I have 12 MBit DSL service at home. At some point it was changed to 14 MBit without my knowledge.

Then, two days ago my connection went completely down. The provider moved it to 12 MBit but I still couldn't get a connection. Today it was set to 7 MBit and I now have a connection, but I am trying to find out why it suddenly couldn't handle the capacity.

A technician tested my line at the demarcation point outside and said it could handle 14 MBit, and suggested it was the modem failing. Is this possible for a modem to slowly lose speed over time? Is there any way I can test it at home to confirm this?

I know the usual suggestion is to try it on a friend's line but this is not an option. I would love a sure-fire way of checking the modem to see if it is truly "dying" or it is something on the provider's end.


  • It's a 4-5 year old Thomson Speedtouch 516 (ST516). This can handle adls2+ e.g. up to 15mbit. It was provided from my ISP and I confirmed with them it can handle these speeds (and again, it was for 5 months at 12mbit no problems)
  • I've tried rebooting, resetting, connecting directly to computer, different jacks, etc
  • nothing else on the phone lines in the house
  • the stats below seem to have A LOT of errors e.g. FEC erros at 588 million. what does that mean??

Here are the current stats:

Uptime: 0 days, 15:22:19
Modulation: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 824 / 7.293
Data Transferred (Sent/Received) [KB/KB]: 0,00 / 0,00
Output Power (Up/Down) [dBm]: 12,5 / 6,5
Line Attenuation (Up/Down) [dB]: 8,0 / 29,5
SN Margin (Up/Down) [dB]: 8,5 / 7,0
Vendor ID (Local/Remote): TMMB / IKNS
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 4 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 40 / 0
FEC Errors (Up/Down): 0 / 588.855.513
CRC Errors (Up/Down): 3.342.340 / 0
HEC Errors (Up/Down): 0 / 0

  • 1
    Are you sure it's the modem? How exactly are you connecting? I had to buy a new router after my ISP was going from 12 to 25 MBit/s. – slhck Feb 16 '12 at 22:40
  • 1
    What modem do you have? – David Schwartz Feb 17 '12 at 0:03
  • @MorganTiley Your Attenuation is low,there is something giving you feedback on the line. Also, the modem is quite old and most likely to old for new firmware releases to handle ADSL2+ traffic.. – onxx Feb 20 '12 at 6:11

Unless it's a business line it's only a throughput speed - they won't guarantee it regardless of what the tech said.

Please verify whether this is DSL-cable or DSL-landline?

There is an array of tests that can be performed as well as fixes - these are limited to what you can do yourself.


  1. Factory reset modem
    • test connection with only one computer
    • connection should be directly connected(wired) to modem
  2. Unplug all handsets(DSL-Line)
  3. Connection point. Should be the first point in your place.
  4. In your modem status/statistics check your line attenuation, this will tell what sorts of nosie feedback is on your phone line.

Fixes (common):

  1. Change the connection point of the modem
  2. Remove all handset phones (DSL - landline) to identify suspect noise
  3. Port rebuild (ISP side)

If still no success you should call your ISP's support line, as they have an array of tools and monitoring that will give them more information and solutions.

Modem slowness usually has two issues: either the incorrect/out-dated firmware or the age. The typical ISP rule of thumb is that you should be upgrading your modem firmware every 6-12 months and when that doesn't fix the issue (varies per: model, make and time of production between 2 and 3 years), replace your modem.

| improve this answer | |
  • 2
    By definition, DSL runs over POTS land lines, not cable. – psusi Feb 17 '12 at 2:06
  • 2
    @psusi Yes by definition, however it is very loosely used by alot of ISPs as well as the term Broadband internet. Confusing all consumers who subscribe to the service. – onxx Feb 17 '12 at 2:20
  • Thanks @onxx I have tried all of these things already. So I guess there is no sure-fire way to test if the modem is dying. What a funny thing. It has caused me days of headache and I'm sure it's happening to many others as well. Next question will be what is the most stable adsl2+ modem to buy??? :) – Morgan T. Feb 17 '12 at 12:27
  • @MorganTiley Personally as a net engineer, I use a Cisco 877W which lets me to do everything but could be out of your knowledge range. On the other hand I would definitely shop around. Not all modems will fit your needs. Some are better at gaming and torrents than others, I have had a lot of issues with some of the over the shelf routers.. Look into belkin, Netgear, I havent heard much about the new cisco valets... could be worth a shot. – onxx Feb 17 '12 at 23:39
  • The correct terms would be dry loop or lineshare. If it is lineshare, you require filters, if it is a dry loop, you don't. You should also define attenuation and what signal to noise ratio means and what should be alarming. Changing the connection point should be further specified to include the NID. ISP can do a lot more than a port rebuild (and will do most of it first). Your guide really doesn't specify what any of these steps are supposed to accomplish and how to proceed from what is learned. The fixes are also really just more troubleshooting steps. – MaQleod May 1 '12 at 3:27

If they change station to ADSL2+ your ADSL1 modem (10 years old?) will be thing of the past. Calling is the best.

| improve this answer | |
  • This explanation best fits the information we have. ADSL1 maxes out at 8Mbps. – David Schwartz Feb 17 '12 at 0:04
  • Call your provider, tell the modem type you have. ADSL2+ (usually compatible with ADSL1 equipment at provider) modem-only with one or two ethernet ports would cost in range 15-20$/€, more practical would be finding ADSL2+ modem+wifi that works with openwrt and/or dd-wrt and probably has USB port for printer... wireless G is enough for DSL of today – ZaB Feb 17 '12 at 9:26
  • 1
    hey guys - thank you. see my updates. the modem was handling 12mbit for 5 months without issue. – Morgan T. Feb 17 '12 at 12:24
  • Cable Fault: FEC Errors (Up/Down): 0 / 588.855.513 CRC Errors (Up/Down): 3.342.340 / 0 – ZaB Feb 18 '12 at 2:17
  • hey @ZaB does that 100% mean there is a cable issue? – Morgan T. Feb 18 '12 at 2:51

Most network devices have some kind of logging facilities. Try to access your modem and have a look at the logs.

Another option may be getting SNMP data (snmpwalk, snmpget) in order to get information about the status of the modem.

| improve this answer | |
  • Could you expand on this a bit? What would I look for in the logging? What would SNMP data show me and how would I use these commands (I'm on Windows 7) – Morgan T. Feb 16 '12 at 22:15
  • 1
    I doubt at this level you would need the use of SNMP to gather information for home use and would be a little overkil. Checking your logs would be a good idea and then clearing them, which can also cause your modem to slow down. – onxx Feb 17 '12 at 2:24

I have 12 MBit DSL service at home.

This shows your modem was once capable of 12Mbps.

Today it was set to 7 MBit and I now have a connection

This shows your modem is no longer capable of 12Mbps, for one of two reasons: it's failing, or it is no longer compatible with the equipment on the other end (perhaps due to an upgrade).

Is this possible for a modem to slowly lose speed over time?

Yes. All things fail over time. Except for my hair dryers, which fail suddenly and without warning.


  • Reset the modem to factory default. Reconfigure it and put it back on the circuit. If it works, leave it alone. If not, check for firmware updates and install them, if any.

  • Best practice is to just call your provider, give them the modem's model number, and ask if it should work or not.

| improve this answer | |
  • +1 for hair dryer and logic breakdown. You are correct on your points. Unfortunately the ISP is telling me to test it on a friend's connection which isn't possible. It looks like I'll just be buying a new one. – Morgan T. Feb 17 '12 at 12:21
  • Their logic of testing the modem on a friend's connection is weak. What if the friend is on a different DSLAM with different equipment? The friend's connection would have to be identical to yours to provide any meaningful information. – goblinbox Feb 17 '12 at 19:26
  1. Check the documentation for the modem to see if there are any known capacities or issues.
  2. Try sending a ping to outside of your network just to see if by chance you're dropping packets.
  3. Check the logs on the device. Checking the logs will vary by device but should give you a fairly detailed look into what's been going on.
  4. Try http://www.speedtest.net to see what your testing bandwidth looks like so you have actual numbers to test against.
  5. Get a hold of a port tester. They're usually pretty inexpensive and will let you know if the port is dying and what sort of traffic is moving through it.
| improve this answer | |
  • hmm, #5 seems interesting. so I would test the port on the modem itself? What does 'dying' mean in this case? just dropped packets? anything else?. Nothing in the logs. – Morgan T. Feb 17 '12 at 12:17
  • A port tester would only test the ethernet port, not the modem, and you can find out if that's working properly by looking at the error count in ifconfig ( ipconfig on windows ) – psusi Feb 18 '12 at 2:18

Have your provider replace the modem. Either that will fix it, or tell you the problem is elsewhere.

| improve this answer | |
  • Thats on the assumption the modem is still under provider warranty. – onxx Feb 17 '12 at 2:21
  • Yes unfortunately I bought it from my ISP years ago. And they do not rent modems. They suggest I try it at a friend's house to validate it but that is just not possible. – Morgan T. Feb 17 '12 at 12:19
  • You should expect to replace your ADSL modem every 1 to 5 years. They are designed for obsolescence. Go buy another modem already. ;-) – goblinbox Feb 17 '12 at 19:28
  • @goblinbox No wonder humanity is dive bombing... :) – onxx Feb 17 '12 at 23:38
  • @onxx, odd, every provider I've ever seen furnishes the modem. – psusi Feb 18 '12 at 2:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.