vFax and T.38

2talk vFax replaces a physical fax machine by using email and the 2talk fax gateway to send and receive faxes. Inbound faxes are delivered by email, and outbound faxes are sent by emailing an attachment to the fax gateway.

If your organization operates an emergency medical facility or requires guaranteed fax delivery for critical workflows, do not rely on vFax as the only transmission method. Fax delivery can still be affected by the destination fax machine, carrier routing, document format, and network conditions.

Why fax over IP is different

Traditional fax machines expect a continuous, reliable connection. Voice over IP networks can introduce packet loss, jitter, or timing changes, and fax machines are less tolerant of those problems than normal voice calls.

T.38 is a fax-over-IP protocol designed to make fax transmission more reliable by allowing fax gateways to handle retransmission and buffering. With vFax, the 2talk fax gateway handles the fax session while you send and receive documents by email.

Cloud PBX fax numbers

Dedicated 2talk fax numbers use T.38 through the fax gateway. If you port an existing fax number to 2talk, contact support to have the number configured as a fax line.

Known issues

These scenarios can cause fax failures or unreliable delivery:

1. Machine-to-machine faxing: vFax is designed for email-to-fax and fax-to-email delivery. Direct fax-machine-to-fax-machine calls may bypass the email workflow and reduce the reliability benefits of the fax gateway.
2. Dual answer or fax mode: Some devices that auto-answer in mixed voice/fax mode can cause the fax gateway to treat the call as voice and disconnect.
3. High-speed fax machines: Fax gateways may request a lower baud rate, commonly 9600, to improve reliability. Devices that cannot adjust speed may fail more often.
4. Color faxing: vFax is intended for standard black-and-white fax documents. Color faxing is not supported.