Infrastructure for Transactions

Figure 13.2-2 shows the SS7 entities at a signaling point that are involved in the transfer of transaction messages.

Signaling Point C Signaling Point A Signaling Point B

(OAM Center) (Echange) (Network Database)

Signaling Point C Signaling Point A Signaling Point B

(OAM Center) (Echange) (Network Database)

Components

Components

Figure 13.2-1 Application service elements.

Components

Components

Figure 13.2-1 Application service elements.

The ASEs in a signaling point are the users of the transaction capabilities application part (TCAP) of signaling system No.7. In turn, TCAP is a user of the signaling connection control part (SCCP), and SCCP uses the services of the message transfer part (MTP) (Chapter 8).

In the CCITT/ITU-T model of SS7, an ASE passes its outgoing components to TCAP, in TC-request primitives. TCAP places one or more components in a TCAP message (or TCAP package), which is passed to SCCP in a N-unitdata request. SCCP then builds a SCCP message, and passes it to MTP in a MTP-transfer request. Finally, MTP forms a message signal unit (MSU), which is sent out on a signaling link (Section 8.8).

Incoming components arrive in MSUs on a signaling link. MTP extracts the SCCP message, and passes it to SCCP in a MTP-transfer indication. In turn,

Signaling Point A

Signaling Point A

Link

SCCP extracts the TCAP package, and passes it to TCAP in a N-unitdata indication. Finally, TCAP extracts the component(s) and passes them to the appropriate ASE, in TC-indications.

SCCP and TCAP are described in Chapters 14 and 15.

0 0

Post a comment