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Tuning the configuration - some values may need to be tuned depending on the performance of the fax server.
Initially, it is recommended to start with default parameters values and assess the performance of the fax server. You should start out with default values for both btcall.cfg and callctrl.cfg (with the exception of the sip_default_gateway and sip_Contact fields in callctrl.cfg).
Leave t4_xmit_timer at its default value. This can be done by commenting out the line completely in the btcall.cfg file. To comment out any parameter in the btcall.cfg file, simply put the # in front of that parameter.
Keep media_renegotiate_delay_outbound to -1 in callctrl.cfg This parameter is set so that the media gateway will send the T.38 re-INVITE when the SR140 places an outbound call. The user should assess the fax server performance using T.38, which is the standard for FoIP. If the fax call success rate is lower than expected, then the user can try using G.711 pass-through as a second choice.
Further tuning of configuration – if an issue is observed, further adjustments may need to be made based on the log analysis. It is strongly recommended to change one parameter at a time and determine if doing so has resolved the particular issue. It is best to consult with the Dialogic technical support team on making parameter changes. Some typical scenarios and adjustments that may need to be made include (but are not necessarily limited to):
If there is no response to outgoing fax control messages, then the "t4_xmit_timer" parameter could be extended. The T4 timer will expire if a fax end point does not receive a response message to an outgoing command. When that happens, the fax device will re-send its command and again wait for a response. If still no response arrives, the device will send the command one more time and then hang up if again there is no response. This will result in Brooktrout hangup codes such as "MPS sent three times with no response" or "PPS-EOP sent three times with no response". It is recommended to start with with 8000 (ms) and make small increments to "t4_xmit_timer" parameter and to gauge performance and see if the issue has been addressed.
If error correction mode (ECM) is not used, then MR compression may be decided upon for the fax session negotiation. However, while some end points advertise MR support, the end points might not adequately support this and fax transmission failures may be observed. If you suspect the end point might not adequately support MR compression, then try setting "line_compression" to 0 to use MH compression instead.
If fax server performance issues are still observed despite previous adjustementsadjustments, then try setting the fax_transport_protocol to "t38_never" to try G.711 pass-through. G.711 fax pass-through is also supported by the Brooktrout SR140 software if you running an R3 License. If you are not using an R3 license, then an upgrade to R3 is needed to include G711 pass-through support. While more susceptible to possible IP network issues, G.711 fax pass-through provides an option for enabling FoIP when T.38 is not supported, or when the IP network meets the requirements for successful fax transport using G.711.
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If the site has an existing Brooktrout Fax Board - please obtain a recording from the setup. The audio file will be used by the Dialogic technical support team to understand the audio levels that are present on the line and if further adjustments might be necessary.
The fax application being used may have the capabilities to record the audio file. Please check with your fax ISV.
This article also has attached a sample application that can be used to gather the recording. The sample recording application is called voicermd.c,
, and can be used on channels 2 and 3 to record the inbound and outbound streams.View file name 4128_voicermd.zip The parameter "debug_control 1 3" would need to be added into btcall.cfg to turn on the recording feature; Dialogic technical support can assist with using this feature.
SR140 Log Collection -when troubleshooting, the following logs always needs to be gathered. It is important to collect all the various logs together. If logs are collected from different time frames, they will not assist in isolating the issue being examined.
Debug log – channel information needs to be included in the log, e.g., "[41,2]", "[41,3]", … etc. If a debug log has only Admin channel information, i.e. "[41,1]", then it would not be of value in isolating an issue.
ECC log - make sure to use a full path name for the "trace_file" parameter in callctrl.cfg and also make sure that the Bostsrv service points to the same btcall as the one that the application uses when it calls BfvLineReset. This will make sure that all of the call control information will appear in the ECC log, most importantly the SIP messages.
Wireshark - traces should be gathered from the SR140 and DMG1000 or DMG2000 points. This will help in analyzing the call flow and information flowing through the network.
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