SS7 is a protocol used by the telecommunications industry for out of band signaling. It provides fault-tolerant access to many services that are used every time a phone call is placed. These services include: ISUP, CLASS, CNAM, E800, LNP, AIN, IS41, and LIDB. A typical american network is arranged with a particular switch or SSP linked to one or more pairs of STPs which are also linked to each other. These STPs are then linked to other SSPs, STPs, and SCPs.

I forgot to mention that the services are divided into two catagories; ISUP and TCAP. ISUP is call completion, and TCAP is everything else.