High Quality Content by WIKIPEDIA articles! M3UA stands for MTP Level 3 (MTP3) User Adaptation Layer as defined by the IETF SIGTRAN working group in RFC 4666 (which replaces and supersedes RFC 3332). M3UA enables the SS7 protocol`s User Parts (e.g. ISUP, SCCP and TUP) to run over IP instead of telephony equipment like ISDN and PSTN. It is recommended to use the services of SCTP to transmit M3UA.