Fax and Modem Operating Modes

The device supports two modes of operation:

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Fax/modem negotiation that is not performed during call establishment.

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Voice-band data (VBD) mode for V.152 implementation (see V.152 Support): Fax/modem capabilities are negotiated between the device and the remote endpoint during call establishment. During a call, when a fax/modem signal is detected, transition from voice to VBD (or T.38) is automatically performed and no additional SIP signaling is required. If negotiation fails (i.e., no match is achieved for any of the transport capabilities), fallback to existing logic occurs (according to the parameter IsFaxUsed).