The PCAP recording should optimally begin before the first T.30 Indicator or before the first DIS is sent by the called terminal. Multiple sessions may exist within a PCAP file, so FaxTap for T.38 requires the IP addresses and corresponding ports of the T.38 participants.
The input to the application consists of a recording of T.38 packets saved using the PCAP format output from a packet-snoop program, as well as the address information. Since the recording is made from a packet snoop, the capture 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 Windows Picture and Fax Viewer ®. 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 to begin the extraction. Upon receipt of the command, the PCAP file is opened, and the state machine started. Each packet is processed through the T.38 Frame Classifier. If the frame is a T.38 frame, it is passed to the T.30 event preprocessor which accumulates V.21 frames to produce a T.30 event. Regardless of which T.30 event occurred, the state machine will take appropriate action, safely ignoring some events, while acting upon others. When the T.30 Preprocessor reports DIS, the following High-Speed frames are known to be either ECM or Raw image data. ECM data is accumulated until either a PPS-EOP or PPS-EOP are seen by the T.30 event preprocessor, then sent to the Image Conversion Library to be written to disk. Non-ECM data is immediately passed to the ICL for conversion and storage.