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Connection Problems

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A list of some of the most common adsl faults & problems and how to identifiy them together with possible solutions.


~ Crackling noise on the telephone line.

Crackling noises/static on the line when using the telephone is indicative of incorrectly fitted filters.

  • Make sure that you have installed all your filters correctly (see here).
  • It is important that each telephone device has a filter fitted. Don't forget fax machines and sky boxes also need a filter.

~ adsl drops out when phone call is made or received.

  • Incorrectly installed filters - check filters are installed correctly see here.
  • Faulty filters - replace one by one to identify which filter is faulty.
  • Fault on the line - unlikely but possible if all else has been eliminated.

~ adsl only works when the phone is being used.

  • Check filters and internal wiring.
  • Check for noise on the line which may help identify the problem by doing a "quiet line test".
    (Dial 17070 and select option 2).
  • If so - Possibly a fault on the actual phone line perhaps due to worn cables or water on the line.
    There may be times when a cable or joint is only slightly damaged/corroded and shows no immediate problem, however the damage is sufficient to increase resistance on the line.
    When the phone line is in use, it generates a small electrical current which is needed to carry the voice signal. This current helps reduce resistance on the line and can be sufficient to "bridge the gap" just enough to carry the adsl signal. This is known as a High Open or High Resistance Fault.

  • LLU lines could try dialling the number 020 8759 9036 for a Quiet Line Test.

~ adsl disconnects when the phone rings.

  • Check filters and internal wiring.
  • Check for noise on the line by doing a quiet line test. - Dial 17070 and select option 2.
  • You can also use BTs Ring Back Facility to test - Dial 17070  and select option 1. 
    If your telephone number is withheld use 1470 before dialling 17070
  • Possibly a fault on the actual phone line perhaps due to worn cables or water on the line.
    Uncommon problem but possibly related to high resistance on the line caused by a worn cable/damaged joint.

~ Slow Speeds.

Various factors can cause slow download speeds.

  • Check out my slow speeds page for more information and fault finding tips if you have slow speeds.

~ No sync.

If your modem/router cant synchronise with the exchange (as indicated by a flashing green "adsl" light).

  • ADSL adsl not active.
  • Incorrectly installed filters.
  • Problem with the local line.

~ Dropped connections.

Could be a few things:-

  • ISP Problems - Check your ISP Service status records - are they doing any "load balancing".
  • USB Modem - USB Modem problems are not uncommon, particularly with older PC's and unpowered usb hubs - see below.
  • Maximum IP Sessions - Most routers have a limit on the number of IP sessions it can maintain. If this limit is reached then some "older" connection sessions may be dropped. Check the maxIP session limit on your router and adjust if necessary. - Instructions for the SAR110 and Voyager 205 here.
  • Low SNR problems. Fairly common particularly if you are on a long line and are on a rate adaptive "Up to 8Mb" type connection.

~ Frequent Dropped Connections / Loss of sync.

Not so very long ago this was a fairly rare event. However many users have recently been upgraded to 2Mb and higher speeds and soon after found that their connections routinely drop, particularly in the evenings.

  • This problem is now so common place that I have dedicated a page to this particular problem which is caused by low SNR.

~ I Cant view some web sites

This problem usually affects hotmail, ebay and microsoft sites.

  • Try setting your MTU to a lower figure. More information on MTU issues.
  • Perform a tracert to see if there's a problem with routing.

~ No Dial Tone

Telephone lines consist of 2 wires - Power and Earth. If the circuit is not completed dial tone cannot be achieved.

  • DIS - Line is broken at some point. Identified by no capacitance reading at the NTE5.
  • LOOP - Line has short circuit caused by the 2 wires touching somewhere.

~ Noisy Line

Identified from the Quiet Line Test (Dial 17070 and select option 2). Possible causes:-

  • HR Fault - One or both wires not making proper contact. Worn cable or oxidised joint.
  • Earth Contact - Line is going to earth, possibly caused by tree branch rubbing through the cable.
  • Battery Contact - Line is in contact with another. Could be worn isolation or water on the line.
  • Rectified Loop - Phone rings once then line cuts out. Problem could be in the home or water on the circuit.

~ Unexplained increase in Attenuation

  • An unexplained increase in attenuation may be faulty internal wiring or a line fault, such as caused by corrosion on a joint.
  • An RF filter on the line is a possible explanation if the attenuation is much higher than anticipated.

~ USB Modem Problems.

USB Modems can cause a lot of connection problems for some users, particularly those with older PCs.

The first thing to check would be ensure that you have the latest drivers for your usb modem which you can download from the manufacturers site. Its very important to make sure you install the drivers before connecting the modem up to your PC.

Some motherboards* and older Operating Systems** simply do not bode well with USB modems at all, and the solution in cases such as these would be to consider connecting via ethernet or a PCI adsl modem.

One of the most common issues is that the usb modem simply draws too much power from your PC. In cases such as this you should either consider buying a powered usb hub or connecting via ethernet.

USB modems can drain a lot of power from your PC, for this reason alone I much prefer a router which has its own power supply, processor and memory. The router takes over total control of your internet connection allowing your PC to get on with what you want it to do.

Most modems require 500mA of power and most modern PCs can supply a full 500mA on each USB port.

However it's worth noting that this isn't always the case, particularly on some older or cheaper PCs*. On such PCs the power available for all USB ports is limited to just 500mA in total, which can present problems if you have more than one USB device connected.

For example, you may find that your modem works until you plug a scanner in, which causes the modem to drop out, simply because there may not be sufficient power to drive both devices at the same time. This can be solved by purchasing a powered USB hub, which uses mains power rather than drawing it from the PC.

* Motherboards using Intel chipsets are usually fine. Please note that an Intel chipset is NOT the same as an Intel processor.
** Windows 95, NT and Windows 98 (first edition).

Its also worth noting that whilst the available USB bandwidth that peripherals use is limited, a USB modem will try and adapt to make use of the bandwidth that is available. Therefore if you are going to attach other USB devices such as a usb mouse or keyboard, ensure that these are plugged into the PC before hooking up the modem.
Otherwise the modem will consume a fixed bandwidth and the remaining bandwidth may not be sufficient for other USB devices. In cases such as this you will see an error messages stating that the the USB controller bandwidth is exceeded.

USB - Bulk mode or Isochronous mode.

USB has two different types of transfer modes:

  • Isochronous - Reserves the amount of bandwidth that the device requires
  • Bulk - Uses what bandwidth is available.

USB modems that operate in Bulk mode can sometimes see slower speeds due to modem being unable to match the USB and DSL rate (USB1 only has 11 Mbps available bandwidth for all devices attached) and the effects are slow speeds due to insufficient available bandwidth on the USB channel.

Switching to isochronous mode may provide a solution.

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