If your router is unable to maintain a constant connection with the broadband equipment in your local exchange you may suffer from intermittent disconnections.
This particular fault is often the result of either:
- Incorrect physical set up (wiring and filtering)
- A line fault (including high noise levels)
- Equipment failure (router/filter)
- Outside interference
Common causes of disconnections
Interference is a very common cause of disconnection. You will see your connection drop, and then reconnect after a short period of time. This is of course extremely frustrating for users who are attempting to browse the Internet or are in the middle of a VoIP call.
- Repetitive Electrical Impulse Noise (REIN): where interference is generated the whole time that a device is on, potentially causing slow speeds, frequent disconnections or even preventing you connecting to the Internet at all
- Single Isolated Impulse Noise (SHINE): in this case the interference is generated as a burst, for example when the device powers on or off. You may spot a disconnection at these times that correlates to the device powering on or off
- Halogen lamps
- Fluorescent lights
- 900 MHz cordless phones
- Some mobile phones
- AM or home built radios
- Dial up modem, fax, or other non standard device on the telephone line
- Microwave ovens
- Broadband modems connected to telephone extension cables
- House security/Alarm system
- The PC or peripheral devices (scanners, external drives etc.) if the modem is located on top of or directly beside these devices
- Central heating thermostats
- Christmas tree lights (yes really!)
With this particular issue it is important to note if you actually lose the broadband signal when the connection drops, the loss of the broadband signal is indicated by a flashing or completely absent DSL light on the router.
It's also worth trying to see if there is any pattern to the connection dropping, such as occurring at a particular time of day, the frequency and the duration or anything that you are doing at the time (like sending a fax), as these may help identify the cause of the issues. Disconnections caused by SHINE will often occur at regular points in the day, whereas disconnections caused by REIN will often occur when you start using a device.
If you get intermittently disconnected but your DSL light remains solid then it's just the connection between your PC and the router that is dropping and not the broadband connection.
Advanced configuration and troubleshooting
There are other checks and tests you can carry out.
Test that your phone line is working OK by checking for a dial tone. If your phone does not have a dial tone this indicates a telephony problem which should be reported to BT directly on 151. Interference may be caused if you use cordless phones so make sure that the cordless' base unit is connected via a DSL filter also.
Check the connection sequence for your modem:
- Your modem should connect to an DSL filter
- This filter should connect directly to your phone socket ensuring there are no splitters on the telephone socket. More information on filter setup is available in the getting started section of the knowledge base
Where possible you should always avoid using a phone extension cable to connect to your router. Most telephone extension leads are not capable of caring the higher and lower signals used by Broadband.
Note: It is important that all phone devices in your property are connected via filters. This includes equipment such as cordless phone base unit, satellite digibox, fax machine and some alarm systems.
The only exception to this is if you are on a Fibre To The Cabinet Service and have a telephone socket that has separate DSL and telephone sockets.
To test for interference, first remove all other devices connected to the phone line in your property so that your router is the only device connected to the phone line via a DSL filter.If this does not resolve the problem then switch the DSL filter in use with another filter to ensure the filter is not faulty.
If it still doesn't work connect the router to the main BT socket.
(The main BT socket is the point where the telephone line enters the building) to check if that works.
In some cases the cause may be outside your property. It could be the premises next door or something next to the phone line at any point between your premises and the exchange. If this is the case other users are likely to have a similar problems. If you try to log as much as information about the disconnections (time of day, frequency, length of disconnection) as possible it will make it easier for Openreach to cross-reference faults and hopefully identify the cause.
Line (Downstream) Attenuation
This describes the loss of your broadband signal over distance. The greater your distance from your local telephone exchange, the weaker your received signal is likely to be. If the quality of the telephone cable is poor, this can also increase attenuation.
- 75 dB+ Out of range for broadband
- 60-75 dB up to 512kbps
- 43-60dB up to 1Mbps (higher speeds with MaxDSL)
- 0-42dB up to 2Mbps+ (higher speeds with MaxDSL)
A dB (Decibel) is a measure of sound intensity. It's a logarithmic unit, so an increase in 3dB is equal to double your original intensity.
SNR (Signal to Noise Ratio)
This is a bit like television reception. A high SNR means you're getting a good clean signal with no static or interference. A low SNR and broadband signal is being drowned out by noise. Watching a bad TV picture may be annoying, but you can still use your TV. With your broadband, lots of noise can quickly lead to a complete loss of your connection. SNR is not usually provided as a line stat, most hardware will show SNR Margin instead.
SNR Margin (or Noise Margin)
This is a measure of the difference between your current SNR and the SNR that is required to keep a reliable service at your connection speed. If your SNR is very close to the minimum required SNR, you are more likely to suffer intermittent connection faults, or slowdowns. You need a high margin to ensure that bursts of interference don't cause constant disconnections.