Conundrum...

[seawasp]

We have new phones. These phones and the old phones have recently developed a very peculiar symptom. They can dial out and make calls. They can receive calls. But what they CAN'T do is progress through the classic phone menus ("Dial extension 25").

Kathy talked to one of the service people and he claims this has to do with a failure of the modem in the house. But I simply can't believe that, because it makes no sense at all. All other services (cable, internet, and regular phone operation) are fine. How is it possible that the modem could fail to recognize the EXACT SAME SIGNALS from the EXACT SAME PHONE *only* when that phone is trying to enter the signals when connected to some other number?

Now *I* can think of one way that could happen -- if the phones are sending ANALOG signals rather than standard tones, like a dial phone. Then it'd be sending a very fast series of clicks instead of a tone -- perfectly legit for dialing, but not at all workable for the pushbutton menus.  

However, I don't see a switch anywhere that could be an analog-digital switch.

Any ideas? Am I WRONG WRONG WRONG and it IS a strange modem failure (and if so, how?)

Comments

[kengr]

Most phone companies charge *extra* to support pulse dialing. You could look for a pulse/tone switch on the *phones*.

More likely, in my mind is that the modem or the ISP are "deliberately" not passing DTMF tones after a call connects. I have vague memories of that being an option used in some switching gear at one time to try to slow down phone phreakers. But that was a *long* time ago, and if the option exists in modern gear its likely to be a legacy option.

Thus my use of quotes around deliberately. *If* that option has been enabled, it's likely a goof on someones part.

Also, they may be trying to cheap out on bandwidth and thus not using a full 64k bandwidth for each voice channel. Which could mangle the DTMF tones. In that case, it's an issue of the DTMF getting translated *at the modem* when you are dialing.

But once connected, *all* audio, including DTMF tones from your phones get sent as digitized audio, and if the digitization is too "sloppy", then the tones won't be properly reconstructed at the far end.

That *would* be a modem issue. Or a settings issue.

If you can try the phones elsewhere, that'd eliminate them as the cause. But since the tech suggested it's a modem issue, then if you are using an ISP supplied modem, getting it swapped should be free. If you own the modem, then things suck.

[kpreid.livejournal.com]

First, I'll second what kengr said: Unless your "modem" (I assume you mean you're using digital phone service) is being cleverer than it needs to be, your phone is generating a DTMF tone when you push a button — the exact tone you hear — and that tone is digitized just like all other audio over the connection; it is not being recognized specifically by your modem. (On the other hand, it's possible that it does recognize DTMF strictly for the purpose of saving bandwidth; I'm not familiar enough with phone equipment to judge the plausibility of this well.)

If your phones are using pulse-dialing, you would hear the difference. And it's unlikely any “new” phone would even have the option to do that.

A troubleshooting suggestion: call a friend, push a button, and have them tell you whether the tone is clear; compare to them receiving a similar call from somewhere other than your house. (To make sure they stay friends, explain what you're doing before you push the button.)

Better yet, call a friend with a spectrum analyzer. You have those, right? DTMF tones are actually two mixed pure tones identifying a row and column of the keypad; here's the specific frequencies.

[kpreid.livejournal.com]

Addendum: what you called "ANALOG signals" and "standard tones" are ordinarily known as "pulse dialing" and "tone dialing".

(Pulse dialing is arguably more digital than tone dialing, in that the decoder is just counting pulses, rather than filtering and matching specific frequencies! Have a Strowger switch. (I've got a mild peeve about the confusion of “digital” with “electronic”...))