Modem sounds during connection?

[tsurikov]

Hi everyone,

I imagine anyone who's used a modem has heard the sounds it makes as it establishes a connection (assuming the modem speaker is on, of course). I've always been curious as to what those sounds mean. Now I don't mean what each millisecond of the sound means. But there seems to be a distinctive and common sequence of noises - you hear the dial tone, then the modem dialing, then about a second of a high-pitched tone, then a "hissing sound" added, then some choppy plucked-string-like noises, maybe something else, then silence as the modem connects. I'm just wondering whether each of those noises can be associated with some step in the connection process - initial response? speed negotiation? etc.? and, for instance, at which point does the modem go silent?

Just wondering!
--Michael

 

[SYAR2003]

Listening to your fax or data modem when you use it. All that staticky-sounding noise and the beeps are literally the handshaking process. These mating calls are negotiations to find the highest terrain from which they can trade bits, with the greatest common denominator of all variables.

If you have your modem's speaker turned on when you connect to the service, you'll hear a painful hissing-screeching sound just before you connect. This is called handshaking; it's the process whereby the two modems (your modem and the provider negotiate the highest speed at which they can reliably communicate with each other. During handshaking, modems compare their own capabilities, and then test the quality of the connection between them to find the highest transmission speed that it can tolerate.

Some modems are programmed to be very aggressive, and will try to start the connection off at a high speed (often being forced to downshift later on). Other modems are more conservative, and will start out slow, gearing up later as line conditions permit.


And the modem goes silent after it has established it's protocol/speed with the host.