M3UA defines a protocol for supporting the transport of any SS7 MTP3 user signaling (e.g., ISUP/SCCP messages) over IP using the services of the SCTP. This protocol would be used between an SG and a media gateway controller (MGC) or IP–resident database. M3UA is suitable for transfer messages of any MTP3 user part. The list of these protocol layers includes, but is not limited to, ISUP, SCCP, and telephone user part (TUP). Note: Transaction capabilities application protocol (TCAP) or radio access network application protocol (RANAP) messages are transferred transparently by the M3UA as SCCP payload because they are SCCP user protocols.

The M3UA layer provides the equivalent set of primitives at its upper layer to the MTP3 users as provided by the MTP3 to its local MTP3 users at an SS7 signaling endpoint. In this way, the ISUP and/or SCCP layer aren't aware that the expected MTP3 services are offered remotely from an MTP3 layer at an SG, and not by a local MTP3 layer. The MTP3 layer at an SG may also be unaware that its local users are actually remote user parts over M3UA. In practice, the M3UA extends access to the MTP3 layer services to a remote IP–based application.

Figure 7.

Application Server Process (ASP)—MGC, IP SCP, or IP HLR

Figure 7 depicts an SG containing an instance of the SS7 SCCP protocol layer that may, for example, perform the SCCP global title translation (GTT) function for messages logically addressed to the SG SCCP. If the result of a GTT for an SCCP message yields an SS7 destination point code (DPC) or DPC/subsystem number (SSN) address of an SCCP peer located in the IP domain, the resulting request is sent to the local M3UA for ongoing routing to the final IP destination using the services of SCTP/IP layers.

Figure 8. All–IP architecture

In this example, SCCP messages are exchanged directly between two IP signaling points with resident SCCP user protocol instances, such as RANAP or TCAP. SS7 network interworking is not required; therefore there is no MTP3 network-management status information for the SCCP and SCCP user protocols to consider.