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[holmbase]

I'm on a 21st Century exchange but the service since BT upgraded the exchange in August has been pretty poor. I've tried multiple routers and stuff (see my other post) but it's quite possible that my long line (53db) coupled with Milton Keynes lovely aluminium cabling is mutually exclusive with ADSL2+.

Now my ISP gives me the option of going back to ADSL1 and I have seen that option referred to in other posts and on other sites.

What exactly does that mean and could it help with my now unstable connection? If I connected at around 3,400kbps before the 21CN upgrade with little or no line loss or down time, is that what I'll get if I 'downgrade' to ADSL1?  Is there any risk with downgrading?

Thanks

John

[roseway]

With an attenuation of 53 dB there's little or no speed advantage for you in ADSL2+, and there do seem to be a lot of problems with it at present. So my inclination would be to downgrade, but I've no personal experience in this area.

[kitz]

>> If I connected at around 3,400kbps before the 21CN upgrade with little or no line loss or down time, is that what I'll get if I 'downgrade' to ADSL1?

What did you get before? 

It does appear to be true though that once a line approaches around the 55dB atten mark, then little improvement will be seen.
Theoretically adsl2+ may give you a tiny bit of additional speed because it only needs to load a minimum of 1 bit per bin, but ultimately it depends on the overall bitloading because thats still only around 4kbps for those bins that have low SNRM.

adsl2+ also uses a broader range of frequencies, and will likely increase the overall attenuation on your line at the higher frequencies.
adsl2+ with BTw also seems to have its share of teething problems at the mo..   so if your line was much more stable on adsl1, and you are being offered to go back on it.. then yes it is a solution for many whose lines are over 50dB.

[holmbase]

I have today downgraded to ADSL 8mbs so we shall see from tomorrow whether that provides a more reliable line. I shall post feedback later in the week.

On a related note.

BE are also in my exchange (indeed my ISP is now offering services via a BE connection albeit with a £20+ per month premium). Does BE use something like DLM and is it any more tolerant of noisy lines than BT? Or put another way, what are the chances of me getting a better ADSL2+ connection with BE than with BT if the only real difference is the kit in the exchange?

Thanks

[kitz]

Good luck with it


---

BE have their own DLM, but its nothing like the BTw one.  Theres no IP profile, and their users have a control panel where youre able to set some of the line features yourself...  such as interleaving and target SNR.
Plus theyve been doing adsl2+ for many years and dont seem to have any where near the amount of problems with it that BT are having right now.

However the technology behind it is the same, so adsl2+ wont really give you that much (if anymore) speed than adsl1.
It wouldnt be worth while you paying for the up to 24Mb as your line wouldnt be able to cope.  Be Value (up to 8Mb) should be fine.

Be aware though that sometime BE are a bit tetchy about taking on some longer lines, simply because they know that they can be more problematic.
They do seem to have relaxed this rule a bit of late though.

[holmbase]

Okay. It's still slightly early days but the line is now back to roughly where it was before. I was changed back to ADSL 8mbs last Wednesday. I'm currently using a voyager 220v router as the 2700hgv didn't seem to like the ADSL2+ line and the ST546 seemed a bit unhappy.

Today I'm syncing at 3,936kbps with an snr of 15db. I just miss out on the 3.5M bras so I'm currently at 3.0M. [That annoys me: why cut my actual speed to 75% of the headline speed?]  Errors don't seem too bad and reconnects have virtually stopped once I moved up from the default snr of 6db.

Before the 21CN debacle, I was syncing at 3,402kbps with a bras of 2.5M and (I think) snr of 18db - it might have been 15db.

So I seem to be back where I was - hurray, of sorts!!

What is interesting is what has happened upstream. On ADSL2+, all dlm did was to increase my downstream snr: my upstream snr stayed at 6db, often falling lower. So by the end, my downstream snr was 24db (sync at 1,492kbps)but my upstream was 4.5db (about 1,000kbps). And upstream I had shedloads of errors of all kinds.

Now on 8mbs my upstream snr is about 12 db, the sync rate is 832kbps and I have no errors - none.

So I'm wondering whether part (but only part) of my problem was the errors associated with upstream activity. Is this possible? Why doesn't dlm increase upstream snr/decrease upstream snyc rate - only downstream??

My only hope now is that:
a) the aluminium rubbish is from cab-exchange NOT cab-house
b) my exchange is on the FTTC roll out at some point

otherwise I fear I'm stuck with these speeds (which are admittedly better than some) until some form of wireless or affective 3g comes to my area.

John

[roseway]

With ADSL Max the upstream connection speed is limited to 448 kbps on domestic accounts, and 832 kbps on business accounts. The upstream noise margin isn't directly controlled by DLM, but will settle at whatever value it gets for the required upstream speed. But with BT ADSL2+ the upstream speed is negotiated at connection time in the same way as for the downstream speed, with a target noise margin of 6 dB.