M3UA (MTP Level 3 User Adaptation Layer) Protocol

M3UA seamlessly transports SS7 MTP3 user part signaling messages over IP using SCTP. M3UA-connected IP endpoints do not have to conform to standard SS7 topology, because each M3UA association does not require an SS7 link; there are no 16-link-per-linkset restrictions. Each M3UA-connected IP endpoint can be addressed by an SS7 point code unique from the signaling gateway’s point code. Oracle offers two types of topologies for M3UA: IPGWx using routing keys, and IPSG using IPSG-M3UA links.

Note:

A-links for nodes requiring in-sequence delivery of messages should be configured on the IPLIMx card using M2PA; M3UA does not have sequence numbers to support lossless changeover/changeback.

A routing key defines a set of IP connections as a network path for a portion of SS7 traffic, and is the IETF Signaling Gateway equivalent of a Signal Transfer Point’s SS7 route. Routing keys are supported by the M3UA protocols to partition SS7 traffic using combinations of Destination Point Code (DPC), Origination Point Code (OPC), Service Indicator (SI), Network Indicator (NI), SS7 Subsystem Number (SSN), and/or Circuit Identification Code (CIC) message fields.

Using IPGWx, M3UA-connected IP endpoints do not have to conform to standard SS7 topology, because each M3UA association does not require an SS7 link; there are no 16-link-per-linkset restrictions. Each M3UA-connected IP endpoint can be addressed by an SS7 point code unique from the signaling gateway’s point code.

M3UA can also be implemented using IPSG, supporting routing keys in the form of SS7 Routes referencing IPSG M3UA linksets rather than as distinct ‘routing key’ managed elements. Instead, it performs similarly to the M2PA protocol. Each M3UA association is viewed as a link by the core EAGLE, and each IPSG card can have up to 32 associations/links per card. MTP Origin-Based Routing cannot be used with adjacent point codes.

M3UA does not have a 272-octet Signaling Information Field (SIF) length limit as specified by some SS7 MTP3 variants. Larger information blocks can be accommodated directly by M3UA/SCTP without the need for an upper layer segmentation or re-assembly procedure, as specified by the SCCP and ISUP standards. However, a Signaling Gateway will enforce the maximum 272-octet limit when connected to a SS7 network that does not support the transfer of larger information blocks to the destination.

At the Signaling Gateway, M3UA indicates to remote MTP3 users at IP end points when an SS7 signaling point is reachable or unreachable, or when SS7 network congestion or restrictions occur.

Note:

IPGW and IPSG M3UA links cannot be in the same link set at the same time. However, the EAGLE allows IPGW and IPSG-M3UA link sets to have separate routes to the same AS, aiding in cutover.