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Signaling System No.7 Protocol Architecture And Sevices part 33

SCCP Management (SCMG) SCMG manages the status of subsystems and SCCP-capable signaling points (SPs). It maintains the status of remote SCCP SPs and that of local subsystems. It interacts with the SCRC | SCCP Management SCMG SCMG manages the status of subsystems and SCCP-capable signaling points SPs . It maintains the status of remote SCCP SPs and that of local subsystems. It interacts with the SCRC to ensure that SCCP traffic is not sent to inaccessible destinations if they are available they use alternative routes or alternative subsystems to provide SCCP traffic rerouting. In addition SCMG throttles SCCP traffic in the event of network congestion. SCMG uses the concept of a concerned subsystem or SP. A concerned subsystem or SP is marked as requiring immediate notification if the affected subsystem or SP status changes. An affected SP might not have any subsystems or SPs marked as concerned in this case when a subsystem fails or inaccessibility occurs at the affected SP it does not broadcast the status change. If it has entities marked as concerned it will broadcast the SSP message so the SCMG at the concerned entities can react to circumvent routing to the unavailable SP or subsystem. A response method is used when a message is received that is addressed to an unavailable subsystem from an SP subsystem that has not been notified of the status change. Upon receiving such a message the affected SP returns the SSP message. The notified SP subsystem can then periodically check whether the affected subsystem is available by sending a SCMG Subsystem status Test SST to the affected SP. The affected SP returns an SCMG Subsystem Allowed SSA message if the subsystem is available again. An SP subsystem might not have been notified of the status change because it was not on the concerned list the SSA SSP message sent from the affected SP was lost or the affected SP was recovering from either an MTP or SCCP failure in which case it does not make a broadcast upon recovery. Figure 9-22 presents an example of the response method. Figure 9-22. Possible Sequence of Messages Exchanged Between PC-Z and PC-Y When the Toll-Free Subsystem at PC-Z Becomes Unavailable In Figure 9-22 .