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.
| SS7 protocols by OSI layer | |
| Application | INAP, MAP, IS-41... TCAP, CAP, ISUP, ... |
|---|---|
| Network | MTP Level 3 + SCCP |
| Data link | MTP Level 2 |
| Physical | MTP Level 1 |
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). Like other adaptation protocols, M3UA uses service of SCTP to transmit messages between its network elements.
Implementation scheme
Typical scheme
________ _________ __________ | | | | | MGC| | SP |<----------------->| SGW |<---------------|-->(AS) | |______| SS7 network |_______| IP network |________| MTP3 point-code common point-code PC1 PC2
Use SGW as STP
Several AS owns PC itself and uses SGW as STP (transit pointcode).
________ _____________ ___________ | | | SGW | | MGC| | | | | /-------------|-->(AS) | point-code PC3 | SP |<----------------|-->(STP)<--|- | | | | | | \-------------|-->(AS) | point-code PC4 |______| SS7 network |___________| IP network |_________| MTP3 point-code point-code PC2 PC1
Protocol
M3UA uses a complex state machine to manage and indicate states it's running. Several M3UA messages are mandatory to make a 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.[1]
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[2]).