The V.150.1 protocol is an ITU-T recommendation for the transmission of modem data over IP networks. This protocol is the preferred industry-standard modem relay protocol. SIP trunks support the V.150.1 Modem Relay mode. In the V.150.1 Modem Relay mode, modem features are implemented according to ITU-T V-series recommendations. These recommendations are used for interoperation with the non-Avaya trunk-side and line-side modem equipments, and with native-V.150.1 secure IP endpoints. This mode uses the V.150.1 protocol that defines how to send modem traffic between modems and telephone devices over an IP network. This mode also supports Modem-over-IP interoperability with SIP endpoints and third-party SIP gateways. This mode uses the Simple Packet Relay Transport (SPRT) protocol to send data between V.150.1–capable endpoints.