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March 20, 2010 1:35 PM   Subscribe

Got my connectivity/internet issues fixed yesterday. But what was the problem? I don't understand what the tech guy told me.

For the last two months (after four months of being fine), my internet would cut out and back on intermittently (it's a DSL line, one PC, not a wireless setup). After phone troubleshooting didn't solve the problem, a visit from my IP only confirmed everything was hooked up properly, and a visit from the monolithic phone company that owns the transmission lines advised there was nothing wrong with the lines, the IP and the monolith came out together for a "vendor meet."

After working on it for an hour and a half, the IP guy informed me that they "pretty much know what the problem is." He said, "The stress levels were just ridiculously high. It was up to 50! But we got it down to 20, which is acceptable." I asked him to clarify what he meant by "stress" and he unhelpfully offered "noise."

"Part of the problem," he said, "is, this building you live in is very, VERY old. (true). And the phone box, the connector terminal outside we've been working on, is also very old. The wires are fine, though." He said that he didn't know if the stress level would go back up again, but he couldn't promise that he couldn't. He could only treat the disease, not cure it.

And that could be fine because I most likely will not be living here much longer.

But...

1) What does he mean by stress/noise? I assume interference, but what kind of interference, and how does that correlate to the oldness of the house and phone box?

2) What do the 20/50 measurements refer to?

3) Is there anything I can do myself to cut down on the stress/noise?
posted by mreleganza to Computers & Internet (5 answers total) 1 user marked this as a favorite
 
Perhaps he meant 20/50 Ohms of resistance in the degraded metal connectors of the old equipment, causing signal degradation ("noise")?
posted by bizwank at 2:19 PM on March 20, 2010


It's ISP (as in Internet Service Provider), not IP (as in Internet Protocol).

Noise is omnipresent in communications. You can get noise from anything:

- natural interference: lightning, cloud cover, solar storms (increased activity from the sun), random cosmic particles, radio active decay (uranium is pretty evenly distributed on the surface of earth).

- man made: power lines, cross talk from other communication lines (cable, other phone lines), induction motors (remember getting static on the TV when you turned on the blender?)... the list goes on an on.

- old age: old wire get brittle & damage, terminals are corroded, people patching the system do a poor job, old equipment fails, etc.

All these things manifest as noise in your line. Usually noise is measured as a "signal to noise ratio". That is, take the amount of signal you're receiving, divide it by the amount of noise, and there's your number! A higher number means more signal, and a lower means less.

An equivalent number you also see in communications (and DSL) is the signal dB. There's some math involved to get this number, but again, higher is better.

I think what you're ISP tech was referring too, however, was now the SNR but the line attenuation. Line attenuation is how much power is lost. Obviously, you want to lose as little power as possible. So in this case a lower number is better. And indeed, 50 sucks.

The farther you are from your teleco's Central Office (where it keeps its hardware in your neighborhood) then the more line attenuation you'll have. Bad contacts for the building also decrease line attenuation. As does improper/substandard wiring in the building and too many jacks/devices on the circuit.
posted by sbutler at 2:22 PM on March 20, 2010


I'm not completely certain what they were talking about, but since nobody else has answered yet I'll take a shot at a rough-and-ready, semi-educated tl;dr.

1) One likely explanation is that the connections between the line coming in and your building's internal wiring, which was described as "very VERY old", are corroded, and deliver a degraded signal to your computer. Maybe they literally cleaned all the contacts to provide better physical seating and less electrical interference; maybe they've got some sort of in-line signal analysis software/hardware that can detect and to some degree tune or filter the transmission signal to compensate for the fact that a certain percentage of packets don't get delivered cleanly to the DSL modem in your room and report back a "didn't make it through" notice.

2) Could be points on some scale (i.e. 0 is a perfect clean strong signal, 100 is nothing but static); or signal-to-noise ratios...

3) Move. :-) The "stress" is caused by imperfections in the physical path the electronic signal takes - including your old building's crappy innards. Telephone signals are much less precise than digital data, and voice connections can tolerate a reasonably high degree of interference/distortion and still be coherent to our ears, so the condition and quality of the wiring didn't used to be as critical as it is for your Internet connection. Unless you can manage to get all the old wiring stripped out and completely replaced with shiny new high-quality (expensive) ones, you're stuck with what you've got.
posted by Greg_Ace at 2:42 PM on March 20, 2010


I am not sure either, but they might have been talking about the line attenuation rate, measured in dBs (decibels). I am not a telecoms engineer, but my understanding is that this is a measure of how much of the signal get degraded between your house and the exchange. This causes dropped packets and after a certain point, the signal is degraded enough to make DSL unworkable.

According to this, anything over 50dB is considered poor, whereas 20dB is excellent.
posted by AndrewStephens at 4:02 PM on March 20, 2010


Old phone lines were installed and designed with only one thing in mind: voice service, which is about the equivalent of 64 kilobits per second. DSL takes those old lines and squeezes out of them much higher bandwidth by utilizing a much wider range (or band) of frequencies, thus broad-band. A lot of the wiring technologies used in the distant past are just fine for voice service but cause great harm for DSL.
posted by Rhomboid at 4:57 PM on March 20, 2010


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