Fax T.38 protocol support

Hi team,

How can we enable Fax T.38 protocol, is it support as per Yeti’s documentation?

We tested FAX and it doesn’t seem to work or am is there a config that I need to tick.

Please advice

Tagging @dmitry.s

T.38 is supported and enabled by default.

@dmitry.s

FAX Call From YETI -> FAX Server : NO FAX TONE
FAX Call From Other server -> FAX Server: FAX TONE

I have pasted call logs, unable to find Fax header

2020/12/04 13:06:20.666051 LB:PORT -> SEMS:PORT
INVITE sip:FAX_RECEIVER@LB:PORT;user=phone SIP/2.0
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Via: SIP/2.0/UDP LB;branch=z9hG4bKa7dd.64ce185b3ccb8f8b9911dedbb5cade7c.0
Via: SIP/2.0/UDP CARRIER:PORT;branch=z9hG4bK27dd5a2cd113c05abINV1eb219badf8
Max-Forwards: 34
Contact: <sip:FAX_CALLER@CARRIER:PORT>
To: <sip:FAX_RECEIVER@LB;user=phone>
From: "FAX_CALLER"<sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
CSeq: 357601 INVITE
Allow: INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,INFO
Content-Type: application/sdp
Sup:PORTed: 100rel
User-Agent: UA
Content-Length: 384
X-ORIG-IP: CARRIER
X-ORIG-:PORT: PORT
X-ORIG-PROTO: 1

v=0
o=- 514988474 514988474 IN IP4 CARRIER
s=ENSResip
c=IN IP4 CARRIER_RTP
t=0 0
m=audio 49158 RTP/AVP 8 0 2 4 18 101
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:2 G726-32/8000
a=rtpmap:4 G723/8000
a=rtpmap:18 G729/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:4 bitrate=6.3
a=fmtp:18 annexb=no
a=fmtp:101 0-15
a=silenceSupp:off - - - -
a=sendrecv

2020/12/04 13:06:20.666783 SEMS:PORT -> LB:PORT
SIP/2.0 100 Connecting
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Via: SIP/2.0/UDP LB;branch=z9hG4bKa7dd.64ce185b3ccb8f8b9911dedbb5cade7c.0
Via: SIP/2.0/UDP CARRIER:PORT;branch=z9hG4bK27dd5a2cd113c05abINV1eb219badf8
To: <sip:FAX_RECEIVER@LB;user=phone>
From: "FAX_CALLER"<sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
CSeq: 357601 INVITE
Server: yeti-switch 1.9.20
Content-Length: 0

2020/12/04 13:06:20.819657 SEMS:PORT -> LB:PORT
SIP/2.0 200 OK
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Record-Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Via: SIP/2.0/UDP LB;branch=z9hG4bKa7dd.64ce185b3ccb8f8b9911dedbb5cade7c.0
Via: SIP/2.0/UDP CARRIER:PORT;branch=z9hG4bK27dd5a2cd113c05abINV1eb219badf8
To: <sip:FAX_RECEIVER@LB;user=phone>;tag=12-538B6AF4-5FC9999C000ADC1F-EFAFA700
From: "FAX_CALLER"<sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
CSeq: 357601 INVITE
Server: yeti-switch 1.9.20
Contact: <sip:SEMS:PORT;trans:PORT=udp>
Content-Type: application/sdp
Content-Length: 371

v=0
o=yeti-switch 1607019468 1607019469 IN IP4 103.13.86.58
s=yeti-switch
t=0 0
m=audio 20033 RTP/AVP 0 2 18 101 8 96
c=IN IP4 103.13.86.58
a=rtpmap:0 PCMU/8000
a=rtpmap:2 G726-32/8000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=rtpmap:8 PCMA/8000
a=rtpmap:96 G726-32/8000
a=ptime:20
a=sendrecv

2020/12/04 13:06:20.931207 LB:PORT -> SEMS:PORT
ACK sip:SEMS:PORT SIP/2.0
Via: SIP/2.0/UDP LB;branch=z9hG4bKa7dd.c1687088abdfaa2098bfae300290521a.0
Via: SIP/2.0/UDP CARRIER:PORT;branch=z9hG4bK27dd5a2cd11780b56ACK1eb219badf8
Max-Forwards: 34
To: <sip:FAX_RECEIVER@LB;user=phone>;tag=12-538B6AF4-5FC9999C000ADC1F-EFAFA700
From: "FAX_CALLER"<sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
CSeq: 357601 ACK
User-Agent: UA
Content-Length: 0

2020/12/04 13:06:45.419344 SEMS:PORT -> LB:PORT
BYE sip:FAX_CALLER@CARRIER:PORT SIP/2.0
Via: SIP/2.0/UDP SEMS:PORT;branch=z9hG4bKJuPyRaMK;r:PORT
From: <sip:FAX_RECEIVER@LB;user=phone>;tag=12-538B6AF4-5FC9999C000ADC1F-EFAFA700
To: "FAX_CALLER" <sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
CSeq: 10 BYE
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
Route: <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>, <sip:LB;r2=on;lr;ftag=1eb219ba-co3576-INS002>
Max-Forwards: 70
User-Agent: yeti-switch 1.9.20
Content-Length: 0


2020/12/04 13:06:45.454306 LB:PORT -> SEMS:PORT
SIP/2.0 200 OK
Via: SIP/2.0/UDP SEMS:PORT;received=SEMS;branch=z9hG4bKJuPyRaMK;r:PORT=11000
To: "FAX_CALLER"<sip:FAX_CALLER@CARRIER;user=phone;noa=national>;tag=1eb219ba-co3576-INS002
From: <sip:FAX_RECEIVER@LB;user=phone>;tag=12-538B6AF4-5FC9999C000ADC1F-EFAFA700
Call-ID: 21c-11b5-12319701339-bn06-esy1-0-202.169.177.3
CSeq: 10 BYE
User-Agent: UA
Content-Length: 0

There is no Fax header defined in RFC, why you expect it? Also there is no T.38 negotiation was initiated in SDP, so you have to configure your equipment to negotiate T.38

PS: sign of T.38 negotiation is udptl stream in SDP. It can be present in initial INVITE or negotiated after call connection via re-Invite.

@dmitry.s

Would this explain why there is no Fax tone when calling a fax server from a standard phone?

The interesting observation is that, When I execute call flow is a different scenario, I find different result, for eg:
Senario 1: Mobile phone --> Carrier --> SBC --> FAX : I hear a fax tone on my mobile
Scenario 2: Mobile phone --> Carrier --> Yeti-Switch --> FAX : I hear NO fax tone on my mobile
Scenario 3: Mobile phone --> Carrier --> Yeti-Switch -->SBC --> FAX : I hear a fax tone on my mobile

I guess the yeti-switch requirement is to configure the remote ends with T.38 as Yeti-switch acts as pass-thru only, is that correct?

I’m gathering more logs to verify this…

@dmitry.s Following up on the Fax issue, I have obtained more logs and it appears to me for some reason SEMS isn’t negotiating very well with t38 or something upon negotiated reinvite

From FAX Server to YETI-LB->SEMS_IP.
Sems in responding 488 Not Acceptable Here

2021/02/09 13:04:39.011777 LB_IP:5060 -> SEMS_IP:5065
INVITE sip:SEMS_IP:5065;transport=udp SIP/2.0
Record-Route: <sip:LB_IP;r2=on;lr;ftag=Q56DmUDNjcDrH>
Record-Route: <sip:LB_IP;r2=on;lr;ftag=Q56DmUDNjcDrH>
Via: SIP/2.0/UDP LB_IP;branch=z9hG4bKaf47.f90ec80fe1d4f62ea9da739fb3930072.0
Via: SIP/2.0/UDP FAX_IP:5060;received=FAX_IP;rport=rport;branch=z9hG4bKSymy7ZpXH4Bgm
Max-Forwards: 69
From: "Summit-Fax" <sip:+src_did@FAX_IP>;tag=Q56DmUDNjcDrH
To: <sip:dst_did@LB_IP>;tag=13-27A4DD01-6021EDB300042458-44261700
Call-ID: c27ba0ac9341c9940e8011c4f2bb9166b66d
CSeq: 31864346 INVITE
Contact: <sip:mod_sofia@FAX_IP:5060>
User-Agent: FAX
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
Supported: path, replaces
Content-Type: application/sdp
Content-Length: 318
X-FS-Support: update_display,send_info
Remote-Party-ID: "FAX" <sip:+src_did@FAX_IP>;party=calling;screen=yes;privacy=off

v=0
o=FreeSWITCH 1612809533 1612809535 IN IP4 FAX_IP
s=FreeSWITCH
c=IN IP4 FAX_IP
t=0 0
m=image 26742 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxFillBitRemoval
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:2000
a=T38FaxMaxDatagram:400
a=T38FaxUdpEC:t38UDPRedundancy

Response from SEMS

2021/02/09 13:04:39.013601 SEMS_IP:5065 -> LB_IP:5060
SIP/2.0 488 Not Acceptable Here
Record-Route: <sip:LB_IP;r2=on;lr;ftag=Q56DmUDNjcDrH>
Record-Route: <sip:LB_IP;r2=on;lr;ftag=Q56DmUDNjcDrH>
Via: SIP/2.0/UDP LB_IP;branch=z9hG4bKaf47.f90ec80fe1d4f62ea9da739fb3930072.0
Via: SIP/2.0/UDP FAX_IP:5060;received=FAX_IP;rport=rport;branch=z9hG4bKSymy7ZpXH4Bgm
From: "FAX" <sip:+src_did@FAX_IP>;tag=Q56DmUDNjcDrH
To: <sip:dst_did@LB_IP>;tag=13-27A4DD01-6021EDB300042458-44261700
Call-ID: c27ba0ac9341c9940e8011c4f2bb9166b66d
CSeq: 31864346 INVITE
Server: SEMS 1.9.20
Content-Length: 0

Looks like SEMS received 488 from leg B. Show us LegB signaling.

@dmitry.s Thanks again for your input, much appreciated. I initially thought the same but it looks like SEMS is triggering 488 both ways (to Leg B and to Leg A - both sip trace included below)

LEG B - SEMS → CARRIER

2021/02/10 13:44:36.439517 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
INVITE sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP SEMS_PUB_IP:PORT;branch=z9hG4bKzK.l.aNA;rport
From: "FAX" <sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
To: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
CSeq: 10 INVITE
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
Max-Forwards: 70
X-ORIG-IP: FAX_PUB_IP
X-ORIG-PORT: PORT
X-ORIG-PROTO: 1
User-Agent: Yeti-Switch 1.9.20
Content-Type: application/sdp
Contact: <sip:SEMS_PUB_IP:PORT;transport=udp>
Content-Length: 495

v=0
o=Yeti-Switch 1612908322 1612908323 IN IP4 SEMS_PUB_IP
s=Yeti-Switch
t=0 0
m=audio 25217 RTP/AVP 0 96 97 98 18 101 99 8 100 2 3 102
c=IN IP4 SEMS_PUB_IP
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-16/8000
a=rtpmap:97 iLBC/8000
a=rtpmap:98 G726-32/8000
a=rtpmap:18 G729/8000
a=rtpmap:101 telephone-event/8000
a=rtpmap:99 G726-40/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:100 G726-24/8000
a=rtpmap:2 G721/8000
a=rtpmap:3 GSM/8000
a=rtpmap:102 L16/8000
a=ptime:20
a=sendrecv

2021/02/10 13:44:36.461662 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
SIP/2.0 100 Trying
Via: SIP/2.0/UDP SEMS_PUB_IP:PORT;branch=z9hG4bKzK.l.aNA;rport
To: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
From: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 10 INVITE
Content-Length: 0


2021/02/10 13:44:36.999568 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP SEMS_PUB_IP:PORT;branch=z9hG4bKzK.l.aNA;rport
Contact: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
To: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
From: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 10 INVITE
Allow: INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,INFO
Content-Type: application/sdp
User-Agent: CARRIER_UA
Content-Length: 250

v=0
o=- 24575274 24575274 IN IP4 CARRIER_RTP_IP
s=ENSResip
c=IN IP4 CARRIER_SIG_IP
t=0 0
m=audio 34470 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=silenceSupp:off - - - -
a=sendrecv

2021/02/10 13:44:36.999605 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
SIP/2.0 200 OK
Via: SIP/2.0/UDP SEMS_PUB_IP:PORT;branch=z9hG4bKzK.l.aNA;rport
Contact: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
To: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
From: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 10 INVITE
Allow: INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,INFO
Content-Type: application/sdp
User-Agent: CARRIER_UA
Content-Length: 250

v=0
o=- 24575274 24575274 IN IP4 CARRIER_RTP_IP
s=ENSResip
c=IN IP4 CARRIER_SIG_IP
t=0 0
m=audio 34470 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=silenceSupp:off - - - -
a=sendrecv

2021/02/10 13:44:37.124889 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
ACK sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP SEMS_PUB_IP:PORT;branch=z9hG4bKGvWkya~T;rport
From: "FAX" <sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
To: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
CSeq: 10 ACK
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
Max-Forwards: 70
Contact: <sip:SEMS_PUB_IP:PORT;transport=udp>
Content-Length: 0

2021/02/10 13:44:41.013343 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
INVITE sip:SEMS_PUB_IP:PORT;user=phone SIP/2.0
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28elle7a537INV176fd2a35e9
Max-Forwards: 35
Contact: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380101 INVITE
Allow: INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,INFO,UPDATE
Content-Type: application/sdp
User-Agent: CARRIER_UA
Content-Length: 359

v=0
o=- 24575274 24575275 IN IP4 CARRIER_RTP_IP
s=ENSResip
c=IN IP4 CARRIER_SIG_IP
t=0 0
m=image 36162 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:9600
a=T38FaxMaxBuffer:200
a=T38FaxMaxDatagram:72
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0

2021/02/10 13:44:41.014448 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
SIP/2.0 100 Trying
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28elle7a537INV176fd2a35e9
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380101 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0


2021/02/10 13:44:41.014774 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
SIP/2.0 488 Not Acceptable Here
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28elle7a537INV176fd2a35e9
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380101 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0

2021/02/10 13:44:41.091385 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
ACK sip:SEMS_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28elle7a537INV176fd2a35e9
Max-Forwards: 35
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380101 ACK
User-Agent: CARRIER_UA
Content-Length: 0


2021/02/10 13:44:41.091410 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
INVITE sip:SEMS_PUB_IP:PORT;user=phone SIP/2.0
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28emme7a542INV176fd2a35e9
Max-Forwards: 35
Contact: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380102 INVITE
Allow: INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,INFO,UPDATE
Content-Type: application/sdp
User-Agent: CARRIER_UA
Content-Length: 250

v=0
o=- 24575274 24575276 IN IP4 CARRIER_RTP_IP
s=ENSResip
c=IN IP4 CARRIER_SIG_IP
t=0 0
m=audio 34470 RTP/AVP 8 101
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=silenceSupp:off - - - -
a=sendrecv

2021/02/10 13:44:41.092672 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
SIP/2.0 100 Trying
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28emme7a542INV176fd2a35e9
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380102 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0

2021/02/10 13:44:41.093570 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
SIP/2.0 200 OK
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28emme7a542INV176fd2a35e9
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380102 INVITE
Server: Yeti-Switch 1.9.20
Contact: <sip:SEMS_PUB_IP:PORT;transport=udp>
Content-Type: application/sdp
Content-Length: 267

v=0
o=Yeti-Switch 24575274 24575276 IN IP4 SEMS_PUB_IP
s=Yeti-Switch
c=IN IP4 SEMS_PUB_IP
t=0 0
m=audio 25217 RTP/AVP 101 8
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=rtpmap:8 PCMA/8000
a=ptime:20
a=sendrecv
a=silenceSupp:off - - - -

2021/02/10 13:44:41.164274 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
ACK sip:SEMS_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28emm1cf4a84ACK176fd2a35e9
Max-Forwards: 35
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380102 ACK
User-Agent: CARRIER_UA
Content-Length: 0


2021/02/10 13:45:56.536935 CARRIER_PUB_IP:PORT -> SEMS_PUB_IP:PORT
BYE sip:SEMS_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28enne7a54dBYE176fd2a35e9
Max-Forwards: 35
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380103 BYE
User-Agent: CARRIER_UA
Reason: Q.850 ;cause=16 ;text="Normal call clearing"
Content-Length: 0

2021/02/10 13:45:56.560127 SEMS_PUB_IP:PORT -> CARRIER_PUB_IP:PORT
SIP/2.0 200 OK
Via: SIP/2.0/UDP CARRIER_PUB_IP:PORT;branch=z9hG4bK27dd5a28enne7a54dBYE176fd2a35e9
To: "FAX"<sip:+FAX_SRC_NUM@SEMS_INT_IP>;tag=13-6314AAEA-602348940006AE95-8F9CD700
From: <sip:FAX_DST_NUM@CARRIER_PUB_IP:PORT>;tag=17707e9-co13801-INS002
Call-ID: 13-6201733A-602348940006AE98-8F9CD700
CSeq: 1380103 BYE
Server: Yeti-Switch 1.9.20
Content-Length: 0

LEG A - LB → SEMS

2021/02/10 13:42:23.849536 LB_INT_IP:PORT -> SEMS_INT_IP:PORT
INVITE sip:FAX_DST_NUM@LB_PUB_IP SIP/2.0
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bKa504.50861c55d0ae1fe455ae063bbd0e6512.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKrySKr476051vF
Max-Forwards: 69
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908679 INVITE
Contact: <sip:mod_sofia@FAX_PUB_IP:PORT>
User-Agent: FAX_UA
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
Supported: path, replaces
Allow-Events: talk, hold, conference, presence, as-feature-event, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
Content-Type: application/sdp
Content-Disposition: session
Content-Length: 270
X-FS-Support: update_display,send_info
Remote-Party-ID: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;party=calling;screen=yes;privacy=off
X-ORIG-IP: FAX_PUB_IP
X-ORIG-PORT: RPORT
X-ORIG-PROTO: 1

v=0
o=FreeSWITCH 1612902687 1612902688 IN IP4 FAX_PUB_IP
s=FreeSWITCH
c=IN IP4 FAX_PUB_IP
t=0 0
m=audio 22256 RTP/AVP 0 8 101 13
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=rtpmap:13 CN/8000
a=ptime:20

2021/02/10 13:42:23.850358 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
SIP/2.0 100 Connecting
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bKa504.50861c55d0ae1fe455ae063bbd0e6512.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKrySKr476051vF
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908679 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0

2021/02/10 13:42:24.503681 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
SIP/2.0 183 Session Progress
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bKa504.50861c55d0ae1fe455ae063bbd0e6512.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKrySKr476051vF
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908679 INVITE
Server: Yeti-Switch 1.9.20
Contact: <sip:SEMS_INT_IP:PORT;transport=udp>
Content-Type: application/sdp
Content-Length: 271

v=0
o=Yeti-Switch 1414122446 1414122446 IN IP4 SEMS_PUB_IP
s=Yeti-Switch
t=0 0
m=audio 22273 RTP/AVP 0 101
c=IN IP4 SEMS_PUB_IP
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=sendrecv
a=silenceSupp:off - - - -

2021/02/10 13:42:24.592727 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
SIP/2.0 200 OK
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bKa504.50861c55d0ae1fe455ae063bbd0e6512.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKrySKr476051vF
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908679 INVITE
Server: Yeti-Switch 1.9.20
Contact: <sip:SEMS_INT_IP:PORT;transport=udp>
Content-Type: application/sdp
Content-Length: 271

v=0
o=Yeti-Switch 1414122446 1414122446 IN IP4 SEMS_PUB_IP
s=Yeti-Switch
t=0 0
m=audio 22273 RTP/AVP 0 101
c=IN IP4 SEMS_PUB_IP
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=sendrecv
a=silenceSupp:off - - - -

2021/02/10 13:42:24.596638 LB_INT_IP:PORT -> SEMS_INT_IP:PORT
ACK sip:SEMS_INT_IP:PORT;transport=udp SIP/2.0
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bKa504.06bc36c51d89f99dfc9e019e0649d353.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKS7jctZrayerFB
Max-Forwards: 69
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908679 ACK
Contact: <sip:mod_sofia@FAX_PUB_IP:PORT>
Content-Length: 0


2021/02/10 13:42:26.870228 LB_INT_IP:PORT -> SEMS_INT_IP:PORT
INVITE sip:SEMS_INT_IP:PORT;transport=udp SIP/2.0
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bK5bd4.f0314fefa52064aceba5a4ac8bb0fda7.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKUS5XXNtHr04mj
Max-Forwards: 69
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908680 INVITE
Contact: <sip:mod_sofia@FAX_PUB_IP:PORT>
User-Agent: FAX_UA
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
Supported: path, replaces
Content-Type: application/sdp
Content-Length: 318
X-FS-Support: update_display,send_info
Remote-Party-ID: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;party=calling;screen=yes;privacy=off

v=0
o=FreeSWITCH 1612902687 1612902689 IN IP4 FAX_PUB_IP
s=FreeSWITCH
c=IN IP4 FAX_PUB_IP
t=0 0
m=image 22256 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxFillBitRemoval
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:2000
a=T38FaxMaxDatagram:400
a=T38FaxUdpEC:t38UDPRedundancy

2021/02/10 13:42:26.871571 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
SIP/2.0 100 Trying
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bK5bd4.f0314fefa52064aceba5a4ac8bb0fda7.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKUS5XXNtHr04mj
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908680 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0


2021/02/10 13:42:26.871952 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
SIP/2.0 488 Not Acceptable Here
Record-Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Record-Route: <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bK5bd4.f0314fefa52064aceba5a4ac8bb0fda7.0
Via: SIP/2.0/UDP FAX_PUB_IP:PORT;received=FAX_PUB_IP;rport=RPORT;branch=z9hG4bKUS5XXNtHr04mj
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908680 INVITE
Server: Yeti-Switch 1.9.20
Content-Length: 0


2021/02/10 13:42:26.872465 LB_INT_IP:PORT -> SEMS_INT_IP:PORT
ACK sip:SEMS_INT_IP:PORT;transport=udp SIP/2.0
Via: SIP/2.0/UDP LB_INT_IP;branch=z9hG4bK5bd4.f0314fefa52064aceba5a4ac8bb0fda7.0
Max-Forwards: 69
From: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
To: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 31908680 ACK
Content-Length: 0

2021/02/10 13:43:05.969367 SEMS_INT_IP:PORT -> LB_INT_IP:PORT
BYE sip:mod_sofia@FAX_PUB_IP:PORT SIP/2.0
Via: SIP/2.0/UDP SEMS_INT_IP:PORT;branch=z9hG4bKot~3GaEY;rport
From: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
To: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
CSeq: 10 BYE
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
Route: <sip:LB_INT_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>, <sip:LB_PUB_IP;r2=on;lr;ftag=j7cmmjX9Q9QpF>
Max-Forwards: 70
User-Agent: Yeti-Switch 1.9.20
Content-Length: 0

2021/02/10 13:43:05.989347 LB_INT_IP:PORT -> SEMS_INT_IP:PORT
SIP/2.0 200 OK
Via: SIP/2.0/UDP SEMS_INT_IP:PORT;received=SEMS_INT_IP;branch=z9hG4bKot~3GaEY;rport=RPORT
From: <sip:FAX_DST_NUM@LB_PUB_IP>;tag=12-5E1A106A-6023480F000D4D79-EFAFA700
To: "FAX" <sip:+FAX_SRC_NUM@FAX_PUB_IP>;tag=j7cmmjX9Q9QpF
Call-ID: 0db340408a851be35fdb7f94d2ae8405fab5
CSeq: 10 BYE
User-Agent: FAX_UA
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
Supported: path, replaces
Content-Length: 0

Collect debug sems logs for such calls. This behavior may be caused by gateway configuration.