Why does fax not work reliably over VoIP?
Fax tones are sensitive to packet loss, jitter and codec conversion. T.38 support or an alternative digital document service may be required.
T.38; codec; loss/jitter; ATA/provider.
VoIP/fax provider.
Show the technical detail
On a managed Wi-Fi plan
Keep on wired connection and refer to voice provider features.
On another provider's router
ISP cannot guarantee third-party fax over general internet.
What to be careful of
Avoid changing codecs without provider guidance.
Where this comes from: Official · see the original source ↗ · Draft—technical review · checked 17 August 2026