asterisk - pbx
hylafax - provides fax server software
iaxmodem - software modem using the dsp library
the fax path would be like this:
hylafax->iaxmodem->asterisk->sip peer->pstn
there are some tips to improve the successful rate.
1. use g711 codec
- fax transmission just does not favour any lossy codec which inevitably varies the fax tones
2. turn off ECM
- ECM involves data retransmission which could aggravate problems due to network latency and jitter
3. limit transmission rate below 14.4 kpbs can sometimes improve successful rate
4. upgrade your server hardware
- software-based fax transmission is cpu-bound job
5. Add the two lines below to modem configuration files (in /var/spool/hylafax/etc/) to alleviate HDLC problems.
Class1FrameOverhead: 2
Class1SwitchingCmd: "
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