M3UA

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SS7 protocol suite
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 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.

Contents

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 SCTP to transmit messages between its network elements.

Implementation scheme

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. M3UA-scheme.svgISUPSCCPMTP-3MTP-2MTP-1MTP-3MTP-2MTP-1IPL2L1IPL2L1
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.

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. [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] ).

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References