First, let me thank you in public for your assistance, freely given and extremely helpful and educating (to me, anyway... as a part time programmer/webmaster and past airline pilot with technical leanings).
Most DSL modems though will have a status page for the DSL signal. The status page will show the S/N ratio. If you have a condition where the S/N ratio is marginal, it only takes a very modest increase in noise or decrease in signal to bring the signal to noise ratio below what is sufficient to decode the signal.
Sorry, no s/n measurement. I have searched the PDF manual downloaded from Support and gone through all of the tabs and options, there is no s/n measurement. Which is why I asked if there is third-party software to get that valuable measurement.
With DSL, any other device on the line that is not connected through a DSL filter will interfere with the DSL circuit. It's OK to have your 5.1 Ghz phone connected IF it is connected through a DSL filter, but it should not be connected directly without a filter.
All devices attached have filters. But the old anomaly remains, the line still works well 22+ hours a day and suddenly drops out for relatively short periods.
AM broadcast stations and analog VHF TV stations are common causes of interference. These will usually cause audible noise in a telephone as well, you'll either hear the AM station, or you'll here a buzzing sound that changes with picture content with VHF TV stations. Later this month analog VHF TV goes away, so if that's causing you issues, they will be eliminated shortly.
None nearby (that I know of).
So what I would suggest to start with is plug an ordinary phone into the line, through a DSL filter; and during a time when the DSL is down, pick up the phone, hit a touch-tone digit to get rid of dial-tone and listen carefully. You should hear silence; if you hear hum, hiss, crackling, other telephone conversations bleeding over, radio stations, or any other noise; that's a problem and should be reported to the telephone company and fixed.
However, because DSL uses frequencies into the MHZ range, it is entirely possible for an interfering signal to be completely inaudible.
Will do. My wife does hear hoise on her line - which almost drowns out the dial tone - and mine does the same. I smell telco problems, but my provider uses the telco lines and I get the impression the last thing they want to do is ask the telco ANYTHING (probably for $$$$$ reasons).
If your signal is marginal because of bleed-over from another pair in the same binding, sometimes the telco can cut your line to a pair in a different binding. The DSL protocol is such that you can only have so many pairs in a binding equipped with DSL before the cross-talk starts to become excessive and reduces the reach of each circuit.
I go from the external terminal box directly around the house externally to the wall where my computer is. The 2-pair shielded cable I use is marked for telephone use by Radio Shack, and the other pair is not being used. No second pair in use = no noise from that source. And they are shielded, so neither pair is acting as an antenna.
There is also a new DSL protocol, DSL2, that if your DSL circuit isn't already on, can improve S/N somewhat. DSL uses a modulation scheme that breaks the bandwidth down into a bunch of narrow channels with guard bands between the channels. Training determines which of those channels is usable and sets the upstream and downstream speeds accordingly. DSL2 changes the modulation scheme in such a way that the guard bands aren't necessary and the full bandwidth can be used for data, which means for a given data rate, a lower S/N is tolerable.
So an upgrade to DSL2 protocol can be helpful, but I've also seen a lot of modems that have firmware issues that make them not work well with DSL2 when they operated fine with the old DSL, so that's a mixed bag, and usually not an option on a per subscriber basis anyway. It's usually something that happens when the telco replaces a DSLAM with newer equipment.
As indicated, that would be a local telco issue, and probably a big $$$$ issue for my provider. Here in Canada, Ma Bell still rules the roost and seems to charge big bucks even for just answering their phone (if you can ever really speak to an actual real live person - the old-style ones with blood and veins - instead of paging interminably through menus towards your inevitable cut-off dial tone).
Some modems operate better than others under marginal conditions, so if you have a 6DB S/N, and it's loop-length related and not really something fixable; a different brand of modem may provide somewhat better results.
I will bear that in mind... I bought my modem rather than rent it (I tend to think long-term) and once I return this rental one I will seriously consider that. Do you have any recommendations? Are there different equipment signals from different telcos?
And do you have a suggestion for a good recent-reliable model router, one with the s/n status feature? The one I have now does the authentication for me, that would be a major plus, too (I don't need wireless any more).
Again, thank you very much for your help,