Various factors can lead to CRC errors during an ADSL connection.
Various factors can lead to CRC errors during an ADSL connection.
I repeatedly ask similar questions and never receive a clear solution. What leads to CRC errors? This is the DSL log you provided. I checked the cable from the local box all the way to the end. No obvious damage was found. The wire seemed solid despite minimal copper content. I also inspected and cleaned the connections near the DSL modem and splitter. The signal-to-noise ratio isn’t great, but it appears normal. Line loss is quite high. I have two phones connected through an ADSL splitter on the line (one close to the modem, another elsewhere). Occasionally I see CRC errors, sometimes even without any phones or a splitter—just the modem plugged in. Assuming the connection is solid from start to finish and the local box works fine, what might be causing these CRC issues? CRC can range from one to thousands of errors per second, mainly on the downstream side. It’s also worth noting that I should ideally reach 2045 kbps upload, but the poor downstream SNR prevents the ISP from enabling Annex M modulation, which would otherwise improve the downstream performance and keep the SNR higher.
I believe you're repeating your own explanation. The signal quality is poor, leading to a high noise level that results in transmission errors, which you observe as CRC errors. This interference might stem from faulty wiring or shielding at home, or it could come from outside the property entirely—anywhere along the line between the modem and the ISP. Unless you can pinpoint the exact source within your home, fixing the issue will be difficult.
It often depends on your location and whether the ISP handled the setup correctly. Many American providers have moved away from copper connections, like AT&T discontinuing ADSL and Verizon abandoning copper infrastructure. If the fault lies with the ISP, you may have limited options. The way the service was installed matters—some systems used a device called a NID to link the provider’s wiring to your home. Gaining access to the NID could let you disconnect your own wiring and test the issue. If the problem disappears after that, the fault is likely in your home wiring. Otherwise, the responsibility lies with the ISP.
When a corrupted packet is found and discarded, CRCs increase. Various factors can damage packets; with strong SNR and low loss you should perform well unless readings vary. Are your CRCs inconsistent or gradual? If they appear regularly, could your connection be overloaded during those periods? Overloading may trigger CRCs too. Have you reported the issue to your ISP for remote diagnostics? There might be a tap at the bridge between your line and home. They can also adjust DSL settings to see if improvements occur, though they’ll only act if they notice problems on their side. Residential DSL is unlikely to receive priority from higher-level technicians.
Additionally, packets tend to be lightweight unless there are numerous consecutive CRC failures. Issues can stem from simple causes like someone driving nearby with a faulty alternator, using old power tools, or running a washing machine. It’s not worth trying to block them unless your connection is noticeably slowing down permanently, because you’d need to maintain that slowdown instead of dealing with temporary speed drops from errors.
Thank you everyone. The 6-7 SNR margin is actually reasonable, and the signal quality is quite good. I also noted that the problem seems to be on my home line rather than from the external box, though I couldn't pinpoint the exact cause. Even though I think my country's telecom provider isn't doing enough, they're the only available option nationwide. The CRC count can fluctuate significantly—ranging from one error per hour to thousands at once, with bursts like 200 followed by 300 or more. This kind of saturation doesn’t seem linked to CRC errors in my case. However, I suspect the issue might be related to interference from nearby electricity wires and iron. I checked this multiple times, and it appears the CRC starts when electricity flows through those conductors. I’ve confirmed this three times, and it seems the flow of electricity triggers the counting. Unfortunately, I can’t move the wires to avoid it, but I’m exploring ways to reduce interference. One idea is replacing the affected section with a thicker wire—specifically 16 AWG copper, which is much more robust. I’m wondering if changing the wire thickness could help mitigate the problem. My country, Syria, has limited availability of quality telephone wires, and options are scarce. If I switch to a thicker wire, will that really solve the interference? Or is the wire size less important than the material? I might need to get some DIY experience since I’m in a challenging environment with few resources.
CAT5e ethernet cables perform significantly better than phone lines, which could be beneficial. Smaller conductor size lowers signal loss (difference usually minor in a home), and fewer twists in the cable reduce interference. Shielded cables may offer extra protection, but ensure a solid ground connection at one end. If possible, keep the cable a bit farther from main power lines and avoid running it parallel to them.