Asterisk 1.6+DigiumFax 1.6 Не приходит от некоторых абонентов

Факс настроен и работает только на прием. Почему-то с некоторых телефонов не приходит факс. Люди дозваниваются, но потом идет обрыв.

в файле sip.conf присутсвует:

[general]

t38pt_udptl=yes

файл exstension.conf:

[main]

exten => 6000,n,Dial(Local/fax@grouprittalsoftfax_receive)
exten => 6000,n,Hangup()

[grouprittalsoftfaxreceive]
exten => fax,1,NoOp(grouprittalsoftfax from ${CALLERID(NUM)})
exten => fax,n,Set(GLOBAL(FAXCOUNT)=${IF($["${GLOBAL(FAXCOUNT)}"=""]?0:${GLOBAL(FAXCOUNT)})})
exten => fax,n,Set(GLOBAL(FAXCOUNT)=$[${GLOBAL(FAXCOUNT)}+1])
exten => fax,n,Set(FAXCOUNT=${GLOBAL(FAXCOUNT)})
exten => fax,n,Set(FAXFILE=/tmp/faxes/${FAXCOUNT}-from${CALLERID(NUM)}.tif)
exten => fax,n,ReceiveFax(${FAXFILE})
exten => fax,n,Hangup()

Перенаправление на сервер Asterisk происходит так:

fax protocol t38 ls-redundancy 5 hs-redundancy 2 fallback pass-through g711ulaw
no vad

Лог fax debug:

VERBOSE[23457] pbx.c: -- Executing [fax@grouprittalsoftfaxreceive:6] ReceiveFAX("Local/fax@grouprittalsoftfaxreceive-b7a8;2", "/tmp/faxes/fax.tif") in new stack
VERBOSE[23457] resfax.c: -- Channel 'Local/fax@grouprittalsoftfaxreceive-b7a8;2' receiving FAX '/tmp/faxes/fax.tif'
VERBOSE[23456] appdial.c: -- Local/fax@grouprittalsoftfaxreceive-b7a8;1 answered SIP/x.x.x.x-00001677
VERBOSE[23457] resfaxdigium.c: -- Channel 'Local/fax@grouprittalsoftfaxreceive-b7a8;2' FAX session '50' started
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 000.000074 ], STATEVTSTRTRX st: IDLE rt: IDLENSRX
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 000.000141 ], STATEVTRXHWRDY st: WTRXHWRDY rt: RRDYNHRY
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 000.000174 ], P30EVNRECEIVESTARTED
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 000.000194 ], STATINFOCSI
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 000.000237 ], STATINFODIS
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 005.247534 ], STATEVTTXV21DONE st: WTDISRSP rt: WDSRNT21
VERBOSE[23456] pbx.c: == Spawn extension (default, 6000, 2) exited non-zero on 'SIP/x.x.x.x-00001677'
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 006.285028 ], STATEVTTMRINTEXP st: WTDISRSP rt: XXXXNTIX
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 008.491609 ], STATEVTT4EXP st: WTHWCLS rt: UNEXPECT
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 008.787449 ], STATEVTHWCLOSE st: WTHWCLS rt: WCLSNCLS
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 008.787526 ], STATSESCOMPLETE
VERBOSE[23459] resfaxdigium.c: -- FAX handle 0: [ 008.787557 ], P30EVNCOMPLETE
ERROR[23457] resfax.c: channel 'Local/fax@grouprittalsoftfaxreceive-b7a8;2' FAX session '50' failure, reason: 'fax session timed-out' (TIMEOUT)

В чем может быть проблема? И в какую сторону копать? Вообще понять не могу. Пробовал в extension.conf добавить Ringing(), не помагает:

exten => 6000,1,Ringing()
exten => 6000,n,Dial(Local/fax@grouprittalsoftfax_receive)
exten => 6000,n,Hangup()