TAILIEUCHUNG - Signaling System No.7 Protocol Architecture And Sevices part 27

SCCP Messages and Parameters A full list and descriptions of ITU-T and ANSI SCCP messages is provided in Appendix C. This section concentrates on the core messages and parameters | SCCP Messages and Parameters A full list and descriptions of ITU-T and ANSI SCCP messages is provided in Appendix C. This section concentrates on the core messages and parameters. Table 9-3 shows the full list of SCCP messages in a chart that shows the protocol class es in which the messages operate. Both ANSI 2 and ITU-T 60 have identical SCCP message sets. Table 9-3. The SCCP Message Types and Corresponding Protocol Class es SCCP Message Protocol Classes 0 1 2 3 CR Connection Request X X CC Connection Confirm X X CREF Connection Refused X X RLSD Released X X RLC Release Complete X X DT1 Data Form 1 X DT2 Data Form 2 X AK Data Acknowledgment X UDT Unitdata X X UDTS Unitdata Service xm XÜ1 ED Expedited Data X EA Expedited Data Acknowledgment X RSR Reset Request X RSC Reset Confirm X ERR Protocol Data Unit Error X X IT Inactivity Test X X XUDT Extended Unitdata X X XUDTS Extended Unitdata Service X XÜI LUDT Long Unitdata X X LUDTS Long Unitdata Service Xm Xlil 1 Type of protocol class is indeterminate absence of protocol class parameter . Message Structure Figure 9-7 shows the format of an SCCP message. Figure 9-7. The SCCP Message Structure View full size image Apart from the absence of a Circuit Identification Code field CIC field following the routing label the basic message format is the same as an ISUP message see Chapter 8 ISDN User Part ISUP . As with all other MTP users SCCP messages are composed of three parts a mandatory fixed part mandatory variable part and an optional part. All SCCP messages contain a mandatory fixed part but not all of them have parameters to place in the mandatory variable or optional part. The following sections describe these three parts in more detail. Mandatory Fixed Part MF The mandatory fixed part consists of those parameters that must be present in the message and that are of a fixed length. Because the parameters are of a fixed length and are mandatory no length indicator is required. In addition because the parameter types .

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