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

[Michael Jerris]

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

> On Apr 13, 2015, at 10:41 AM, Bill Ross <rossbcan at 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 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 <mailto: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: freephoneline.ca <http://freephoneline.ca/> (claims T38 capable)
>> freeswitch - 1.4.18
>> x86_64
>>  
>> Topology:
>>  
>> FS#1: rossco.org <http://rossco.org/>, using FusionPBX web GUI to send fax
>> FS#2:rossco.duckdns.org <http://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 <http://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= rossco.duckdns.org <http://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(rossco.org <http://rossco.org/>): https://pastebin.freeswitch.org/24115 <https://pastebin.freeswitch.org/24115>
>>  
>> Receiver(rossco.duckdns.org <http://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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