T.38 is a telecommunications protocol that was developed specifically to handle fax signals over internet-based connections. If you have encountered reliability problems with fax over VoIP, or if you are evaluating enterprise fax solutions and want to understand why some perform better than others over IP networks, T.38 is worth understanding.
The Problem T.38 Was Designed to Solve
Traditional fax works over analog phone lines by converting a document into audio tones and transmitting those tones through the Public Switched Telephone Network. Analog lines are circuit-switched, which means a continuous, dedicated connection carries the signal for the entire duration of the transmission. That consistency is why traditional fax is reliable.
Internet connections are packet-switched. Data travels in packets that may take different routes, arrive slightly out of order, or be delayed by congestion. For most internet applications, that does not matter because the receiving software buffers and reassembles packets with enough tolerance to handle small variations. Voice calls handle it reasonably well because human ears can compensate for brief interruptions.
Fax signals cannot. The audio tones that carry fax data are exquisitely sensitive to the timing variations, packet loss, and jitter that packet-switched networks produce. A fax signal transmitted over a standard VoIP connection using the G.711 voice codec will fail or degrade far more often than most organizations find acceptable.
T.38 was developed to solve this by creating a protocol specifically designed for fax over IP. Rather than trying to pass fax audio tones through a network that was not built for them, T.38 converts the fax signal into a redundant data stream that can tolerate the packet loss and timing variations of IP networks. Redundancy in the data stream means that individual lost packets can be reconstructed, which significantly improves reliability over what standard VoIP fax can achieve.
How Lane Uses T.38
Lane has partnered with T38Fax as part of the Passport ecosystem, with T38Fax’s Power-T.38 gateway interoperating with Passport’s fax components. That partnership is documented on Lane’s partners page, and it reflects Lane’s commitment to building fax reliability on protocols that were designed for the job.
The etherFAX network that underlies Fax 2.0 and Passport’s cloud transmission uses Time Division Multiplexing (TDM) for fax connectivity, which provides the dedicated, consistent signal path that fax requires. For organizations whose fax traffic passes through IP networks, the combination of T.38 protocol support and etherFAX’s network architecture delivers the kind of reliability that standard VoIP-based cloud fax cannot consistently achieve.
What This Means When Evaluating Fax Solutions
When a cloud fax vendor tells you their solution is reliable over VoIP, it is worth asking specifically how they handle fax-over-IP reliability. Solutions that use T.38 are built to handle the characteristics of IP networks for fax. Solutions that rely on G.711, the standard voice codec, are using a protocol designed for voice and hoping fax will survive the same conditions.
For organizations in healthcare, legal, or financial services where a failed transmission has compliance or operational consequences, the protocol question is not academic. The FAQ Friday post on fax security and privacy covers the security layer of enterprise fax. The reliability layer starts with the protocol.
Contact Lane if you want to discuss fax reliability in the context of your specific network environment.
