M3UA
{{SS7stack}}
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 {{IETF RFC|4666}} (which replaces and supersedes {{IETF RFC|3332}}). Like other adaptation protocols, M3UA uses SCTP to transmit messages between its network elements.
Implementation scheme
Image:M3UA-scheme.svg|404x404px|thumb|M3UA: Transmitting MTP-3 messages: on the left is the TDM-network for SS7. On the right is the IP network with SIGTRAN as a transport.|center
rect 1 1 100 72 Point code
rect 1 90 593 123 ISUP
rect 1 123 593 160 SCCP
rect 1 160 100 232 MTP-3
rect 1 232 100 445 MTP-2
rect 1 445 100 515 MTP-1
rect 248 1 347 72 Point code
rect 199 160 296 232 MTP-3
rect 199 232 296 445 MTP-2
rect 199 445 296 515 MTP-1
rect 298 160 397 232 M3UA
rect 298 232 397 302 SCTP
rect 298 302 397 372 IP
rect 298 372 397 445 L2
rect 298 445 397 515 L1
rect 493 1 593 72 Point code
rect 493 160 593 232 M3UA
rect 493 232 593 302 SCTP
rect 493 302 593 372 IP
rect 493 372 593 445 L2
rect 493 445 593 515 L1
rect 15 522 85 565 ISDN
rect 248 522 347 565 Signaling gateway
rect 493 522 580 565 Media Gateway Controller
= 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 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.[http://www.openss7.org/m3ua.html OpenSS7 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[http://wiki.wireshark.org/SampleCaptures?action=AttachFile&do=view&target=isup.cap Wireshark wiki page]).