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New Look at ADSL2
genrader writes "broadbandreports.com just posted a news article which had an interesting story about the new ADSL2, which should be approved in 2003. They say it should be backward compatible with current hardware. It seems pretty interesting. ISP-Planet has the featured in-depth look at it, so you might want to see if it is of any intrest to you."
The increases in performance and range are pretty minimal. An additional 50kbps and 600ft of range isn't all that impressive, although the fact that it is backwards compatible with some existing hardware is semi-promising.
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Anyway, here's some extra info on ADSL2, or G.bis that i dug up:
http://www.aware.com/products/DSL/gbisadsl2.htm
http://www.convergedigest.com/Silicon/siliconarti
http://www.dslprime.com/a/adsl21.pdf(sorry about the pdf)
The result is a far greater flexibility with downstream data rates:
20 Mbps on 2 bonded pairs
30 Mbps on 3 bonded pairs
40 Mbps on 4 bonded pairs
So basically you get 10Mbps per phone line tops over the 1.5 we max out at now.
First of all, the story at broadbandreports.com is nothing but a short blurb about the story at ISP-Planet.
Second, the people who posted comments didn't read it. Not sure what the original author meant by a 50kbps increase, but earlier in the article he mentions a doubling of the frequency used resulting in a doubling of the downstream bandwidth. That's significant to me.
Remember your high-school geometry , area of a circle is pi(r^2)
So the 6% ( ? ) increase in range translates to a more than 12% increase in coverage area. It's not as small as first it appears.
The fact that no one understands you doesn't mean you're an artist.
The article says that there WILL be an increase in service radius by 6% from the telco loop to your home. Which translates into bigger area of service (~2.5 mi.)
Live for the present, learn from the past, and dream of the future!
Over here in the Maldives we pay ~USD45 to every 250MB for a 256kbps DSL line. When newer better technology comes in that price is going to sky-rocket. When are the enablers of technology going to start thinking about moderating that which they breed?
Just because you're paranoid doesn't mean there isn't an invisible demon about to eat your face
All this stuff is down at the physical layer. There's no mention of the higher layers; apparently we're still stuck with PPPoE, a login mechanism, and client software.
The big win with this thing will be the improved diagnostics, along with slightly better noise immunity and the power-save modes.
I've had Telus, and while one person's experience does not a rule make, it was far, FAR worse.
Unlike Shaw, Telus' dynamic IPs actually change fairly frequently. Yes, "no servers", it's residential service - fine. But if you're going to change our IPs once or twice a day, make sure that the bloody DHCP servers aren't offline more often than they're up. In the four months I was with Telus, I was unable to get online at all for more than 40% of it... This is also because my DSL modem simply died, and they refused to give me a replacement until about three weeks after I reported the problem initially.. They said they'd send someone over three times, as they wouldn't simply take my word that the modem was fried, and the techs never came. After two weeks of "When would you like an appointment? Okay, we'll send someone then", I called up Shaw, had it installed the very next day, and when I finally did get a Telus person over after another week, I took the replacement rental modem, verified that it worked, then put it back in the box before giving it back to them at the end of the month.
Even when Telus *was* working, they limit the downstream bandwidth to approximately 768 kbps. This is great for the web, certainly, but when downloading stuff from fast servers (software updates), the fact that it goes about four times faster with Shaw means that you're staring as the file downloads for a minute rather than fifteen or so seconds. This adds up, believe it or not. (And it's not worth finding something else to do for those 60 seconds, unless it's trolling on Slashdot.)
Given that after bundling the internet with my cable Shaw is significantly cheaper, and that I've not had a bad experience with Shaw in the four or so years I've been a customer, I heartily endorse them to everyone.
The only wing of Telus I am happy with is their cellular service, incidentally the only non-union part of the company. Who'd have thunk it?
From AWARE (the developer of the standard)'s site
ADSL2+ is an extension of the new ADSL2 standard planned for consent at the ITU in early 2003. ADSL2+ will allow for doubling of ADSL2 bandwidth from 1.1 MHz to 2.2 MHz, effectively doubling the maximum downstream data rate to over 20 Mbps. The data rate increase will only be effective on loops shorter than 8,000 feet. This extension to ADSL2 has often been called ADSL+ in technical circles working on its development, but ADSL2+ will likely be the most common term used to clarify that it is in fact an extension of ADSL2 and not the first ADSL standard.
So actually it's pretty damn big -- except as has been pointed out earlier, adoption isn't likely to be that fast. I expect it to start as a premium business package.
Let's call the existing distance (not specified in the article), "r". So the original and new coverage areas ought to be (in terms of feet):
orig_coverage = pi * r * r
new_coverage = pi * (r + 600) * (r + 600)
The difference between these is claimed to be 2.5 square miles. Since there's 5280 feet in a mile, the difference between these two is supposed to be:
new_coverage - orig_coverage = 2.5 * 5280 * 5280
So, putting these together, and multiplying out the (r+600)*(r+600) part, it ought to be possible to deduce the original radius: ....adding some parens to make it easier to read
(pi * r * r) + (pi * 2 * 600 * r) + (pi * 600 * 600) - (pi * r * r) = 2.5 * 5280 * 5280
So, luckily the r squared terms subtract each other out, so this little bit of math won't requiring using a quadratic equation. Subracting the constant, it turns into:
pi * 2 * 600 * r = 2.5 * 5280 * 5280 - pi * 600 * 600
Now for anyone reading this far who's good at basic algerba, I'm going to appologize for yet a couple more simple steps spelled out....
r * 3769.9 = 69696000 - 1130972.4
r = 68565027.6 / 3769.9
r = 18187.5
So it looks like existing DSL goes 3.44 miles, and this new one goes 3.56 miles, and the increase from 37.276 square mile to 39.776 square miles really is 6% (actually 6.7%).
So it does really work out, and the existing DSL distance of 3.44 miles sounds reasonable.
Of course, it's all a moot point if the FCC allows the cable and baby bells to lock out competition. The only reason almost anyone has DSL within a 3.44 mile radius is because AT&T started rolling out high speed cable. What this new DSL _really_ needs (other than a real increase in distance) is a competing technology/business and a regulatory environment that allows that competition instead of squashing it. How likely is that? Too bad there's no easy formulas there.....
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Speaking as one of those in the UK sitting pretty much on the wrong side of the limit of the 5.5km restriction we have on British Telecom's ADSL implementation, the range increase may be more promising.
I'll hit the maths a bit -
Asssuming all the lines radiate directly out of the exchange so you can assume the range limit proscribes a circle with the exchange at the center (you can tell I'm a physicist can't you?)
The range increase talked about in the UK is 5.5km -> 6km of cable length. Now compare the areas of these 2 circles.
5.5 x 5.5 x 3.14 = 95 km squared (approx)
6.0 x 6.0 x 3.14 = 113 km squared (approx)
So this gives an extra 18 km squared coverage. If we assume one household per 100 metres squared (not unreasonable in the UK) then this bring 1800 homes in range of broadband.
Of course in the real world things will vary, but I've seen figures from BT suggesting 6km will bring 97% coverage of the population.
The irony for me is I live 30 miles from London, 4 miles from the end of the runway of one of our major airports, 3 miles from one of the major motorways and yet my broadband options are the same as someone on a remote island, no ADSL, no cable, just my trusty 56k jalopy...
This is going to be a bit long but bear with me, I hope I can explain it a little.
The fundamental limit of high bandwidth technologies is due to the physical nature of copper wire.
Any digital signal is essentially a composition of a series of sine waves. Don't worry if this doesn't make sense - what happens is that the sharp 'edges' of a digital pulse are effectively very high frequency. So although it is conventient to think of a digital signal having a single frequency that is effectively the data rate, its not actually true.
One of the properties of copper wire is that different frequencies travel at different speeds in the wire, and get attenuated (lose power) at different rates.
Now we combine these two thoughts and what happens is that the well defined pulse get smeared as the frequencies that make them up seperate as the pulse goes down the line, and misshaped as attenuation kicks in. At some point this smearing will make it impossible to reconstruct the pulse. Also every single joint in the cable causes reflection of the siganl to some point.
In a transmission system this is not a problem, as the great thing with a digital signal is we know it only has two states - 1 or 0 - so we can regenerate and clean up the signal and transmit it again. This is what repeaters in undersea cables do (even fibre has to have these, but at much greater lengths than copper). But to your house there is no point in the cable to put a repeater - if the signal can be read when it gets to where you are then it works, if not then it doesn't.
Now in reality digital signals are not transmitted as a single stream of on/off pulses, but encoding systems are used that turn the signals into ranges of tones - which is why when you listen to you modem you here a range of tones, rather than a single one.
All of these techniques aim to minimise the effect of the smearing due to the different speeds the different frequencies travel, and to make the signal more resiliant to noise issues. But at some point either the pulses will become so corrupted they cannot be recognised, or the signal to noise ratio will get so bad that they can't be distinguished from noise.
Generally the problems get worse as the frequency goes up, and in data terms this is roughly the same as baud rate. This is why faster DSL rates are only available nearer the exchnage.
The reasons why ADSL2 isnt a great improvement is we are hitting fundamental limitations of copper wire transmission systems as used for analogue telephones (and it is analogue in the local loop no matter what the exchnage is) and tweaking the encoding techniques is not bringing great increases.
Remember with normal modems we hit the limit at 36Kbaud due to the fact that normal voice is limited to 0-4Khz - a bit of clever engineering managed to boost this to 56Kbaud on the downlink because you avoid one of the anti aliasing filters in the exchange.
So modems are limited to 4Khz and Shannons Law tells us the maximum data rate we can do at 4Khz, and 56Kbaud modems are damn near the limit.
ADSL is carried as a piggy back signal on your analogue line - below 4khz is the normal voice signal, above 25Khz is the ADSL signals. There is no 'hard' upper limit to ADSL due to filters like there is for voice, but there is a 'soft' limit where the problems discussed above mean its not possible to get reliable transmission.
Current ADSL is pretty close to those 'soft' limits - ADSL2 tweaks it a bit to get more in and increase the range.
The bad news is its not going to get much better on copper wire - the modem limit was due to filtering, but ADSL is down to basic physics.
Explanation of the local loop technologies - mostly found via ADSLGuide (These guys do a great job of keeping on top of UK ADSL issues)
The Last Mile - personal site, but a good heads up. Significantly shows the bandwidth limits as related to the type of wire the signal is transmitted down.
The Trouble With DSL great well written article that summarises some of the technical and practical issues with DSL.
ADSL Techincal Summary
DSL Source Book - PDF (registration required) - very good for technical geeks.
Ahh, just tweak the OS's timeout parameter. Still, the point is that it's completely ludicrous that I have to do this for a cable modem when it's never been required for POTS 56k modems.
"would imagine that telcos will start doing more of what they did for my neighborhood - install a box (looks like a large refridgerator on its side) that essentially functions as a mini Central Office. So even though we're 20,000 feet from the actual CO, we get DSL connections that are under 2,000 feet."
Your exactly right. I live out in what people would call the boonies. Cows, chickens and goats are my neighbors and I am waked up by howling dogs and roosters. However, I get very fast and reliable dsl access. I've had 1.5mb/s down and 256kbs up for a year now at $45 a month courtesy of my baby bell. It has only gone down 4x in the course of the year that I have had it, which is better than I can say about the dialup i used to have. I wish the bandwidth were higher, but I can't complain, because I don't get capped like so many cable users do. I live in an unencorporated town that is about 15 miles outside of Atlanta. They have one of those boxes not far from me, and the tech who had to repair my dsl told me that their little foray is doing well, we have 40 users on our Dslam. By extending the reach of DSL, they are able to capture the upper middle class market who live in the suburbs. Hopefully, your local telco will experiment in your area in a similar manner.
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