You would typically have that on the receiver end, not the sender.

On Apr 13, 2015, at 10:41 AM, Bill Ross <rossbcan@gmail.com> wrote:

Thanks Michael;
 
I took your advice and set:
 
fax_enable_t38_request = Not set for the fax receiver (FS#2)
 
Made no difference and, I suspect two things:
 
#1 – May actually be doing T.38 in both cases, fax transaction is using various values for:
 
FLOW T.38T Set rx type 9 and FLOW T.38T Set tx type 9
And, the transaction ends with:
 
FLOW T.38T FAX exchange complete
 
Is this sufficient evidence that T.38 was used? The T.30 packet transfer messages caused me confusion. 
 
#2 – IMHO, the glare condition of both ends setting fax_enable_t38_request = true
Is unavoidable due to lack of signalling / race condition knowledge regarding state of t38_request from the other end.
Strongly suspect since freeswitch has supported T.38 for some time that FS already handles this condition.
Gurus, please weigh in on this.
 
Regards;
Bill Ross
 
From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of Michael Jerris
Sent: April-13-15 9:03 AM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Freeswitch / FusionPBX T.38 Fax
 
you probably don't want to use fax_enable_t38_request = true unless you know for sure that you need it, and you would NEVER want that on both sides.
 
 
On Apr 11, 2015, at 12:04 PM, Bill Ross <rossbcan@gmail.com> wrote:
 
Hi;
 
I am attempting to get T38 Fax working between two FS/FusionPBX installations using mod_spandsp. I am unable to get into T.38 mode, T.30 used, successful fax.
Note that zrtp is disabled for fax calls, due to T38 udpl (not rtp media) incompatibility
Thanks Brian West!: “T.38 Fax takes place over UDPTL, There for it can NOT be encrypted as there was never really a standard for doing so.”
 
Details (both FS’s):
 
SIP Provider: freephoneline.ca (claims T38 capable)
freeswitch - 1.4.18
x86_64
 
Topology:
 
FS#1: rossco.org, using FusionPBX web GUI to send fax
FS#2:rossco.duckdns.org, using spandsp extension to receive fax
 
(spandsp txfax, x1020)FS#1 -> cloud  -> FS#2(spandsp rxfax, x9000)
 
Key variables for fax sender (FS#1), during call:
$domain= rossco.org
Spandsp Fax extension: 1020
t38_passthru = false
zrtp_secure_media = false
fax_enable_t38 = true
fax_enable_t38_request = true
fax_use_ecm = off
inbound-late-negotiation = true
ignore_early_media = false
 
Key variables for fax receiver (FS#2), during call:
Spandsp Fax extension: 9000
t38_passthru = false
zrtp_secure_media = false
fax_enable_t38 = true
fax_enable_t38_request = true
fax_use_ecm = off
inbound-late-negotiation = true
ignore_early_media = false
 
Full Logs w/siptrace:
 
 
 
Note that the SDP’s are correct for T38:
 
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 v=0
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 o=FreeSWITCH 1428750600 1428750602 IN IP4 198.48.238.130
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 s=FreeSWITCH
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 c=IN IP4 198.48.238.130
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 t=0 0
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 m=image 16448 udptl t38
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxVersion:0
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38MaxBitRate:14400
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxFillBitRemoval
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxRateManagement:transferredTCF
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxMaxBuffer:2000
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxMaxDatagram:400
590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxUdpEC:t38UDPRedundancy
 
Questions:
 
1 - According to my interpretation of logs, T38 is not negotiated, despite T38 SDP’s
2 - What am I missing?
 
Thanks;
Bill Ross
 
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