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I have just installed a new modem/router at home and after doing some testing I noticed that if I plug the modem directly into the master socket in my flat I get around 4MBits and the logs look like this:

Update Counter : 137
Modulation : ADSL2+
Annex Mode : Annex A/L
Line State : up
Lan Tx : 15679
Lan Rx : 10384
ADSL Tx : 335
ADSL Rx : 459
CRC Down : 0
CRC Up : 0
FEC Down : 0
FEC Up : 0
HEC Down : 0
HEC Up : 0
SNR Up : 12.1
SNR Down : 12.0
Line Attenuation Up : 34.3
Line Attenuation Down : 56.0
Data Rate Up : 801
Data Rate Down : 4138

whereas when I plug it into a normal socket, even the one covering the master socket, I get only half of this speed:

Update Counter : 52
Modulation : ADSL2+
Annex Mode : Annex A/L
Line State : up
Lan Tx : 1681
Lan Rx : 799
ADSL Tx : 538
ADSL Rx : 827
CRC Down : 0
CRC Up : 2
FEC Down : 0
FEC Up : 686
HEC Down : 1
HEC Up : 0
SNR Up : 12.3
SNR Down : 11.7
Line Attenuation Up : 29.4
Line Attenuation Down : 55.0
Data Rate Up : 784
Data Rate Down : 2342

I even tried plugging in the filter and phone into the master socket, and it still works fast. Plugging in only the modem into the normal socket doesn't help - it is still slow.

Can I do something to fix this problem?

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migrated from Nov 28 '12 at 6:55

This question came from our site for system and network administrators.

If I understand your description, it would appear that when you connect your dwelling's existing telephony wiring to the telco demarcation (master socket?), your signal and performance degrades. Things that degrade the performance of a copper network are unterminated leads, unfiltered jacks, loose connections, cable runs alongside a noise source (electrical cable, fluorescent lamps, etc.), broken insulators, broken or pinched wires, faulty phones/faxes/modems, cheap splitters, poorly wired junction boxes; I could go on...

Worse, is that most of these are hidden behind walls, beneath floors, above ceilings, often with no one junction point, let alone a box, or punch-down block.

One way of troubleshooting such a network is by systematically isolating each portion of wiring, much in the way you've already done, by disconnecting most of it and then reconnecting portions until the troublesome part is found. Right now, you know the problem is not one phone, nor your DSL modem. Next, you might want to either try for the easy win, and unplug all other phones and devices from their sockets, to see if one of them might be leaking noise onto the lines, or you can find the nearest junction point to the master socket, isolating it (*) and testing your signal to see if the trouble is coming from the now isolated portion.

(*) I noticed you mentioned 'your flat' which I understand to be an apartment. This may be a job for your landlord or maintenance staff, since you can clearly demonstrate that the problem is in the building wiring, not your equipment or the provider's line.

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