Troubleshooting Line Quality Issues
If speed test numbers show that you aren't getting the broadband speed you should, you may be experiencing problems due to line quality issues. You need to check your modem’s web interface to see if it is reporting that you are experiencing poor signal quality. This is usually report as a signal-to-noise ratio.
Login to your modem’s interface and have a look at the signal-to-noise ratio (or SN margin) and line attenuation numbers, both are measured in decibels (dB). The lower the signal-to-noise ratio, the more interference there is on the line. As a result, there will be a greater number of packets that will become lost or corrupt during transmission process and therefore will need to be re-sent. This causes your Internet connection to work less efficiently because it has to redo some work it had done before. For this reason, a noisy line can dramatically reduce your bandwidth.
While you are checking the SN margin/ratio, you may want to have a look at the line attenuation number as well. Line attenuation measures the drop in voltage that is realized as the data signals travel through the data medium (phone line, or cable). In essence, this is the strength of the signal that is received by the modem; it's measured in dB. For DSL modems, any line attenuation number above 50 dB is poor, and 20 to 30 dB is excellent. For signal-to-noise ratio, 7 to 10 dB is marginal, and 20 to 28 dB is excellent. Please note, what is considered acceptable may vary among ISPs, so don’t bulldog the technical support guy if he seems nonchalant about the bad SN margins and line attenuation numbers you are experiencing.
If your numbers aren't good, you may need to verify that the wiring on your premises isn’t at fault. To check that the fault is not in your wiring, change or swap the cable that runs between the wall jack and your network equipment. It is also a good idea to have an electrician check that all you outlets are properly grounded and that your power cords and data cables are properly shielded. You may experience data transmission problems due to interference from power supply faults on nearby equipment. If the problem persists, after you have verified that there is no fault on your premises, you may need to ask your ISP to resolve the problem from their end.
If you have DSL service, check that DSL/POT splitters are properly installed on the telephone line. DSL splitters are designed to separate the data and voice signals that are transmitted on the phone line, that is being used for the DSL service. For your DSL service to work properly, a filter has to be placed between the wall jack and each network device that uses the Internet connection. If this device is not installed properly, not only will you experience reduced speeds, but your will also hear static in the line when you make phone calls.