Symptoms
- DSL modem's 'sync' or 'DSL' light drops and reconnects periodically
- Internet works then suddenly stops for a period before returning
- Phone line has crackling or noise during calls, if you also have landline phone service
- Modem shows lower sync speed than expected for your plan
Likely causes
- CommonMissing or faulty DSL line filters on phone jacks sharing the lineEvery phone (not fax or alarm) connected to the same line as the DSL needs a filter, or it can introduce noise that disrupts the DSL signal.
- CommonLine noise or interference on the phone line itselfOld or degraded wiring inside or outside the home can introduce electrical noise that disrupts a sensitive DSL signal.
- PossibleDistance from the phone company's central office or DSL equipmentDSL signal quality and speed degrade significantly with distance from the provider's nearest equipment, which can cause borderline connections to drop intermittently.
- PossibleModem needs a restart or has an aging componentLike other modems, DSL modems can develop age-related connection issues.
What to do
- Confirm every phone, fax machine, or other device sharing the line (except the DSL modem itself) has a DSL filter installed on its jack.
- Connect the DSL modem directly to the primary phone jack (often called the 'network interface device' jack) where the line enters the house, bypassing any internal wiring or splitters if possible.
- Restart the DSL modem by unplugging it for 30 seconds and letting it re-sync, which can take a few minutes for DSL specifically.
- Check the modem's admin page for line statistics like 'sync speed,' 'attenuation,' and 'SNR margin,' which can indicate a marginal line if attenuation is high or SNR margin is low.
- If you also have a landline, listen for crackling or static on calls, which suggests line noise that could also be disrupting DSL.
- Try a different DSL filter if you suspect the current one may be faulty.
- If line statistics indicate a marginal or noisy line, or the connection drops persist despite these checks, contact your ISP for a line test and possible technician visit, since DSL faults are often in the physical wiring.
Tools and parts
- DSL line filters
DSL line filterSearch: “dsl phone line filter”
When to call a pro
If the modem's line statistics show high attenuation or low SNR margin, or drops continue despite proper filtering, your phone company needs to test and likely repair the physical line.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.