Bandwidth T.38 faxing support guide

Publisher

Bandwidth Inc.

URL

https://www.bandwidth.com/support/en/articles/12822959-bandwidth-t-38-faxing-support-guide

Published

2025-11-17

Updated

unknown

Accessed

2026-10-02

HTTP status

200

License

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

Source notes citing this source

• Bandwidth states that if the T.38 re-INVITE is unsuccessful a SIP 488 Not Acceptable Here is sent and transmission should fall back to G.711. in context
• Bandwidth's T.38 service requires the call to be set up as a G.711 VoIP call, followed by a customer re-INVITE to T.38 that must be offered and accepted. in context
• For G.711 faxing, Bandwidth says ECM is not supported and speeds are limited to 9600 or 14.4k, and recommends setting the fax machine to its lowest baud rate with error correction mode off. in context
• Bandwidth recommends setting the T.38 MaxDatagram to 176. in context
• Bandwidth states that fax will not work over compressed codecs and recommends uncompressed G.711u for G.711 faxing. in context
• Bandwidth offers no SLA or guarantee on fax performance parameters and does not support troubleshooting deep into RTP or UDPTL data. in context

Cite this source record

APA

WarmTransfer. (2025, November 17). Bandwidth T.38 faxing support guide. WarmTransfer. https://warmtransfer.net/knowledge/sources/bandwidth-support-t38-faxing-guide

BibTeX

@misc{warmtransfer-bandwidth-support-t38-faxing-guide,
  title  = {Bandwidth T.38 faxing support guide},
  author = {{WarmTransfer}},
  year   = {2025},
  url    = {https://warmtransfer.net/knowledge/sources/bandwidth-support-t38-faxing-guide},
  note   = {Bandwidth Inc., accessed 2026-10-02}
}