FoIP

FoIP, short for Fax over IP, is the transmission of traditional fax documents over IP-based networks. It allows fax workflows to operate over corporate Ethernet, VPNs, or the public Internet by using a fax gateway, an IP-PBX, or a fax server to bridge IP networks with the legacy PSTN or with other VoIP endpoints. FoIP deployments typically rely on one of two approaches: ITU-T T.38 fax relay and G.711-based fax pass-through. T.38 encodes fax data as IP packets and is designed to be robust over packet-switched networks, while pass-through sends the fax tones as ordinary audio over the IP stream, relying on the modem at the receiving end to interpret the data.

In operation, T.38 negotiates fax parameters between endpoints and can retransmit lost packets, improving reliability in networks with jitter or occasional loss. Pass-through can require more careful network tuning and may be more sensitive to timing variations, but it can be compatible with older devices that do not support T.38.

Standards and interoperability: T.38 is defined by ITU-T Recommendation T.38 and is widely implemented in enterprise VoIP systems, gateways, and fax servers. Interoperability depends on vendor support and correct configuration. Many deployments combine FoIP with traditional dial plans via gateways to ensure recipients on PSTN can receive faxes issued from IP networks.

Security and administration: FoIP signaling usually traverses TLS, and media streams may be protected with SRTP where available. Compliance considerations include ensuring proper archiving of received faxes and protecting sensitive content during transport. Benefits of FoIP include reduced telephone line usage, simplified administration, and potential for centralized fax management; drawbacks include potential reliability issues in poorly conditioned networks and added gateway complexity.