[asterisk-dev] PJSIP on Asterisk 16 doesn't send t38 packets when sending via res_fax module.

[Steve Sether]

I'm having a lot of trouble getting PJSIP to send a fax via T.38 in 
Asterisk 16.14.1.

 From the pcap, I see the call being made, it connects, RTP goes in both 
directions, the far-end requests a re-invite using t.38, Asterisk sends 
an OK, the OK is acked, and the far ends starts sending t.38 packets, 
asterisk stops sending RTP.

Then Asterisk basically sends nothing else.  No T.38 packets are sent by 
Asterisk, No SIP, nothing.  The far end eventually gives up sending 
t.38, and sends a bye, ending the call.

I'm using a proxy server, and the pjsip.conf looks similar to this:


[proxy-endpoint](!)
type=endpoint
disallow=all
allow=g722
allow=ulaw
allow=alaw
allow=h264
allow=h263p
allow=h263
allow=gsm
context=external
direct_media=no
rtp_symmetric=yes
force_rport=yes
rewrite_contact=yes
rtp_timeout=600
timers=no
timers_min_se=90
timers_sess_expires=90000
callerid=0
trust_id_inbound=yes
trust_id_outbound=yes
send_rpid=yes
send_pai=no
tos_audio=ef
tos_video=af41
t38_udptl=yes
t38_udptl_ec=redundancy
fax_detect=yes

Any help is appreciated.