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  • 1.  Faxing

    Posted 4 days ago

    I realize this is a very niche topic but my organization is having an issue related to outbound faxing. My org is BYOC and we use Verizon managed SBCs for our inbound and outbound traffic.

    If you are seeing a decent success rate with outbound faxing, do you know how Verizon set up your SBC's codecs to handle the fax traffic? I know Genesys uses T.30 which everyone, including Verizon, seems surprised about.


    #Telephony

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    Seean Weaver
    MAPFRE USA - Telecom Analyst
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  • 2.  RE: Faxing
    Best Answer

    Posted 3 days ago

    Good Day Seean

    This lines up with a known limitation rather than a config problem you can fully engineer your way around: Genesys Cloud's Edge (and BYOC Cloud media path) only ever negotiates T.30 over G.711 for fax - there's no T.38 relay/gateway support.  I found the following from back in 2019 on the community: "Development looked at industry standards and determined that it was not necessary to support T.38 any longer, so they made a decision to just support T.30 with the PureCloud Edge. - https://community.genesys.com/discussion/t38-faxing
     
    A few things worth pushing on with Verizon, based on similar cases in this community:
     
    Get fax traffic isolated onto its own trunk/DID group with G.711-only, no T.38 offered at all. In another BYOC fax thread here, a contributor noted a case where the customer had to add a diversion header at the SBC specifically to force G.711 for fax calls, since normal codec negotiation was letting it slip to G.729 or triggering a T.38 re-invite that Genesys can't handle.
    Confirm no transcoding is happening on that trunk. T.30 tones are fragile; any transcode hop (even a "harmless" one for voice) will corrupt fax data.
    Check DSCP/EF marking is preserved end-to-end and pull packet captures comparing a successful vs. failed fax - jitter introduced anywhere in the Verizon path will show up as garbled pages or dropped content, usually starting after page 1.
    Some orgs whose fax volume is high enough have ended up routing fax traffic around Genesys Cloud entirely (dedicated ATA/analog gateway or a fax service) rather than fighting the SBC for reliable T.30.
     
    There are also a couple of open Ideas on the Ideas portal asking Genesys to support T.38 instead of/alongside T.30 - worth an upvote if this is impacting you, since it's the actual fix and not something support tuning will resolve:

    https://genesyscloud.ideas.aha.io/ideas/OPTPCM-I-12

    https://genesyscloud.ideas.aha.io/ideas/INB-I-1299

    Hope this helps.

    Regards



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    Stephan Taljaard
    EMBEDIT s.r.o
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