Using Media Priorities While Probing

Unknown applications should take care to use default priorities given in the table in the preceding topic, An Unknown Application Is Running, when probing for applications to take calls of unknown media modes. One reason to do this is to protect human callers from hearing unpleasant fax or modem signals. If, for example, both the INTERACTIVEVOICE and the G3FAX bits are set in LINEMEDIAMODE_, a human caller may still be on the other end of the line. The application should wait to start probing for a fax (with a fax tone) until it is sure that the call is not a voice call. The way to be sure is to probe first for voice, which occurs automatically if following the order stated in the default media-mode list.

However, while probing for high-priority media modes, it is a good idea to turn media monitoring on. This feature, invoked by calling lineMonitorMedia, detects signals that indicate other media. For example, one application may be playing an outgoing "leave a message" voice message while the incoming call starts sending a fax "calling" tone and waits for a handshake. In order not to lose the fax call, the local application needs to be monitoring for this tone while playing the voice message. Determining the lower-priority media (the fax call) while actively probing for the higher-priority media (voice) is not only a safer methodit helps prevent the loss of a callit is efficient because it can shorten the probing process.

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