Knowledgebase
ADSL2/2+ Tips and hints
Posted by Gabriel Yu on 14 March 2008 04:32 AM

Because ADSL2 (max 12Mbps) and ADSL2+ (24Mbps) operate at much higher speeds, they are more prone to interference and noise on the phone line than ADSL1. Unfortunately debugging ADSL2/2+ synchronisation and drop-out problems is very much an arcane art, consisting of “try this” until either the problem is resolved, everyone runs out of ideas, or the user accepts that its as good as it gets.

The key indicators of ADSL2 performance are SNR Margin and Loop Attenuation, and you can find these in the bottom right corner of the Online Status page.

  • Loop Attenuation can be used as a rough gauge of distance from your telephone exchange (13.81 per kilometre), and so the lower the better. See What ADSL2/2+ speed am I likely to get ?
  • SNR (Signal to Noise Ratio) indicates how clearly your modem can hear the ADSL signal over any background noise, and so the higher the better. Note however that Telstra has no hard limits for either of these.

This is our list of Tips:

  1. Update your modem/router’s firmware. DrayTek have supplied several “flavours” of each firmware version (see here) with different modem code. The different "Modem Code"s indicate different fine tuning settings of the ADSL2 parameters - so some will be better and some worse on any individual phone line. ALL the modem codes on our download page will work in Australia/New Zealand. Test each in turn until you (a) get an acceptable connection, or (b) determine the “best” firmware for your combination of ISP, DSLAM and phone line.
  2. ADSL2 filter – a standard ADSL filter is not good enough ! You need an ADSL2 filter which complies with the new Australian Standard AS/ACIFS041:2005. Note that RCIT.0004 is the OLD ADSL1 standard, and some of the cheaper filters actually create interference on the line.
  3. Often the problem is within your premesis, so perform an Isolation test.
    1. Unplug all phones, fax machines, modems, etc. from the phone line used for your ADSL connection. Now plug in ONLY the ADSL modem and test the connection. Check the SNR Margin, Loop Attenuation, Up and Down speeds; as descrived in How can I know if I have a good connection ?.
    2. If there is a difference between these values and your normal values, then connect one other phone device to the phone line, and check the SNR etc.
    3. Do the same for each phone device you have. This should indicate which (if any) device is causing a problem.
    4. Note that loose cables and faulty connections can also cause problems, as can faulty ADSL filters – so you might like to try different combinations of device / extension socket / cable to determine which of these is the culprit.
  4. Try a friend’s modem on your ADSL line, or try your modem on their ADSL line. This should help to indicate whether the fault is with the modem or the ADSL phone line.

OK, tried all that, but I still have a problem. What next ?

  1. Document the steps above which you have tried, with the results. This will save a lot of time for both you and the support technicians.
  2. Email this documentation along with model and firmware version to support@draytek.com.au

 

Finally, after you have determined your speed, we recommend documenting your current settings and values as a reference point. Screen dumps of Online Status and other relevant web configurator pages, pasted into a Word or Wordpad document is easy and worthwhile. If you want, you can also use the Vigor's telnet interface to document the various adsl settings, and Mark and Paste this into the document.

Why do this ? Because things can and do change. for example, ADSL performance can errode gradually because of increased crosstalk or suddenly because your copper pair was swapped. The fact is that Telstra, ISPs, etc don't tell you about every change which might affect you (e.g. telephone exchange upgrades, DSLAM firmware upgrades, swapping copper pairs in your street), and they hope that the change won't affect you enough to make you complain. From your end, it is a lot easier to get your problem fixed (or at least reduced) if you can produce objective evidence (e.g. that your Loop Attenuation was 18.5 on 3rd March, and now it's 65).

Be aware also that your ISP could simply take the attitude that as long as you get 1.5M/256K speed then you have nothing to complain about because their ADSL2+ plan is priced the same as 1500/256.

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