SCCP supported services in addition to MTP3 of OSI “Network layer” by supporting capability to transfer NSDU’s.
MTP-3 supports messages delivered end-destination based on DPC, and using SIO (4-bits) to distribute messages with-in the local node.
To this SCCP suppliments the capability of supporting Global Titles and SSN, where GTT can be used to identify a SS7-node globally and SSN to identify the specific application locally.
supporting GTT by SCCP means, decoding GTT into DPC and SSN.
Also, SCCP supports for class of communication Class 0 to 3, where 0 and 1 are connection-less ( like UDP) where in later one supports message sequencing capability.
Class 2 and 3 support connection-oriented where in later one supports “Flow-Control”.
TCAP exploits the capabilities of SCCP to support non-circuit signaling between two end-points ( SS7 TCAP based applications) by supporting remote-procedure execution on other node and providing facilities to transfer the results.
For more on SCCP read ITU-T Recommendations Q.711 up to Q.716 and for TCAP refer to Q.771 to Q.774
Hope this helps……..