Not possible since t.38 doent take place over RTP! On Sunday, March 22, 2015, Bill Ross <rossbcan@gmail.com> wrote:
Folks;
I am attempting to deploy T.38 Fax (ZRTP Secure) with FreeSwitch / FusionPBX and am seeking system architectural advice regarding how to approach this.
Question #1: Recommended T.38 capable ATA (and settings) for reliable FAX.
Approach #1 ZRTP mitm with T.38 SIP Extension (either T.38 capable ATA or soft endpoint) – preferred approach
T.38 SIP endpoint <-> FS#1 / mitm <-> cloud <-> FS#2 mitm <-> T.38 SIP endpoint
I am using a soft T.38 SIP endpoint, plugin for Windows Fax and Scan from faxback, available here:
http://www.faxback.com/Products/Trialware.aspx?NET_SAT_EDITION=Small%20Busin...
SIP Gateway, just prior to bridge:
*<action application="export" data="fax_enable_t38_request=true"/>* *<action application="set" data="execute_on_answer=t38_gateway peer"/>*
*Extension, just prior to bridge:*
*<action application="set" data="fax_enable_t38_request=true"/>* *<action application="set" data="execute_on_answer=t38_gateway self"/>*
*What I am seeing (two FS systems), each with T.38 soft extensions, attempting to fax each other.*
* ZRTP negotiation fails (Max retransmissions fail) -> NOZRTP*
* ONE SDP is T38Fax (extension or gateway), Other is PCMU/8000*
* The extension of T.38 enters state [ready] and immediately hangs up, I assume from SDP mismatch*
Question #2: Anyone successfully done this, if so, how?
Question #3: Is what I am attempting architecturally possible? Can T.38 be mitm’d?
Question #4: If so, advice regarding how to debug the ZRTP negotiation failure and SDP negotiation failure.
Approach #2: FS terminates incoming T.38 fax, stores and forwards to fax extension, FS terminates outgoing T.38 fax, stores and forwards to SIP gateway to final destination.
T.38 SIP endpoint <-> FS#1 / terminate fax <-> FS#1 forward fax <-> cloud <-> FS#2 / terminate fax <-> FS#2 forward fax <-> T.38 SIP endpoint
Question #5: Will this work? Anyone done it, how? ZRTP gotcha’s?
Thanks;
Bill
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