I am getting some pretty high CRC and FEC error rates on my modem. After many tests I am getting 1/5th or less the bandwidth that I should and I started looking into it. It seems I have high packet loss and it seems to be between my modem and the ISP. (As far as I can tell anyways)

What can I do to decrease packet loss and improve speed?

Snapshot of modem details


After moving the modem to a different wall jack, the attenuation has improved and I haven't seen any crc errors. (Yet) My speed has improved about double, however I am still not getting the 45mbps that I should be getting (only getting 8).

  • 1
    You contact your ISP this sort of behavior cannot be solved by you.
    – Ramhound
    Jan 11 '15 at 8:54
  • I am going to contact my ISP to see what they think and see if they can fix the issue. Jan 12 '15 at 19:46

CRC errors are bad, and the fact that those are near end means they are errors the modem picks up on the incoming signal - meaning that the frames coming into the modem are damaged in some way and the modem must request they be resent, which slows down your connection. Upstream margins are also getting a bit high which can lead to instability. You didn't show the rate at which the modem is synced - that can help with diagnosis. Mostly what this looks like is line trouble.

The first thing you want to test is a connection directly to your NID. Find the box where it comes into the house of the street - there will be a test jack on the circuit that your DSL is on. You might need to run an extension cord to get power out there - so plan how to do that before you start moving things around (makes your life easier). Plug the modem in to the test jack and then plug a laptop directly into the modem. Watch the stats on the modem for several hours and see if the errors continue.

If you see no further errors, then the issue is the wiring between the posts on the NID and the wall jack. I'd first replace the jack in the wall, and then if that doesn't work, try replacing the cable.

If you do still see errors at the test jack, then the issue could be the modem or more likely is an issue between the DSLAM and the test jack. This is the point where you call your ISP and ask them to do a plugged/unplugged test (validates the modem) and a line test. They'll see what error codes they receive and go from there.

  • The connection speeds are currently: Down 45.12 Mbps / Up 5.12 Mbps. And thank you for the suggestions. I will start troubleshooting. Jan 12 '15 at 19:33

This can be caused by various things.
Try unplugging power from the DSL Modem, and leaving it unplugged for 30 seconds.
I know that might sound like Voodoo (trying randomish stuff), but really it is known to work in many cases. For instance, the issue might be that some equipment on the phone company's end had an temporary issue and negotiated a lower speed with your equipment. A modem power cycle is the fastest and easiest way to resolve the problem. Things may negotiate again and work fine.

If that fails, try contacting the telephone company. They may be able to perform some troubleshooting of certain issues (like, for example, water in the phone lines) in ways that you cannot do nearly so easily or inexpensively.

If that's no getting you anywhere, then try to provide us with newer details based on what else you've figured out (like what else didn't work).


It is typically due to low SINR. I do not have ball park number of top of my head for DSL (and it depends on the modem, modulation and a lot of stuff. Yet, the typical solution is that you contact your ISP, they remotely check the SNR on your modem and compare it against your neighbors. If it is too low in the area, they need to jack it up the power at the other end, otherwise, there is something wrong with your loop (bad cable, interference at connection points or even bad modem). All of these are typically their responsibility (unless you have bad modem and that is your modem and not their equipment). So your best bet is to call and have a tech come over. You have paid for it (well, sometimes they charge you for a tech coming over...)

  • 1
    ISP support can't identify neighbors of a circuit and randomly run tests on those lines. They don't look at the modem for SNR, those stats are on the DSLAM. ISPs usually charge if the service call results in an NTF or IW issue. Plugged/uplugged tests are the method by which you test the modem, line test will check for various faults on the line, such as bad splices/taps, cross-traffic, voltage/short on the line (either on tip or ring). Cable length and old copper will often cause SNR issues - they can't just "jack up power" to increase the signal - instead they provision a lower line speed.
    – MaQleod
    Jan 15 '15 at 22:31
  • Interesting, it might be area dependent though since I have had issues like that both on DSL and Cable and sometimes they have had a tech coming and replacing a whole section of cable. I think it is rather depending on network management style of different ISPs.
    – Mahdi
    Jan 15 '15 at 22:34
  • It might be. I worked for a nationwide ISP as tier 2 support for DSL and voice. Any time I ordered a tech, it was after the customer ruled out IW or accepted liability for a possible charge if the tech found the issue to be IW. There certainly were many times that it was the cable - but usually we had line tests that showed the type of fault and that gave everyone a better idea of where the problem was (eg, a short indicated it was more likely to be at a cross-connect panel). Any time I've called up Verizon, wave, AT&T, Centurylink, etc, they've all had the same terms.
    – MaQleod
    Jan 15 '15 at 23:00

Put the filter and split the phone/DSL at the point where it comes into you house. Best would be inside the telephone company box if you can. Check out what the box is. Amazon has a few filters than can be used outside or will fit in a teleco box.

You can test to see if this would help you by finding that point where you telephone enters the house and removing all other lines/jacks and direct connecting the DSL modem to the main feed line from the teleco. Make sure only the Modem is plugged in. Any other lines will still cause potential problems.

Depending on how many jacks and how long all the lines are that DSL signal is getting split and unlike the low frequency of a voice phone call all those jacks add a lot of impedance to the high frequency DSL signal.

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