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."

Comments

Doesn't look too promising

[nekdut]

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.

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/siliconartic le.asp?ID=5435
http://www.dslprime.com/a/adsl21.pdf(sorry about the pdf)

Clueless commenters and meaningless links

[hoegg]

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.

Small range increases mean BIGGER area increases

[Lupulack]

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.

Though...

[cybercomm]

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.)

The real source article

[Animats]

The article is a rehash of this white paper from AWARE.

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.

Doing the math....

[pjrc]

The article says that the distance is increased by 600 feet, which translates into an additional coverage of 2.5 square miles, which is a 6% increase over the existing coverage. I'm having a hard time envisioning that, so I decided to do a bit a math, as a quick sanity check.

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.....

Range increase may be more promising.

[CharlieO]

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...