522 Chapter 06. SCCP: Signalling Connection Control Part of SS7 Protocol Description-- Signaling Connection Control Part (SCCP), a routing protocol in the SS7 protocol suite (in layer 4), provides end-to-end routing for TCAP messages to their proper databa- ses. SCCP provides connectionless and connection-oriented network services above MTP Level 3. While MTP Level 3 provides point codes to allow messages to be addressed to specific signaling points, SCCP provides subsystem numbers to allow messages to be addressed to specific appli- cations or subsystems at these signaling points. SCCP is used as the transport layer for TCAP- based services such as free phone (800/888), calling card, local number portability, wireless roam- ing, and personal communications services (PCS). SCCP also provides the means by which an STP can perform global title translation (GTT), a procedure by which the destination signaling point and subsystem number (SSN) is determined from digits (i.e., the global title) present in the signaling message. The global title digits may be any sequence of digits, such as 800/888 number, pertinent to the service requested.