tailieunhanh - Signaling System No.7 Protocol Architecture And Sevices part 32

Routes messages received from the MTP to appropriate local subsystem. Routes messages from local subsystems to other local subsystems. Routes messages from local subsystems to subsystems in remote | SCCP Routing Control SCRC SCRC performs the following three functions Routes messages received from the MTP to appropriate local subsystem. Routes messages from local subsystems to other local subsystems. Routes messages from local subsystems to subsystems in remote nodes by utilizing MTP s transport services. The destination is specified in the called party CdPA address parameter which is supplied by the subsystem. The address can contain a combination of point code system number and global title. SCCP addressing capabilities are flexible in contrast to those of MTP 3. As a result the addressing capabilities are somewhat complex thereby allowing several different combinations of routing parameters. SCCP provides a routing function that allows signaling messages to be routed to a signaling point based on dialed digits for example. This capability is known as Global Title Translation GTT which translates what is known as a global title for example dialed digits for a toll free number into a signaling point code and a subsystem number so that it can be processed at the correct application. The section on Global Title Translation explains global titles and GTT. The following are different types of network addressing that SCCP supports Point Code PC routing Subsystem Number SSN routing Global Title GT routing The MTP layer can only use point code routing which is described in Chapter 7. Figure 9-9 shows a summary of MTP point code routing. Using MTP point code routing MSUs pass through the STPs until they reach the SP that has the correct DPC. The following sections describe the SSN and GT routing. Figure 9-9. Showing MTP Point Code Routing View full size image Subsystem Number SSN Routing As previously mentioned a subsystem is the name given to an application that uses SCCP applications are predominantly database driven except where ISUP is the subsystem for a limited number of supplementary services or where BSSAP uses SCCP for radio-related signaling in GSM . As .