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Signaling System No.7 Protocol Architecture And Sevices part 52

MTP Level 3 UA (M3UA) M3UA [137] provides for the transport of MTP Level 3-user part signaling (such as ISUP and SCCP) over IP using SCTP. RFC 3332 defines and supplements it with an Implementers Guide [138]. M3UA provides for seamless operation between the user part peers by fully supporting the MTP Level 3 upper-layer primitives. M3UA can be used between an SG and an MGC or IP-resident database, or between two IPSP. The most common use for M3UA is between a SG and a MGC or IP-resident databases (such as SCPs). The SG receives SS7 signaling over standard SS7. | MTP Level 3 UA M3UA M3UA 137 provides for the transport of MTP Level 3-user part signaling such as ISUP and SCCP over IP using SCTP. RFC 3332 defines and supplements it with an Implementers Guide 138 . M3UA provides for seamless operation between the user part peers by fully supporting the MTP Level 3 upper-layer primitives. M3UA can be used between an SG and an MGC or IP-resident database or between two IPSP. The most common use for M3UA is between a SG and a MGC or IP-resident databases such as SCPs . The SG receives SS7 signaling over standard SS7 links. It terminates MTP Levels 1 to 3 and provides message distribution or routing of the user part messages that is destined for MGCs or IP-resident databases. The MGCs can send to other MGCs via the SG. Figure 14-11 shows the protocol stacks at each network element for using M3UA between a SG and a MGC. The SEP or SEP is a node in the SS7 network. The NIF or Nodal Interworking Function provides for the interworking of SS7 and IP. RFC 3332 does not define the functionality of the NIF because it was considered out of scope. Figure 14-11. Use of M3UA Between a SG and a MGC The M3UA on the MGC or IP-resident database supports the MTP Level upperlayer primitives so the user parts are unaware that MTP is terminated on the SG. The MTP service primitives 49 consist of the following MTP Transfer request and indication MTP Pause indication MTP Resume indication MTP Status indication The MTP Transfer primitive is used to pass user data. MTP Pause indicates that an Affected Point Code is Unavailable and MTP Resume indicates that an Affected Point Code is Available. MTP Status provides congestion and User Part Availability information on an Affected Point Code. Later in the Messages and Formats description of M3UA messages it will be clear how these primitives are supported. The M3UA layer on the SGP must maintain the state of all the configured ASPs and ASes. M3UA at the ASP must maintain the state of all configured SGPs and .