Unfortunately ADSL2/2+ is still more of an art than a sciience, with
most suggestions being "try this..." or "try that ...". So how can you
know whether there is and improvement ?
Fortunately most of the information can be inferred from the Online Status page.
- Look at Loop Attenuation and SNR on the Online Status page. Your objective is to decrease Loop Attenuation and/or increase SNR.
- Note
the Modulation, Up Speed, and Down Speed. Periodically your modem will
“train” with the DSLAN to re-evaluate which settings and speed is
best. Sometimes this will result in your synchronisation speed (shown
as Down Speed and Up Speed on the Online Status page) going down over
time. Note that the actual data throughput could be significantly
lower than the Sync speed.
Many customers (particularly those
further from the exchange) find that G.DMT modulation (the ADSL1
standard) provides fewer dropouts and higher actual throughput, even
though the ADSL2 or ADSL2+ modulations might show a higher Sync. Speed.
- Also on the Online Status page, look at the
Connection time on the WAN Status section, Corrected Blocks and
Uncorrected blocks. You can’t be sitting in front of your modem to see
every time it drops out – but the Connection time indicates how long
ago the last drop-out was. So if your Modem’s Up Time is 200 hours but
the Connection time never gets higher than 10 hours, the ADSL must be
dropping out. However if the Modem's Up time never gets higher than 10
hours then the entire Vigor is rebooting periodically.
- Finally
on the Online Status page, look at the Corrected Blocks and Uncorrected
blocks. Occasionally there will be a bit of noise on the phone line
which corrupts the data received. If it’s a simple 1-bit error the
circuitry in the modem can work out which bit was wrong and correct
it. However more complex errors are ‘uncorrectable’ and require the
block to be re-transmitted – which is going to take longer for your
computer to receive the data. Again there’s no hard limit to what is
acceptable, but you will want the ratio of Uncorrected Blocks to RX
Blocks to be as low as possible.
After trying several firmware/filters/etc you will have several sets
of results - and probably no clear winner. Unfortunately there's no
simple answer; and you may have to trade off speed of ADSL2/2+ against
stability of ADSL1.
If you have a Vigor 2800 or Vigor 2600 model, you can look at the
Disgnostics > ADSL Spectrum Analysis graphs. The “BIN”s along the x
axis indicate the different frequencies which can carry data, and the
height of the bar indicates how many bits of data can be trannmitted at
that frequency. The red bars at the left are used for Upstream. ADSL1
uses only the first 255 BINs.
