This appears to be the latest protocol for faxing via phone ("general switched telephone") vs. OIP. I don't get why you'd fax via the net, however. Attach it, right?

Anyhow... T.30๏ฟฝ:๏ฟฝProcedures for document facsimile transmission in the general switched telephone network:

Recommendation T.30 (09/05)
Approved in 2005-09
Status : In force