[Freeswitch-users] Freeswitch / FusionPBX faxback <-> faxback extensions T.38 Fax FAIL: Ack Time Out

[Bill Ross]

Hi;

 

Faxback Support - SUP-00019595

 

I am attempting to get T38 Fax working between two FS/FusionPBX
installations using faxback VOIP plugin extensions. The fax TX (FS#1)
endpoint drops the call due to "Ack Timeout" after two pages.

 

Faxback VoIP client plugin:

 

http://www.faxback.com/Products/FreeMSFaxDownload.aspx

 

I am able to successfully receive a fax using this faxback endpoint if
transmitted by FS/spandsp.

 

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 faxback plugin (x1019)  to send fax

FS#2:rossco.duckdns.org, using faxback plugin (x1019) to receive fax

 

(faxback x1019)FS#1 -> cloud  -> FS#2(faxback x1019)

 

Key variables for fax sender (FS#1), during call:

$domain= rossco.org

Faxback Fax extension: 1019

t38_passthru = true

zrtp_secure_media = false

fax_enable_t38 = false (not set)

fax_enable_t38_request = false (not set)

fax_use_ecm = off (not set)

inbound-late-negotiation = true

ignore_early_media = true

 

Key variables for fax receiver (FS#2), during call:

$domain= rossco.duckdns.org

Faxback Fax extension: 1019

t38_passthru = true

zrtp_secure_media = false

fax_enable_t38 = false (not set)

fax_enable_t38_request = false (not set)

fax_use_ecm = false (not set)

inbound-late-negotiation = true

ignore_early_media = false

 

Full Logs w/siptrace:

 

Sender(rossco.org): https://pastebin.freeswitch.org/24117

 

Receiver(rossco.duckdns.org): https://pastebin.freeswitch.org/24118

 

Note that the SDP's are correct for T38:

 

   v=0

   o=Sippy 177245968 2 IN IP4 208.65.240.165

   s=FreeSWITCH

   t=0 0

   m=image 49714 udptl t38

   c=IN IP4 208.65.240.165

   a=T38FaxVersion:0

   a=T38MaxBitRate:14400

   a=T38FaxRateManagement:transferredTCF

   a=T38FaxMaxBuffer:200

   a=T38FaxMaxDatagram:72

   a=T38FaxUdpEC:t38UDPRedundancy

 

Questions:

 

1 - According to my interpretation of logs, T38 and t38_passthru is
negotiated

2 - I do not have the expertise (yet) to determine the reason for "Ack
Timeout"

2 - What am I missing?

 

Thanks;

Bill Ross

 

 

 

 

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