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

Question

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.

Answer 1

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

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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.

Answer 2

My grandfather had this exact situation with his DSL years ago. It took a dozen visits (from myself and other local computer experts and multiple phone company technicians) and replacement of the modem twice, until someone at the ISP realized the problem three years into his subscription...

DSL has a maximum distance that the signal will travel. Different types of DSL have different maximum limits, but in general the maximum distances of all of them are pretty low. If you are outside the maximum distance for your type of service, it is possible that the sales department of the ISP doesn't know that and will happily sell you a subscription that you cannot physically use.

In my grandfather's case, they told him that his distance meant they could not provide the 6Mbps service he was paying for but they could switch his connection to 768kbps and it would work at longer distances.

If your connection previously worked well, it is possible that you were on the very edge of the service area and that construction or other maintenance between you and the DSLAM has lengthened the path of the wires. (I just saw our local phone company do this to make way for a road widening project and the new path of the wires is 50 feet longer than it used to be.)

Answer 3

July 17, 2020

I wanted to give everyone an update. The last I mentioned was that a team leader from the phone company (which provides my DSL service) told me that the problem was my computer and that they would be charging me for any more trips to address the matter. I connected a new computer (as they suggested), but still got tremendous FEC and CRC errors. I reported their company to the state attorney general's office and the Better Business Bureau, but decided to delay any action because they were maintaining contact with me about the matter.

I was still getting disconnections and speed issues over the past 2 months. Finally, they decided to connect my house "directly" to the local switch box across the road. Despite the many previous inspections of the equipment by their "best" people, the cable coming to my house was indeed bad as I had surmised! I've had no disconnections, no CRC errors and only 3000 FEC errors in the past 2 weeks!

Thanks to all of you who provided information, suggestions, or personal experiences to help inform and encourage me regarding this matter. If anything else transpires, I will let you know.

Answer 4

1. You need a tech with a TDR (Time Domain Reflectometer) like this
2. No you dont need to pay for this.
3. Try unplugging the line filters on your phones.
4. They have to fix it whether they like it or not by law or you can’t call emergency services.
5. Your modem should have various readings like Signal to Noise Ratio (SNR)

SNR defines how strong the signal is, compared to interference on the line, some standards/devices/providers/country’s vary slightly but essentially

• Up to 6dB: Bad line, there are synchronization problems.
• 7dB to 10dB: Failures are possible.
• 11dB to 20dB: Good line, no problems with synchronization.
• 21dB to 28dB: Very good line.
• 29dB and Above: Perfect line.

As mentioned earlier the distance from the exchange is important. The biggest killer of ADSL and anything using plain old telephone service (POTS) is distance.

This is called attenuation. Simply put the higher the frequency the shorter the range given that phone wires don’t travel in a straight line to your house. So the further away the line distance is from your house to the DSLAM (Digital Subscriber Line Access Multiplexer) is the worse it gets.

However Most modern ADSL routers will also have a reading on this

• 20dB and Below: Outstanding
• 20dB to 30dB: Excellent
• 30dB to 40dB: Very Good
• 40dB to 50db: OK
• 50dB and Above: Bad

This is not to be confused with signal to noise margin. If your modem will let you configure this, and that it is misconfigured. That can indeed cause connectivity problems, and speed improvements, but no where near the levels you are describing.

Some modems will explicitly state the signal strength in addition to signal to noise ratio. But getting hard numbers on acceptable levels is turning out to be harder than expected; I will keep looking.

Either way any customer facing telecom’s tech worth his salt should not only know this, but also have basic equipment to measure it. If you can configure SNR margin Take a look at speed-guides DSL speed calculator. It may help with refining connections.

700m may not sound very far but it will hurt you badly when they upgrade to G-fast i will be surprised if you get over 50Mb/s you will have to wait for XG-fast or terabit DSL to get better speeds. The ideal G-fast distance is less than 100m

Answer 5

I would lock down the IP addresses in your house. Check that only one device on your network (your main router) is giving out IP addresses (i.e. DHCP is turned on). Anything that can be an access point or repeater or even a phone as an access point for WiFi may give out other IP numbers. What can happen is your router gives out addresses - say 192.168.1.1, 192.168.1.2, 192.168.1.3 then device 2 goes to sleep so the router thinks it has gone away and gives device 4 the IP address 192.168.1.2 and then the original device 2 wakes up and it thinks it is 192.168.1.2, but another device has that so it may get 192.168.1.4 and apps on it may or may not know. So they may or may not work. So what I do is fix the IP addresses for any fixed devices that never go to coffee shops, work or anywhere else - e.g. Televisions with IP addresses, Wii, Kindle, swimming pool controller etc. and tell the router that these devices have fixed IP numbers and also tell the devices that their IP addresses are fixed to these numbers. It will make a more stable network.

Answer 6

FEC are corrected errors. If CRC and ES are both near 0 or actually 0, then it means the connection is stable.

A high FEC (as well as high CRC) indicates there is noise on the line somewhere. This noise if you lucky is local inside your property and you might be able to fix it yourself, could be a faulty electrical device as an example.

If you unlucky it will be outside of your property and likely unable to do anything about it.

On some occasions it might be a faulty line, in which case the provider might be able to fix it, however since on many occasions its not a faulty line and rather just interference, it might take some convincing to get your provider to attempt to fix it.

In addition it could be crosstalk, a form of noise caused by adjacent DSL lines, vectoring can almost nullify this, but not all providers utilise vectoring.

Shorter lines are less likely to have interference but its not a guarantee.