hello every body

i have problem in receiving fax from e1 lines. this is my scenario:

faxphone—-ericson pbx —e1—-asterisk—-sip—–zoiper-softphone

when i send fax from zoiper, i can receive it successfully on the faxphone but when i send fax from faxphone, i can not receive it on zoiper. i want do this just by using faxdetect option. when fax comes from faxphone, chan dahdi on asterisk detect fax and redirect to fax extension. in fax extension, i just dial sip peer which is connected to zoiper like this:

exten=>fax,1,Dial(SIP/peer-1/${EXTEN})

peer-1 is a sip peer which is defined in sip.conf like this:

[peer-1]
host2.168.0.XX
type=peer context=from-trunk insecure=port,invite

i set debug messages and understand that sip channel can not identify fax and try to send it like a voice call (set rtp and other things exact a voice call). what is the problem? does chan dahdi should send something for sip to identify fax session? or something is wrong related to chan sip?
i struggle a lot but can not solve this problem. any comments or hints are really appreciated.

SAM