Our technicians attend a startling number of jobs each week to stop ADSL modem drop outs and increase internet speeds by simply swapping out corroded telephone sockets for new ones. Customers are happy not only because their NBN or ADSL2+ internet and landline phone are now working at optimum levels, but that the overall cost of repairing the problem was affordable and fast. But why?
Moisture, Oxygen, Metals and xDSL
First please note, the term xDSL refers to a whole bunch of different internet technologies that run over the old Copper phone lines, including the more famous ADSL and ADSL2+ along with the less popular SHDSL and VDSL, usually reserved for commercial (business) internet connections (and VDSL might be used on some NBN connections soon). The following article affects all these services in the same way, but below, we will stick to the well-known term "ADSL".
The PSTN phone network, a.k.a. the Telstra Copper network (which has been taken over by the NBN who is using it for FTTN and FTTB services), is made up of copper and aluminium wires and other metallic bits and pieces, such as distribution frames (MDF, IDF) and, at the end of the line, phone sockets, where you plug in your phone and ADSL modem. If you know anything about electrical circuits, metal needs to touch metal in order for a circuit to be completed: to allow current / electrons to flow through the circuit. Internet data flowing through your ADSL service is actually electrical current whipping through your phone cables!
Corrosion between metallic contacts, terminations and wires causes a change in impedance which affects both Voice signals (either by inducing crackling noises on the line with high impedance between metallic contacts, or with a low impedance short-circuit across the line which drops out your calls and drops out dial tone so you can’t make calls) and ADSL data signals (by causing a whole bunch of high frequency noise on a specific “channel” or range of frequencies that causes dropped packets / error packets, or causes the modem to disconnect and mark those channels/frequencies as “too noisy”, reducing your overall bandwidth - reducing your sync speed, and ultimately, your data throughput / actual download speed).
The changes in impedance are basically how hard or how easy the current, or electrons, can flow through your phone line's "circuit" between your home and the Telephone Exchange. When corrosion is dry, it acts like an insulator, preventing current flow and increasing impedance. When corrosion is moist, the water (and the chemical salt which is a byproduct of the oxidation reaction) lowers the impedance, allowing current to flow. How your line is affected depends on how bad the corrosion is and even the humidity in the room (if the corrosion is inside your premises), or whether it is raining outside (if the corrosion is somewhere on the Copper network, outside in a pit or pillar). This is why ADSL and phone faults can so often be intermittent - your internet drops out or becomes slow sometimes, or perhaps your phone line is noisy sometimes but quiet at other times.
What does corrosion look like?
Here is a photo of an old Australian 610 type phone socket. You can see the green/blue coating on the screws and the crusty bits on the contacts. That's the copper “rust”, not coloured orange/red like what you're used to thinking when you hear the term "rust" (as in, rusty iron), however it's the same chemical reaction - oxidation between a metal & oxygen - in the presence of water.
Although it is important to note that corrosion isn't only limited to the old phone sockets. The smaller "American-type" RJxx (RJ11, RJ12, RJ45) sockets are also prone as they have metallic parts inside. But the old 610 sockets are still rather common in homes and businesses across Australia; we found this particular one in a typical 40-50 year-old Sydney apartment block inside the bottom-floor unit, in a suburb not too far from the coast. This is a typical problem with units/flats/apartments as the ventilation (in older buildings, and some newer buildings too unfortunately) is usually not too good, especially in winter when all the doors and windows are shut and the tenants are cooking and making cups of tea, filling the room with steam.
If your ADSL internet is slow or dropping out, and/or if your phone line is crackling (and perhaps you lose dial tone when it rains?) then you could have corrosion in your phone sockets - if you're in the Sydney metropolitan area in NSW, contact Cabled After Hours to get your sockets and terminations checked by an experienced, qualified Technician who uses and recommends quality parts and materials.
Please make sure whoever works on your phone line (i.e. who changes your phone sockets) is licenced and registered as required by Australian Federal Law. Metallic parts connected to the phone line pose an electrocution hazard, which can be lethal to pets and small children - don't take the risk.