The PCM recording may begin during the Called Terminal Identification (CED) tone or may contain other tones, such as ringback, before the actual fax negotiation begins. Typically, recording begins once the CED tone has been detected.
The input signal to the application consists of 16-bit linear PCM samples in little-endian format. Since the recording is made from a line tap, the signal will contain both sides of the fax session.
The output of the conversion has two parts. The rendered image is delivered to the calling application in TIFF-F format, which can be viewed by any TIFF-F viewer, such as Imaging for Windows®. The second part of the output is a report containing the information in the table below.
||NO_FAX: Input is not a fax signal (no V.21 flags detected).
FAX_NO_PAGES: Input is a fax signal but no pages were recovered.
COMPLETE_SUCCESS: All pages recovered had less than 10% bad lines.
PARTIAL_SUCCESS: At least one page had more than 10% bad lines.
NSS_MODE_ON: Session is using non-standard facilities as opposed to T.30.
||2400, 4800, 7200, 9600, 12000, or 14400 bits per second.
||HIGH (204x196dpi), LOW (204x98dpi), or SUPER_HIGH (204x391dpi).
||Modified Huffman (MH), Modified READ (MR), or Modified-Modified READ (MMR) encoding.
||A4, B4, or A3.
||The number of bad lines received.
||The total number of lines.
||The number of pages processed.
||The number of bytes processed by the high-speed (non-V.21) modem.
||The number of training signals processed.
|Document File Name
||The name of the current file processed.
||The sending fax machine identification number.
||The receiving fax machine identification number.
As shown in the diagram below, the application’s command is received by the Controller, which starts the V.21 receiver in order to decode the answering terminal’s Digital Identification Signal (DIS). DIS informs the caller of the capabilities of the answering terminal. The ensuing Digital Command Signal (DCS) from the caller is decoded to determine such details as modem to train, image resolution, encoding, page size, and so on. The appropriate image modem’s training is then initiated. Modem events, such DIS, DCS, and Train End, are sent from the Controller to the event preprocessor and from there to the system’s state machine, which is used to determine the next course of action. Image data are then sent to the Image Conversion Library, where the image is converted, as necessary, for storage in the output TIFF-F.