FOIP is more sensitive to packet errors or loss than is VOIP, and FOIP must contain error correction. Information can be repeated in frames, or an error-correcting but delay-adding protocol such as TCP can be used. If one end of the fax session is traditional, there's no way to get true delivery confirmation unless you can complete the message transfer within the limits of the T.30 timers on the sending machine and get the T.30 protocol confirmation.

True FOIP standards

The newer methods encapsulate the T.30/T.4 fax in Simple Mail Transfer Protocol (SMTP), as a Tag Image File Format (TIFF) attachment. SMTP fax can be sent in two ways. Neither real-time or store-and-forward is better; each has advantages and disadvantages in specific applications.

Basic concepts

-- Store and forward -- Store and forward means the faxes are sent whenever an SMTP server delivers them as e-mail messages to the fax-capable router. Real-time means that they are sent one at a time, if and only if there is an active connection between both ends, so that a delivery confirmation can be sent.