Fax service with Telnyx (via T.38 or G711)

Publisher

Telnyx

URL

https://support.telnyx.com/en/articles/1130672-fax-service-with-telnyx-via-t-38-or-g711

Published

unknown

Updated

unknown

Accessed

2026-10-02

HTTP status

200

License

Telnyx proprietary; no-redistribution; short excerpts and locators only

Source notes citing this source

• Which side sends the T.38 re-INVITE differs by carrier and direction (Bandwidth expects a customer re-INVITE; Telnyx defaults to sending it on outbound and expects the customer to send it on inbound), so a re-INVITE-side mismatch is a plausible cause of calls that never leave G.711. inferred in context
• Telnyx recommends disabling ECM on the fax machine and setting the baud rate to 9600 or below for faxing over its network. in context
• For inbound faxes, Telnyx expects the customer side to send the T.38 re-INVITE; unchecking Enable T38 FAX gateway makes Telnyx refuse T.38 re-INVITEs so the call stays on G.711. in context
• For outbound faxes, Telnyx by default sends the T.38 re-INVITE itself once fax tone is detected; the initiator can be set to Telnyx, Customer, or Disabled. in context

Cite this source record

APA

WarmTransfer. (2026, October 2). Fax service with Telnyx (via T.38 or G711). WarmTransfer. https://warmtransfer.net/knowledge/sources/telnyx-support-fax-t38-g711

BibTeX

@misc{warmtransfer-telnyx-support-fax-t38-g711,
  title  = {Fax service with Telnyx (via T.38 or G711)},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/sources/telnyx-support-fax-t38-g711},
  note   = {Telnyx, accessed 2026-10-02}
}