[Freeswitch-users] Freeswitch / FusionPBX T.38 Fax

[Bill Ross]

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 at lists.freeswitch.org [mailto:freeswitch-users-bounces at 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 at 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:  <http://freephoneline.ca/> freephoneline.ca (claims T38 capable)

freeswitch - 1.4.18

x86_64

 

Topology:

 

FS#1:  <http://rossco.org/> rossco.org, using FusionPBX web GUI to send fax

FS#2: <http://rossco.duckdns.org/> 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=  <http://rossco.org/> 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:

$domain=  <http://rossco.duckdns.org/> rossco.duckdns.org

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:

 

Sender( <http://rossco.org/> rossco.org):  <https://pastebin.freeswitch.org/24115> https://pastebin.freeswitch.org/24115

 

Receiver( <http://rossco.duckdns.org/> rossco.duckdns.org):  <https://pastebin.freeswitch.org/24116> https://pastebin.freeswitch.org/24116

 

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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