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Let's say that a short in faulty home wiring partially damages the DSL port on a modem... where it still functions, but has intermittent issues. What kind of symptoms would this sort of damage cause? What are the symptoms of a bad DSL modem in general? Would it cause corrupt downloads of files on the computers?

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Unlikely; TCP and the underlying transport layers do error correction. Do you believe you're actually experiencing this? – Wooble Sep 24 '12 at 16:46
Not sure. Internet drops out frequently during wet weather which made me suspect a short in the wiring somewhere. I do get random corrupt files (infrequent but still bothersome) and I'm trying to track down the source. – BobRalph Sep 24 '12 at 17:15
up vote 1 down vote accepted

In broad or general terms, problems caused by physical wiring issues will cause the DSL line to drop and disconnect. Depending on what type of DSL modem you have, you can enter the log of your modem and review the errors reported to it.

Other types of physical level errors will "slow down" your DSL line speed (reduce it's bandwidth) to something far below what you expect or are paying for. Using sites like Speedtest are a good starting point to begin a discussion with your ISP.

File downloads are usually handled in an application that performs some rudimentary form of file checking/verification. And that's in addition to the basic error connection provided in TCP (of TCP/IP). So it's unlikely (but possible) that physical level DSL errors cause file corruption. If they did, the application or TCP would more likely catch and resolve that.

So, if you suspect DSL issues, I would recommend:

  1. Go into the admin/console of your DSL modem and review the log or error reports.
  2. Perform a speed test and see how it compares to what you expect.
  3. Call your ISP/telco and ask them to check the log at their end of your line. You could also ask them to perform some line tests. However, depending on what their level 0 help script is, you may not have much luck there.
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Speed tests are checking out fine. I went into the modem GUI and found the logs. Under "DSL Transport" I found it logged 1 error out of 569276 packets on downstream and 0 on upstream. Under "DSL Channel" it logged 1 CRC error on "near end" and 6 CRC errors on "far end". I'm not sure if it's normal to have errors or not. – BobRalph Sep 24 '12 at 17:12

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