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Overall Feature Description
The current implementation of the Dialogic Brooktrout product provides support for two T4 timer modes. The modes are set via the keyword t4_timer_mode in the user configuration file. Mode 0 is the original mode which will adapt the T4 timer using an algorithm based on the attempt number, the duration to receive the last response or the T4 timeout value if no response is received and the T4 timer value which was used to set the T4 timer after sending a command to the remote fax machine. Mode 1 is a new mode which was implemented recently, which initializes the T4 timer value but doesn't adapt the T4 timer.
For the new mode 2 (t4_timer_mode = 2) there is only one T4 timer value for the different attempts, instead of three. If the fax session is the originator and the keyword t4_xmit_timer is not in the user configuration file or is set to 0 the T4 timer value will be initialized to a value based on the media type and manual or automatic fax operation. For T.38 the initial value will be 5.12 seconds. For G.711/PSTN the initial value will be 4.5 seconds for manual fax operation and 3.4 seconds for automatic fax operation. If the fax session is the originator and the keyword t4_xmit_timer is in the user configuration file and has a value other than 0 then the T4 timer value will be initialized to the t4_xmit_timer value (limited to 3,000 to 15,000 ms). If the fax session is the answerer and the keyword t4_recv_timer is not in the user configuration file or is set to 0 the T4 timer value will be initialized to a value based on the media type and manual or automatic fax operation. For T.38 the initial value will be 5.12 seconds. For G.711/PSTN the initial value will be 4.5 seconds for manual fax operation and 3.4 seconds for automatic fax operation. If the fax session is the answerer and the keyword t4_recv_timer is in the user configuration file and has a value other than 0 then the T4 timer value will be initialized to the t4_recv_timer value (limited to 3,000 to 15,000 ms). In this mode, the firmware does not do any T4 timer adaptation itself. An event is sent to the host application which informs the host application of the attempt number which just took place, the duration to receive the last response or the T4 timeout value if no response is received, the current value of the T4 timer setting and whether the event is due to a response received or the T4 timer expiring. The host application would could then send an adapted T4 timer value (limited by the firmware to 3,000 to 15,000 ms) for the next command response exchange. The end user application will need to use the existing macro LINE_SET_INCOMING_CMD_FUNC(lp, t4TimerProcessEvent); where the parameter t4TimerProcessEvent is a function which checks if the received event is from the fax facility and has a command specifier indicating it is a FAX_T4_ADAPT_INFO_EVENT. If it is, then the new API function BfvFaxT4TimerParams(lp, &args_fax) can be called, with the new member args_fax.t4TimerValue equal to 0 which indicates to the function that it should obtain the values of the four new members args_fax.t4TimerValue, args_fax.t4Duration, args_fax.t4Attempt and args_fax.t4Timeout. Once these four values have been obtained, the t4TimerProcessEvent(BTLINE *lp, struct args_packet *args) function can calculate a new value for the T4 timer and set args_fax.t4TimerValue equal to this value and then call BfvFaxT4TimerParams(lp, &args_fax) which will send a command to the firmware to set the new T4 timer value.
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- The args_fax structure in the BFV API will be modified with 3 with 4 new fields, t4TimerValue, t4Duration, t4Attempt and t4Attemptt4Timeout.
- A new API function BfvFaxT4TimerParams(MILL_LINE *lp, struct args_fax *args) will be added.
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