help with maxdsl in plain english please

have probably got the concept of maxdsl all wrong and would be grateful if
some one could explain simply in plain English (not plusnet c/s talk).

I was upgraded 2 weeks ago and have seen my data rate & snr reported by my
modem vary as i understand is the case during the training period. When my
data rate has been over 4500 snr has been low resulting in a poor connection
that is slow and disconnects.

my understanding is that after training the my data rate would not be over a
certain amount resulting in a balance between performance and stability. I
believe that this is around 4 - 4.5 mb when my modem has shown data rate of
4-4.5 things have been good. This is not the case and the data rate still
varies resulting in unreliable connection.

C/s told me that my account is set to 4 mb ! but i am confused as modem
reports a high date rate.

Can any one correct me if my understanding is wrong


thanks

adam

In message <4541d326$0$8721$(E-Mail Removed)>,
dylan30 <(E-Mail Removed)> writes
> have probably got the concept of maxdsl all wrong and would be grateful if
>some one could explain simply in plain English (not plusnet c/s talk).
>
>I was upgraded 2 weeks ago and have seen my data rate & snr reported by my
>modem vary as i understand is the case during the training period. When my
>data rate has been over 4500 snr has been low resulting in a poor connection
>that is slow and disconnects.
>
>my understanding is that after training the my data rate would not be over a
>certain amount resulting in a balance between performance and stability. I
>believe that this is around 4 - 4.5 mb when my modem has shown data rate of
>4-4.5 things have been good. This is not the case and the data rate still
>varies resulting in unreliable connection.
>
>C/s told me that my account is set to 4 mb ! but i am confused as modem
>reports a high date rate.
>
>Can any one correct me if my understanding is wrong
>
>
>thanks
>
>adam
>
>
>
>
I am not an expert, but in the plainest English I can manage.

Two separate issues

1) The rate between your ADSL modem and the DSLAM (BT or the Local Loop
providers box) in the exchange.

2) The BRAS(?) rate as reported by the exchange kit back to the ISP.

The second of these 2) is what Plusnet told you was 4Mb This is the
maximum rate at which the exchange "wants" data for your ADSL link. I
assume this is set to minimise the amount of buffering at the exchange
and/or retransmission on the backbone network and is the maximum
reliable long term data rate that the exchange kit thinks the link can
cope with. I think setting this is the main reason for the training
period.

1) is the "adaptive" part of the MAX product. This attempts to find (as
you say) the best balance between speed and stability on the flakiest
part of the link. It continuously (as far as I can tell) tries to
optimize the data rate. After 6 months the data rate on my link varies
from 5M plus down to just under 4. My BRAS is 4M.

I think the issue is that the rate adaptation scheme makes assumptions
about the signal to noise profile on the link (that it will be
reasonably constant?). Where a link meets the expected profile the link
speed settles down to some value and the BRAS rate is reported as just
below this.

However if a link has an untypical noise profile (e.g. the line passes
close to an intermittent source of external interference) then for
fairly long periods the exchange sees a signal to noise ratio that
suggests the link will support a higher data rate - so it adapts
upwards. Then the source of interference kicks in, s/n ratio dips below
acceptable and you get line drops - and the rate adapts down again. The
external source stops, and the cycle begins again.

I believe there are ADSL modems that can be told the maximum data rate
at which they should negotiate sync with the exchange, presumably this
was included in the ADSL spec to allow for such abnormal noise profiles.
Judicious use of Google should find you details.

My link drops out once or twice a day for these reasons (I think). I
just live with it as the price of generally higher speeds from the
adaptive system than I could ever get from a fixed speed link. But
then I am not a gamer!

I assume that BT don't want to lock the link rate adaption down too much
so that they can automatically give users the advantage of improvements
in the link performance (e.g. if you get a new, better performing,
modem). I believe that the BRAS rate changes if the link speed improves
for a long (days) period.

Hope this helps. OTOH someone may come along and put me right!


--
Peter R Cook

thanks peter i will read that again and again and some of it will sink
in. maxdsl is a very technical product and i feel it is not quite
consumer friendly. With some isp's being far from user friendly it's can
create big problems.

thanks again
adam

"Peter R Cook" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> My link drops out once or twice a day for these reasons (I think). I just
> live with it as the price of generally higher speeds from the adaptive
> system than I could ever get from a fixed speed link. But then I am not
> a gamer!

Me too, and my sentiments exactly!

I'm currently working at 2.9Mb/s (can be anything up to 3.2), which I know
from experience will disconnect and reconnect at a lower speed some time
later today, and will end up sometime tonight at about 2.1.
However, my BT Wholesale "forecast speed" is 1.5Mb/s (long rural line) and
my stable rate is shown on my ISP's website as 1500.
If I pressed my ISP to contact BT and get them to tweak my connection so
that it didn't disconnect/reconnect, I suspect strongly that my new stable
connection might end up at 1.5Mb/s or slower.

Not being a gamer or a mega-downloader, I'm happy with the higher speed and
the occasional disconnection/reconnection.

George

In message <454321bb$0$8733$(E-Mail Removed)>,
dylan30 <(E-Mail Removed)> writes
>thanks peter i will read that again and again and some of it will sink
>in. maxdsl is a very technical product and i feel it is not quite
>consumer friendly. With some isp's being far from user friendly it's
>can create big problems.
>
>thanks again
>adam
My pleasure, until I wrote it I must confess I had not really thought
about the complexity of the issues involved, and figured out the reason
for having a BRAS rate ( I may be wrong).

MAXdsl is a very sophisticated system (I come from the days of when
mobile computing was a DOS based laptop with a separate 300bps modem)
and must be operating very very close to the limits of the currently
possible (the speeds achieved over the installed copper infrastructure -
not the absolute speed, with fibre all sorts are possible).

By consumer friendly, I assume you mean simple to use, reliable, and
"does what it says on the can" for 99.9999% of customers.

I agree MAXdsl is not that. To make it like that would (I suspect)
require BT (and the modem makers?) to turn down the optimisation
algorithms - and lots of people (90%+) would not get the benefits of the
speed that is possible. Turn up the aggression of the optimisation and
the majority of customers see an improvement, but a minority (1%?) see
increased problems. Its a complex call about where to set the "knob",
not made easier because they probably had to make it when specifying the
system without too much practical experience, and because "ideal"
behaviour varies from consumer to consumer. Gamers want low pings (turn
off interleaving which aids stability) and high link reliability - and
most would sacrifice some speed for that. Downloaders want total
throughput (occasional dropouts are recoverable by the application) ping
times can be fairly high. Browsers want high speed (for responsiveness)
but few link dropouts etc. etc. etc.

One way to solve the problem would be to offer additional tuning
controls to the users, but consumer history says that controls that are
useful to the informed minority at the margin simply get a significant
proportion of the majority into more trouble, drive up call rates and
reduce user satisfaction (why do you think most large companies
"lock-down" windows on their desktops - its not just to be awkward? Why
do TV makers spend money to make their boxes "self-tune"?)

BT tread a fine line - they don't get it all right, but given the
complexity of what they are trying to do, I think they do fairly well.

Good luck with your MAX link. Research the issue, understand the options
and select and ISP and a modem that allow you to use the system the way
you want to.

Regards
--
Peter R Cook