M3UA is a

communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer science), sem ...

of the SIGTRAN family, used in telephone networks to carry signaling over

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP ...

(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 Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital trans ...

(ATM), which highly improves

scalability Scalability is the property of a system to handle a growing amount of work. One definition for software systems specifies that this may be done by adding resources to the system. In an economic context, a scalable business model implies that ...

of the signaling networks. M3UA stands for MTP Level 3 (MTP3) User Adaptation Layer as defined by the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...

SIGTRAN working group in (which replaces and supersedes ). Like other adaptation protocols, M3UA uses

SCTP The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the ...

to transmit messages between its network elements.

Implementation scheme

Image:M3UA-scheme.svg, 404x404px, 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

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

rect 493 302 593 372 IP rect 493 372 593 445 L2 rect 493 445 593 515 L1 rect 15 522 85 565

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

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.

Wireshark Wireshark is a Free and open-source software, free and open-source packet analyzer. It is used for computer network, network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, ...

is shipped with a dissector for M3UA, sample packets can be found in Wireshark's wiki page, which shows ISUP Packet samples (including M3UAWireshark wiki page
/ref>).

References

{{Reflist Internet protocols Internet Standards Signaling System 7