What can be causing the tremendous amount of FEC and CRC errors via the DSL connection

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I am using Windows 7, Intel core processor, I7-4770K CPU @ 3.50 GHz, 64-bit operating system and 8 GB of RAM and for over 6 weeks I have been having intermittent disconnections — FEC and CRC errors almost daily — from the internet which prompted my calling my DSL provider.

They have come to my home several times in an attempt to resolve the issue.

They've changed several wirings, switched out the modem, checked the phone lines, monitored my PC for errors, etc. During one of their visits, they showed me a way to see the errors I was getting.

And after their "extensive" work, they finally told me yesterday that the problem was with my computer. The FEC and CRC errors can appear at any time; there seems to be no real pattern.

To give you an example, just since they left yesterday afternoon (it's been about 24 hours), I have had 5,205,160 FEC errors and 1,063,952 CRC errors. They continue to flood in as I am writing this. In the last 15 minutes, I have had 396,474 CRC errors alone.

Another weird thing is that my modem's lights are active (e.g., Internet and DSL) even when I have no internet connection.

Is there any way to resolve this problem?

The DSL provider has given up and told me that I will have to pay for any more of their visits regarding this issue.

Incidentally, I lost my internet connection just before I started writing this post and again while I was writing it. Usually the internet comes back up in 2-5 minutes, but this last time it never came back up after 20 minutes, so I had to unplug the power from the modem and then plug it back in to get the internet running again.

Best Answer

I get tons of FEC and CRC errors almost daily.

If you are seeing these errors in the modem logs then it is definitely an issue with the line from the local DSLAM to your house. Only the phone company (if they are also your ISP) can fix this. Them telling you it was an issue with your PC is plain lying.

What are CRC (Cyclic Redundancy Check) Errors?

  • CRC is an error detection code used to verify packet transmission between the sender and receiving end. A CRC error indicates that part of the data packet is corrupt and requires retransmission.
  • Many CRC errors in a short period of time will show a noticeable reduction in throughput speed.
  • This can be an early indication that there is too much noise on the line and in extreme situations can lead to loss of sync (disconnection with the exchange).

What are FEC (Forward Error Correction) Errors?

  • Count of errors that have been corrected due to error correction being applied to the line.
  • Error correction is turned on at the same time as Interleaving.
  • Its normal to see FEC errors on an Interleaved line and rather than anything to be too concerned about its more an indication that the Interleaving & Error Correction process is working and doing what it should.

For more information see xDSL Broadband Data - Error Correction

You might also want to read How to interpret your ADSL Line Stats

So what causes these errors?

  • The length of your telephone line to your local telephone exchange/DSLAM

    • ADSL is capable of supporting download rates of up to 10 Mbps over telephone lines in good condition at line distances of up to 3.4 miles (5.4 kilometres). Bandwidth deteriorates rapidly with line length; which means that broadband-users located beyond 3.8 miles (6 kilometres) from their local telephone exchange are restricted to 1 Mbps or less.
    • ADSL 2 can provide download speeds of up to 12 Mbps over a single copper pair up to 1 mile (1.6 kilometres) from the telephone exchange, or 24Mbps up to 1 mile (1.6 kilometres) using 2 copper pairs bonded together.
    • ADSL 2+ can provide download connection speeds of 26 Mbps within 0.6 miles (1 kilometre) of the telephone exchange, falling to around 12.5 Mbps at a range of 1.1 miles (1.8 kilometres). Bandwidth deteriorates rapidly with line distance beyond 1.6 miles (2.5 kilometres) from the exchange, and at a range of 2.8 miles (4.5 kilometres) it does not offer any speed advantage over ADSL. The number and type of other digital services being used by other customers over copper pairs within the same cable sheath.

  • The configuration and line quality of the copper wire pair between the exchange and your premises.

  • Electrical interference from outside sources (underground phone lines that have to run under very large buildings and motorways can be affected by 'noise', older phone lines that run along telegraph poles also be affected).

  • The configuration and quality of the copper wiring within your premises (use a central splitter for optimal performance).

  • Weather conditions

    • Hot weather can cause a long line to expand.
    • Rain on a connection somewhere could cause dampness and deteriorate the signal.
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