21CN: any improvement onstability for long/sub-prime lines

techguy · ‎12-09-2008

Hi
I'm started this thread so that I don't incur the wrath of PN staff/mods as I'm not likely to be a trial candidate.
Jamesh is currently looking to see if we can get my line stable as its up and down (as its long and sub-prime) so hats off to him for that.
It looks as though the emphasis is upping the speed again which is great of course (though still a long way from the 100 meg I enjoy at work

However there does not seem to be any tweaks to improve stability or is there something I've missed?

MauriceC · ‎10-04-2007

The simple answer is probably not. 21CN and the technology it uses is good at squeezing the last bit of performance out of a good copper pair. But you have to realise that this technology is very close (if not already at!) the practical limits for such wiring. As distance increases, so does the attenuation and susceptibility to induced 'noise' - this in turn limits the frequencies that can reliably be used to support ADSL.
So what next? Undoubtedly, as with current routers, there will be enhancements to what can be achieved - but I have to say that there seems limited optimism in the industry for any significant change. Other technologies are being worked on, but fibre deployment does seem to be the next logical step - and it ain't cheap.

Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.

techguy · ‎12-09-2008

Yeah true
All of the buildings where I work are linked with fibre for that reason.

James · ‎04-04-2007

Kinda, but not really.
DLM is being improved to be more intelligent, so the changes in IP Profile should be worked out more "intelligently" and faster, so whilst there won't be an improvement in stability as such, the speed at which changes occur should be improved.

techguy · ‎12-09-2008

Wish they'd figure out a way to amp the signal a little more as suure that'd do it.

MauriceC · ‎10-04-2007

I'm sure the IEEE would welcome your input to the next generation of the specification

Maurice

Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.

techguy · ‎12-09-2008

I did GCSE electronics but thats about it.

so wouldn't know where to start.
I just want them to hurry up with fibre and maybe Ethernet from a street cabinet to the home.

VileReynard · ‎01-09-2007

Since ADSL2 uses twice the bandwidth of ADSL it seems reasonable to expect a teensy extra bit or two of data rate?

"In The Beginning Was The Word, And The Word Was Aardvark."

zubel · ‎08-06-2007

The ADSL2+ specification allows for *downstream* data bits to be transmitted in the 0.14MHz - 2.2MHz band., whereas ADSL allows for downstream transmission to occur in the 0.14MHz - 1.1MHz band.
So, you're using twice the number of frequencies to transfer (up to) 3x the amount of data that ADSL does. That's why ADSL2+ is much more susceptible to interference and attenuation losses that ADSL is.
That being said, I suspect that natural improvements in technology will make the available bandwidth on ADSL2+ generally higher than ADSL even on "slightly more dodgy" lines eventually.
B.

Oldjim · ‎15-06-2007

Deleted - as I didn't read the post properly

techguy · ‎12-09-2008

I was on O2 for a month which is of course ADSL2+ and kept having frequent resynchs which would stop downloads and cause frequent not found errors in the browser.
Was a right pain.

avatastic · ‎30-07-2007

Quote from: Barry
The ADSL2+ specification allows for *downstream* data bits to be transmitted in the 0.14MHz - 2.2MHz band., whereas ADSL allows for downstream transmission to occur in the 0.14MHz - 1.1MHz band.

I don't suppose that anyone is technically mind enough, and has read the spec, to know if sub-optimal lines will pick the best frequencies in the new range for stability rather than throughput?
i.e. If you can't get a stable line on ADSL 1 due to interference, solar flares, etc, will the new standard attempt to just operate in the newly available 1.2-2.2 band, or does the spec require that the full frequency range is used?
Just some pre-work, pre-caffine assimilation ramblings.
A.
ps. if no-one has thought of that, i call patentsies on the idea!

F9 member since 4 Sep 1999
F9 ADSL customer since 27 Aug 2004
DLM manages your line the same way DRM manages your rights.
Look at all the pretty graphs! (now with uptime logging!)

zubel · ‎08-06-2007

With standard ADSL2+ , the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz – 2208 kHz is used for downstream communication. Each of these is further divided into smaller frequency channels of 4.3125 kHz. During initial training, the ADSL modem tests which of the available channels have an acceptable signal-to-noise ratio. The distance from the telephone exchange, noise on the copper wire, or interference from AM radio stations may introduce errors on some frequencies. By keeping the channels small, a high error rate on one frequency need not render the line unusable: the individual channel will not be used, resulting in reduced throughput on an otherwise functional ADSL connection.
The only critical frequency is the ADSL pilot tone, which nominally sits around 280 kHz. This acts as a communication frequency that the CPE equipment and the DSLAM use to negotiate sync changes without dropping the connection (amongst other things). If there is any REIN or interference around this tone then it is unlikely that ADSL equipment will function at all (let alone ADSL2+).
So, if you have a line that is currently unstable, then ADSL2+ *may* benefit you as it is perfectly feasible for it to use just the >1108kHz frequencies - as long as the pilot tone survives.
B.

avatastic · ‎30-07-2007

Thanks Barry that nicely answers everything! (for me at least!)
A.

F9 member since 4 Sep 1999
F9 ADSL customer since 27 Aug 2004
DLM manages your line the same way DRM manages your rights.
Look at all the pretty graphs! (now with uptime logging!)

godsell4 · ‎06-04-2007

Quote from: darkskye

I don't suppose that anyone is technically mind enough, and has read the spec, to know if sub-optimal lines will pick the best frequencies in the new range for stability rather than throughput?

This is an inherent part of ADSL2+, it is called Seamless Rate Adaption (SRA). The line is monitored/analysed at all time to 'see' if there are channels that can be used if not already, and to stop using any channels if they have become noisy.
My speculation, for most of the daytime when noise and interference is low, your modem will give a 'Sync Speed' that is high, and from 17:00 to 05:00 the next morning the speed will be lower. Hopefully though, these changes in speed are expected to be seamless!
It could be the Be/O2 implementation, as described below had problems, and BT have something else planned but based on SRA. Only time will tell!
SW.

--
3Mb FTTC
https://portal.plus.net/my.html?action=data_transfer_speed