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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting Modems | Call Waiting Problems ]

I want call waiting to interrupt my connection (so I can tell when someone is trying to call in) but it doesn't work

Explanation: You have only one phone line in use for both voice and data calls. You want to be able to use your phone line for your modem, but you also need to be reachable if someone wants to call you. You were hoping that by getting call waiting, this would enable an incoming call to knock off your modem connection when necessary so you could get your voice calls, but it does not seem to work.

Diagnosis: When a call comes through on call waiting, an audible beep is generated that indicates the incoming call. To the modem, this is just an interruption of the signal, and many older modems would immediately terminate their connection with the remote host upon detecting it. The "problem" here is that many modems today have advanced error-detection capabilities that allow them to maintain a connection despite this sort of line noise. When a modem does this, you will experience a pause of a few seconds as the modem recovers from the interruption, but the call will continue. There often is not much you can do about this.


  • The flippant answer of course is to get a second phone line, but you probably knew that already. :^)
  • There may be an obscure parameter that you can tweak for your modem, that controls the error-correction level or the amount of time that the connection can be interrupted before the call is terminated.
  • If you are expecting a call on the line, and if your connections normally work without often experiencing pauses, you can pay attention to the response time and voluntarily terminate the call when you start noticing pauses that might indicate someone on call waiting. The problem of course is that this is a hassle, and in addition, the pausing might not be call waiting at all.
  • If you are willing to tolerate hearing the static from the modem while you are using it, you can set the modem volume control to stay on during your whole connection, using this command: "ATM2". Then, if you get a call waiting beep on the line, you'll hear this as an interruption in the usual static of the modem, and the modem will "renegotiate" the connection. This will sound similar to the tones you usually hear when the modem is first connecting. When you hear this sound, it may be call waiting, although it might not be. You can decide if you want to terminate the connection and pick up the phone to get the incoming call. If you use "ATM2L1", this will keep the modem on but at the lowest volume setting.
  • You could replace your modem with one that will cut off after a call waiting ring-in. In particular, 14.4 KB or older modems are more likely to do this than newer 28.8 KB or higher ones. Needless to say, this is far from an ideal solution.

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