[asterisk-users] debugging T.38 issues

Tue Oct 14 07:59:01 CDT 2014

Hello list,

We're currently facing some issues concerning T.38 gateway faxing.
This is a device used almost exclusively for receiving faxes. Calls
are incoming to asterisk on a SIP trunk (sangoma netborder) using
G711A. Gateway mode is activated in the asterisk dialplan towards a
Cisco SPA 112 running firmware 1.3.5. We are using asterisk 1.8.13.0
with the T.38 gateway patch applied (I know I know, we should move to
asterisk 11. I'm trying that tonight after business hours).

The issue we're seeing is that faxes incoming from some specific fax
machines consistenly fail. I have indentified 2 types of failures:
- Incoming call is sent to SPA112, reinvite to T.38 is initiated and
accepted. One T.38 packet is sent  from the SPA112 to asterisk
(t30ind: no-signal, see pcap output below) followed by 20 seconds of
nothingness and then the call is hung up.
- Incoming call is sent to SPA112, reinvite to T.38 is initiated and
accepted. A number of T.38 packets is sent from the SPA112 to asterisk
(it repeats NSF,CSI,DIS signals 3 times) followed ba call hangup.

In none of the above 2 cases do I see T.38 packets flowing from
asterisk to the SPA112.

In the logs I see these things that indicate T.38 gateway being started:
[Oct 14 14:16:17] DEBUG[11426] res_fax.c: SIP/SDSD0005-0007cb05 is
attempting to negotiate T.38 but SIP/SOV20001-0007cb04 does not
support it
[Oct 14 14:16:17] DEBUG[11426] res_fax.c: starting T.38 gateway for
T.38 channel SIP/SDSD0005-0007cb05 and G.711 channel
SIP/SOV20001-0007cb04
[Oct 14 14:16:17] DEBUG[11426] res_fax.c: Requesting a new FAX session
from 'Spandsp FAX Driver'.
[Oct 14 14:16:17] DEBUG[11426] res_fax.c: channel
'SIP/SOV20001-0007cb04' using FAX session '660'
[Oct 14 14:16:17] DEBUG[11426] chan_sip.c: T38 state changed to 3 on
channel SIP/SDSD0005-0007cb05

PCAP text output of 1st case:
216.025063 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4877, Time=1179871936
216.042133 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8641, Time=2227760
216.045031 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4878, Time=1179872096
216.062169 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8642, Time=2227920
216.065031 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4879, Time=1179872256
216.082161 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8643, Time=2228080
216.085022 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4880, Time=1179872416
216.102145 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8644, Time=2228240
216.105045 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4881, Time=1179872576
216.122158 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8645, Time=2228400
216.125042 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4882, Time=1179872736
216.142145 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8646, Time=2228560
216.145043 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x6118CC28, Seq=4883, Time=1179872896
216.146259 192.168.196.94 -> 192.168.196.3 SIP/SDP Request: INVITE
sip:0043767079 at 192.168.196.3:5060, with session description
216.147280 192.168.196.3 -> 192.168.196.94 SIP Status: 100 Trying
216.147993 192.168.196.3 -> 192.168.196.94 SIP/SDP Status: 200 OK,
with session description
216.162166 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8647, Time=2228720
216.182149 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8648, Time=2228880
216.187971 28:92:4a:34:19:72 -> ac:f2:c5:35:ed:66 ARP Who has
192.168.196.94?  Tell 192.168.196.3
216.188251 ac:f2:c5:35:ed:66 -> 28:92:4a:34:19:72 ARP 192.168.196.94
is at ac:f2:c5:35:ed:66
216.203946 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x205734A, Seq=8649, Time=2229040
216.229648 192.168.196.94 -> 192.168.196.3 SIP Request: ACK
sip:0043767079 at 192.168.196.3:5060
216.234987 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00000  t30ind: no-signal
237.503971 192.168.196.94 -> 192.168.196.3 SIP Request: BYE
sip:0043767079 at 192.168.196.3:5060
237.505427 192.168.196.3 -> 192.168.196.94 SIP Status: 200 OK

PCAP text output of 2nd case:
116.087359 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x62BD813F, Seq=59490, Time=2244459432
116.094618 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1641, Time=1264160
116.107393 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x62BD813F, Seq=59491, Time=2244459592
116.113615 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1642, Time=1264320
116.127400 192.168.196.3 -> 192.168.196.94 RTP PT=ITU-T G.711 PCMA,
SSRC=0x62BD813F, Seq=59492, Time=2244459752
116.133640 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1643, Time=1264480
116.143569 192.168.196.94 -> 192.168.196.3 SIP/SDP Request: INVITE
sip:0042406282 at 192.168.196.3:5060, with session description
116.144319 192.168.196.3 -> 192.168.196.94 SIP Status: 100 Trying
116.144887 192.168.196.3 -> 192.168.196.94 SIP/SDP Status: 200 OK,
with session description
116.153850 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1644, Time=1264640
116.173646 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1645, Time=1264800
116.199127 192.168.196.94 -> 192.168.196.3 RTP PT=ITU-T G.711 PCMA,
SSRC=0x8EAA59B4, Seq=1646, Time=1264960
116.229940 192.168.196.94 -> 192.168.196.3 SIP Request: ACK
sip:0042406282 at 192.168.196.3:5060
116.237631 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00000  t30ind: no-signal
116.747493 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00001  t30ind: ced
116.757588 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00002  t30ind: no-signal
117.387730 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00003  t30ind: v21-preamble
117.397857 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00003  t30ind: v21-preamble
117.407640 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00003  t30ind: v21-preamble
117.435598 28:92:4a:34:19:72 -> ac:f2:c5:35:ed:66 ARP Who has
192.168.196.94?  Tell 192.168.196.3
117.435899 ac:f2:c5:35:ed:66 -> 28:92:4a:34:19:72 ARP 192.168.196.94
is at ac:f2:c5:35:ed:66
118.677727 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00004  data:v21: hdlc-data[FFC00400006AAA...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: NSF - Non-Standard Facilities)
119.387802 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00005  data:v21: hdlc-data[FFC002CCCC6C2C...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: CSI - Called Subscriber Identification
- Number:042404633)
119.817794 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00006  data:v21: hdlc-data[FFC80104771523...] (HDLC fragment 0)
hdlc-fcs-OK-sig-end (HDLC Reassembled: DIS - Digital Identification
Signal - DSR:ITU-T V.27 ter, V.29, and V.17)
119.877246 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00007  t30ind: no-signal
119.887540 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00008  t30ind: no-signal
123.167804 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00009  t30ind: v21-preamble
123.177713 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00009  t30ind: v21-preamble
123.187801 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00009  t30ind: v21-preamble
124.427832 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00010  data:v21: hdlc-data[FFC00400006AAA...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: NSF - Non-Standard Facilities)
125.127833 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00011  data:v21: hdlc-data[FFC002CCCC6C2C...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: CSI - Called Subscriber Identification
- Number:042404633)
125.567949 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00012  data:v21: hdlc-data[FFC80104771523...] (HDLC fragment 0)
hdlc-fcs-OK-sig-end (HDLC Reassembled: DIS - Digital Identification
Signal - DSR:ITU-T V.27 ter, V.29, and V.17)
125.627325 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00013  t30ind: no-signal
125.637723 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00014  t30ind: no-signal
128.917917 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00015  t30ind: v21-preamble
128.927809 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00015  t30ind: v21-preamble
128.937894 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00015  t30ind: v21-preamble
130.177960 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00016  data:v21: hdlc-data[FFC00400006AAA...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: NSF - Non-Standard Facilities)
130.887932 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00017  data:v21: hdlc-data[FFC002CCCC6C2C...] (HDLC fragment 0)
hdlc-fcs-OK (HDLC Reassembled: CSI - Called Subscriber Identification
- Number:042404633)
131.317940 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00018  data:v21: hdlc-data[FFC80104771523...] (HDLC fragment 0)
hdlc-fcs-OK-sig-end (HDLC Reassembled: DIS - Digital Identification
Signal - DSR:ITU-T V.27 ter, V.29, and V.17)
131.377426 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00019  t30ind: no-signal
131.387773 192.168.196.94 -> 192.168.196.3 T.38 UDP: UDPTLPacket
Seq=00020  t30ind: no-signal
133.914404 ac:f2:c5:35:ed:66 -> 28:92:4a:34:19:72 ARP Who has
192.168.196.3?  Tell 192.168.196.94
133.914427 28:92:4a:34:19:72 -> ac:f2:c5:35:ed:66 ARP 192.168.196.3 is
at 28:92:4a:34:19:72
137.654538 ac:f2:c5:35:ed:66 -> ff:ff:ff:ff:ff:ff ARP Who has
192.168.196.1?  Tell 192.168.196.94
157.053791 192.168.196.94 -> 192.168.196.3 SIP Request: BYE
sip:0042406282 at 192.168.196.3:5060
157.055245 192.168.196.3 -> 192.168.196.94 SIP Status: 200 OK

Is there anyone with expertise or recommendations on this list? Do let
me know if there is any information missing.

Thanks,

Frederic