Date   : Thu, 06 May 2010 15:20:12 +0100
From   : adsb@... (Andrew Benham)
Subject: [OT] ADSL capabilities

On 05/05/10 20:14, Andrew Hancock wrote:

> 'bits per frequency bin' data on your ADSL modem ? you'd have to explain
> this.

I know you've already posted some graphs, but "for the tape" a good
explanation is at   http://www.kitz.co.uk/adsl/adsl_technology.htm

The ADSL signal on the line is split into ~4.3kHz radio channels
(conventionally called 'bins'), and then the signal-to-noise ratio
on each channel is measured to see whether that channel is usable and
if so how many bits of data can be carried on it.
If you live next door to the exchange then you might be able to
carry 15 bits of data on all 223 downstream channels.  As you
move further from the exchange so the higher frequency channels become
progressively less usable, and noise reduces the number of bits that
can be carried on other channels.
Which is all fine and dandy, but normally you can't do much about what
you're getting in terms of performance.  What you can do though is to
look for holes - where a group of neighbouring channels are unusable -
this can indicate RF interference.  And if you experience problems,
it's useful to be able to see what has changed - which means that you
need to have captured the data when the ADSL was working :-)

> I doubt other users on Eclipse, one is with the Post Office and the
> Other with BT, I don't know about the other three, we'd have to survey
> them, but we are all off the same pole. They are close, metres away, as
> from the pole outside my house!

OK.  If they are all on BT Wholesale products then we can discount
different DSLAM/MSAN hardware at the exchange.  If you were still LLU'd
for ADSL then there would have been one more variable.

> What is odd, is this seems to occur, when we get cold spells, and hot
> spells, so frosts, and hot days. E.g. above average or below average
> external temperatures.

In my experience, this sounds like something slightly bad with your
pair.  I tend to lose some speed when it rains.  Often after a really
bad storm my ADSL goes bad, and the BT man comes along and pumps the
water out of the manhole/chamber by the next pole along.

[ You've no idea how hard it is for me (with my initials) to keep
  typing 'ADSL' ]

-- 
Andrew Benham         adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill"