as proffessors.
note: this is based on the UK system which is the relevent one for this subject, I don't know if and how US conventions differ. It is also based on the system as it stands today, I don't know how much things have changed since hawkings day.
If you extend them with diagonals, you can still make more lower-case.
i've never seen a 7-segment display extended with just diagonals.
If you go to the common 14-segment starburst you can make a very respectable looking set of uppercase letters, see for example http://www.mitt-eget.com/displays/fourteen.shtml#set2 . Some lower case letters OTOH would be pretty damn hard to do well and/or would end up raised off the baseline.
I don't see how any type of legal "problems" stated should contribute to adding restrictions to some countries in selling e-books. Why can Amazon sell books globally? Amazon has to follow the same laws and yet is able to ship me any product I desire and am able to pay for.
The reason is that copyright as the name suggests controls the activity of copying.
Afaict in the US anyone can buy books and resell them without the need for a special agreement with the publisher. Importing them into your country may or may not be legal (IANAL but I belive in the EU you can import books that aren't authorised for the EU for personal use but not for resale) but that is not amazons problem.
OTOH with digital distribution the distributor is also nessacerally the copier. That means they have to have an explicit agreement with the copyright holder to make those copies. If that agreement says they must take reasonable steps to prevent sale to non-us residents then that is what they must do.
The publishers in turn are often bound by agreements with the author and the author is likely to be bound by exclusive agreements with other publishers for other regions (and even if they are not already bound by such agreements they may want to keep the ability to enter into such agreements in future).
On 7 segment LEDs (used for digits), you can make more lower-case than upper-case chars
Afaict it's pretty much a wash, some letters can be represented better in uppercase some better in lowercase, wikipedia gives lists of approximately equal length for "unambiguous and intuitive" representations of both cases but i'm not sure I agree with thier lists.
Also some of the lower case letters that can be represented end up raised off the baseline to accomodate thier descenders (yuck).
Most systems i've seen that use 7-segment displays to show alphanumerics (usually hexadecimal) use a mixture of upper and lower case depending on which is represented better.
What I think would happen though if copyright were to disapear is that certain things will dissapear or at least become far less common (some may be produced through subsidies).
Think of the staff involved in the production of a convincing movie or a story based 3D game. A large staff is required, some creative but often the majority doing gruntwork to realise the vision of those leading the project.
The same applies in the software world, some types of software are mostly gruntwork to produce and unsurprisingly such areas are often poorly served by FOSS (particularlly when the grunt work has to be done by people other than programmers, e.g. tax software)
stopping pirate games logging in to the online service is easy enough, just enforce a "one online session per key" policy. Do some very basic key checking (maybe a check digit) in the client but leave the real checking to the server so the pirates can't dissasemble it. Maybe even consider not having an algorithm at all and just comparing the key against a DB of valid keys.
Stopping people who do have valid unique keys using modified clients is much harder but that is an anti-cheat issue not an anti-pirate issue.
because digital /robotic writing must contain segments no matter how fine
However it is certainly plausible that they are lost in the noise.
Amtrak's Empire Builder from the Twin Cities to Chicago is almost always packed. You usually can't get a ticket within a month of travel.
I guess the question then would be why the hell aren't they running longer/more trains.
Are you planning to enter european parliment candidates in any other countries and/or do you have affiliated parties in other countries?