M3UA

M3UA is a communication protocol of the SIGTRAN family, used in telephone networks to carry signaling over Internet Protocol (IP). M3UA enables the SS7 protocol's User Parts (e.g. ISUP, SCCP and TUP) to run over virtually any network technology breaking its limitation to telephony equipment like T-carrier, E-carrier or Asynchronous Transfer Mode (ATM), which highly improves scalability of the signaling networks.

M3UA stands for MTP Level 3 (MTP3) User Adaptation Layer as defined by the IETF SIGTRAN working group in (which replaces and supersedes ). Like other adaptation protocols, M3UA uses SCTP to transmit messages between its network elements.

Typical scheme
________                  _________                __________   MTP3 point-code                        common point-code PC1                                   PC2
 * |                  |       |                |     MGC|
 * SP |<->|  SGW  |<---|-->(AS) |
 * ______|  SS7 network     |_______|   IP network   |________|

Use SGW as STP
Several AS owns PC itself and uses SGW as STP (transit pointcode). ________                _____________               ___________   MTP3                    point-code point-code                  PC2 PC1
 * |                |    SGW    |               |      MGC|
 * |                |           | /-|-->(AS)  | point-code PC3
 * SP |<|-->(STP)<--|-              |         |
 * |                |           | \-|-->(AS)  | point-code PC4
 * ______| SS7 network    |___________|   IP network  |_________|

Protocol
M3UA uses a complex state machine to manage and indicate states it's running. Several M3UA messages are mandatory to make an M3UA association or peering fully functional (ASP UP, ASP UP Acknowledge, ASP Active, ASP Active Acknowledge), some others are recommended (Notify, Destination Audits (DAUD)).

Additional info
An open implementation of the M3UA standard can be found at OpenSS7's web site.

Wireshark is shipped with a dissector for M3UA, sample packets can be found in Wireshark's wiki page, which shows ISUP Packet samples (including M3UA ).