Signaling System No.7 Protocol Architecture And Sevices part 51

User Adaptation (UA) Layers The User Adaptation (UA) layers encapsulate different SCN signaling protocols for transport over an IP network using SCTP. While each UA layer is unique in terms of the encapsulation
Nội dung trích xuất từ tài liệu:
Signaling System No.7 Protocol Architecture And Sevices part 51User Adaptation (UA) LayersThe User Adaptation (UA) layers encapsulate different SCN signaling protocolsfor transport over an IP network using SCTP. While each UA layer is unique interms of the encapsulation because of the differences of the signaling protocolsthemselves, following are some common features among all UA layers: • Support for seamless operation of the UA layer peers over an IP network. • Support for the primitive interface boundary of the SCN lower layer, which the UA layer replaces. For example, M2UA supports the primitive interface boundary that MTP Level 2 supports. • Support for the management of SCTP associations. • Support for asynchronous reporting of status changes to layer management.The SigTran Working Group has defined several UA layers, which include thefollowing: • The MTP Level 2 User Adaptation (M2UA) layer is defined for the transport of MTP Level 3 messages between a SG and a MGC or IP database. • The MTP Level 3 User Adaptation (M3UA) layer is defined for the transport of SS7 User Part messages (such as ISUP, SCCP, and TUP) between an SS7 SG and a MGC or other IP Signaling Point (IPSP). • The SCCP User Adaptation (SUA) layer is defined for the transport of SCCP User Part messages (such as TCAP and RANAP) from an SS7 SG to an IP-based signaling node or database, or between two endpoints in the same IP network. • The MTP Level 2 Peer Adaptation (M2PA) layer is defined for the transport of MTP Level 3 data messages over SCTP. M2PA effectively replaces MTP Level 2. It provides the ability to create an IP-based SS7 link. • The ISDN User Adaptation (IUA) layer is defined for the transport of Q.931 between an ISDN SG and a MGC. IUA supports both Primary Rate Access and Basic Rate Access lines.Each of these adaptation layers will be discussed in detail, with the exception ofIUA because it is beyond the scope of this book. Other proposed adaptation layers(such as DPNSS/DASS2 DUA [144] UA and V5.2 V52UA [145] UA) are beingworked on in the SigTran Working Group; however, like IUA, those adaptationlayers are beyond the scope of an SS7 discussion.When these adaptation layers were being developed, it became evident that someterminology and functionality were common, with the exception of M2PA. Therewas an effort to keep the UA documents synchronized with common text for theseterms and functional discussions.UA Common TerminologyThe UAs introduce some new terminology that did not exist in the SS7 world.Some of these terms are common across all of the SS7 UAs; therefore, it is worthdiscussing them before starting with the adaptation layers. Following are thedefinitions of these terms, provided by RFC 3332 [137]: • Application Server (AS)— A logical entity that serves a specific Routing Key. An example of an Application Server is a virtual switch element that handles all call processing for a unique range of PSTN trunks, identified by an SS7 SIO/DPC/OPC/CIC_range. Another example is a virtual database element, handling all HLR transactions for a particular SS7 DPC/OPC/SCCP_SSN combination. The AS contains a set of one or more unique ASPs, of which one or more is normally actively processing traffic. Note that there is a 1:1 relationship between an AS and a Routing Key. • Application Server Process (ASP)— A process instance of an Application Server. An ASP serves as an active or backup process of an Application Server (for example, part of a distributed virtual switch or database). Examples of ASPs are processes (or process instances) of MGCs, IP SCPs, or IP HLRs. An ASP contains an SCTP endpoint and can be configured to process signaling traffic within more than one Application Server. • Signaling Gateway Process (SGP)— A process instance of a SG. It serves as an active, backup, load-sharing, or broadcast process of a SG. • Signaling Gateway (SG)— An SG is a signaling agent that receives/sends SCN native signaling at the edge of the IP network. An SG appears to the SS7 network as an SS7 Signaling Point. An SG contains a set of one or more unique SG Processes, of which one or more is normally actively processing traffic. Where an SG contains more than one SGP, the SG is a logical entity, and the contained SGPs are assumed to be coordinated into a single management view to the SS7 network and the supported Application Servers. • IP Server Process (IPSP)— A process instance of an IP-based application. An IPSP is essentially the same as an ASP, except that it uses M3UA in a point-to-point fashion. Conceptually, an IPSP does not use the services of a SG node. ...