M3UA

M3UA, or MTP3 User Adaptation Layer, is a signaling protocol used in the SIGTRAN framework to transport SS7 MTP3 user messages over IP networks. It was developed by the IETF SIGTRAN Working Group and is defined to carry MTP3 User signaling over the SCTP transport. M3UA provides the mapping and control needed to convey SS7 MTP3 data between IP-based signaling points while preserving the semantics of the MTP3 layer.

In operation, M3UA introduces the concepts of Application Server (AS) and Application Server Process (ASP). An ASP connects to an AS over SCTP, forming a signaling association that carries MTP3 user data. The protocol defines control and data messages for ASP state management, route and destination handling, and the delivery of MTP3 messages. Routing keys and destinations are used to direct MTP3 traffic to the appropriate network element or application.

M3UA runs on top of SCTP, leveraging SCTP features such as reliable delivery, multi-homing, and multi-stream transport to support signaling traffic. It supports multiple associations between endpoints to enable redundancy and load sharing, which is important for mission-critical SS7 signaling. Typical deployments involve Signaling Gateways or interfaces between SGs, STPs, and application servers to extend SS7 signaling across IP backbones.

Standardization and usage: M3UA is specified in RFC 4666 within the SIGTRAN family of protocols, alongside related mechanisms for signaling transport over IP. It is widely used in telecom networks to interconnect SS7 signaling over IP networks, enabling services such as call setup, routing, and network management across IP domains. See also related SIGTRAN protocols like M2UA and SUA.