The T.38 protocol was created to provide reliable real-time faxing over IP (FoIP). The original T.30 fax protocol was designed to be implemented over a network that provides relatively smooth and uninterrupted data flows like analog and PRI/T1 lines, and thus does not tolerate the latency, jitter, and packet-loss that are inherent in an IP network. Therefore, the T.38 protocol was created to overcome these challenges. T.38 is not a call setup protocol. This means T.38 devices must use standard call setup protocols like SIP to negotiate the T.38 call. For more details, see the following article: How does T.38 work?