What is T.38?

T.38 is an internationally recognized protocol designed specifically for the reliable transmission of fax messages in real-time over an IP network. It is the core technology that powers Fax over IP (FoIP).

Traditional fax machines communicate using analog signals that are extremely sensitive to network delays and packet loss, which are common on the internet. Simply trying to send a fax as a standard audio stream (like a VoIP call) is highly unreliable and often results in failed transmissions.

The T.38 protocol solves this problem. It works by converting the analog fax signals into a special image-based data format that is optimized for IP networks. This process includes error correction mechanisms that make the transmission far more resilient to network imperfections like latency and jitter.

When a fax is sent using T.38, the data is intelligently packaged and transported across the IP network and then reassembled on the other side, ensuring the document arrives intact. T.38 is the standard protocol used by most VoIP gateways, Analog Telephone Adapters (ATAs), and cloud fax services to ensure that faxing can continue to function dependably in a modern, digital communications environment.