T.38 is a telecommunications protocol 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 platforms perform more reliably than others, 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, meaning a continuous, dedicated connection carries the signal for the entire duration of the transmission. That consistency is why traditional fax is reliable when the hardware and lines are in good condition.
Internet connections are packet-switched. Data travels in packets that may take different routes, arrive slightly out of order, or be delayed by network congestion. For most internet applications that variation does not matter because the receiving software buffers and reassembles packets with enough tolerance to handle small timing differences. Voice calls manage it reasonably well because human ears can compensate for brief interruptions.
Fax signals cannot. The audio tones that carry fax data are 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 in a business-critical workflow.
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 built for voice, T.38 converts the fax signal into a redundant data stream that can tolerate the packet loss and timing variations of IP networks. The redundancy in that data stream means 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 reflected on Lane’s partners page and represents Lane’s commitment to building fax reliability on protocols that were purpose-built for fax transmission rather than adapted from voice infrastructure.
The etherFAX network that underlies Fax 2.0 and Passport’s cloud transmission uses Time Division Multiplexing 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 reliability that standard VoIP-based cloud fax cannot consistently achieve.
What This Means When You Are 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 applying it to a use case with fundamentally different signal requirements.
For organizations in healthcare, legal, or financial services where a failed transmission carries compliance or patient safety consequences, that protocol distinction is not abstract. A fax platform built on T.38 handles the variability of IP networks by design. One built on G.711 handles it by hoping the network is stable enough that fax signals survive.
The reliability of any fax platform ultimately depends on both the protocol layer and the network infrastructure it runs on. Passport’s architecture addresses both, which is why Lane customers operating in high-volume, compliance-sensitive environments experience the transmission reliability their workflows require.
If you want to discuss fax reliability in the context of your specific network environment, contact Lane or schedule a strategy call with the team.
